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					Abstract of thesis entitled ‘Longitudinal
study of contact lens care in Hong Kong and
the effect of interventions on compliance’
submitted by Yung Mo Sze for the degree of
Master of Philosophy at The Hong Kong
Polytechnic University in April 2004




                                 Abstract

Background

Increasing usage of contact lenses for vision correction has been reported in

Hong Kong and South China. It has been estimated that there are currently over

six hundred thousand contact lens wearers in Hong Kong. In order to get a

clearer picture of the use of contact lenses, there is a need to determine current

trends in contact lens usage, the level of microbiological contamination of

contact lenses, the level of compliance of contact lens wearers, and lens care

accessories.



Purpose

The objectives of this study were (1) to report practitioners’ preferences and

prescribing habits of contact lenses, their management of contact lens patients,

and to evaluate the use of speciality contact lenses and the development of the

contact lens market in Hong Kong; (2) to study the level of microbial

contamination and identify contaminants associated with contact lenses, lens

cases, and opened lens care solutions used by contact lens wearers; (3) to

determine the level of compliance of contact lens wearers, and to identify

common non-compliant procedures during contact lens handling; (4) to study the




                                                                                 i
effect of a compliance enhancement strategy (regular self-review exercise) on the

level of compliance.



Method

The usage of contact lenses was studied by means of a large scale survey. A total

of 1306 questionnaires were sent to all registered contact lens practitioners in

Hong Kong, asking for information about their choices of types of contact lenses

prescribed and lens care products recommended; their usage of speciality contact

lenses, and their opinions on future trends of contact lens development in Hong

Kong.

The levels of microbial contamination of contact lenses and lens care accessories

were studied by bacterial culture of the collected contact lenses, lens cases, and

lens care solutions of a group of young and asymptomatic contact lens wearers.

The contaminants associated with these items were identified using standard

microbiological techniques. Contamination rates of these samples were recorded

and compared with those reported in previous studies.

To study the level of compliance, a group of contact lens wearers were

interviewed to collect information on how they used and handled their contact

lenses. The level of compliance for each subject was evaluated with a self-

administered questionnaire together with microbiological examination of their

contact lenses, lens case and lens care solutions.

The effect of the intervention on the level of compliance was studied by

separating subjects into test and control groups, with a regular self-review

exercise on proper lens handling being given to the test group once every 3

months for 12 months. The level of compliance between test and control groups



                                                                                ii
was compared at the end of the 12 month period to evaluate the effect of the

intervention.



Result

Vision correction with contact lenses in Hong Kong

Our survey results showed that, soft, planned replacement, contact lenses

together with multipurpose solutions dominated the contact lens market in Hong

Kong. Usage of rigid lenses had not increased over the past few years, and the

usage of speciality contact lenses, especially overnight orthokeratology and

silicone hydrogel lenses was limited. Dryness was the major problem reported by

contact lens wearers. Practitioners look forward to further development of

custom-made toric, multifocal and silicone hydrogel lenses; and continuous

education courses that could fit their needs.



Contamination of contact lenses

Contact lenses, lens cases, and lens care solutions of the 101 asymptomatic

contact lens wearers were tested for microbial contamination. At least one of the

collected samples of around half of our subjects were found to be contaminated.

Of the samples tested, 9% of lens extracts, 34% of case extracts and 11% of

solutions were contaminated with potential pathogenic bacteria. Serratia,

Staphylococcus aureus, coagulase-negative staphylococci, Acinetobacter, and

Pseudomonas were the most common micro-organisms isolated from the

cultured samples. Lens cases were the most frequently contaminated item, and

they also supported the growth of the widest variety of bacterial species. Contact

lenses and lens cases used on an occasional-wear basis, and lens care solution



                                                                               iii
used by contact lens wearers with longer contact lens experience were associated

with higher contamination rates. Rinsing contact lenses with either saline or

multipurpose solution after cleaning was found to be an effective way to prevent

contact lens contamination.



Level of compliance of contact lens wearers and the effect of interventions

Information of 65 contact lens wearers on how they handled their contact lenses

and lens care accessories was collected by questionnaire. Our study illustrated

that all of the contact lens wearers showed some degree of non-compliance in the

care of their contact lenses and lens accessories. Of 15 lens care procedures, most

subjects were non-compliant with up to seven procedures. Common non-

compliant behaviours among contact lens wearers included: not disinfecting the

lens case weekly, not re-disinfecting contact lenses after they have been left in

lens case for longer than indicated, not cleaning the lens case with contact lens

solution, not changing lens cases every 3 months, not checking the expiry dates

of contact lens solutions, and not discarding solution and air drying the lens case.

Our compliance enhancement strategy (regular self-review exercise) did not

significantly improve the level of compliance, mainly because compliance

improved in both test and control groups. The contamination of contact lenses

and lens care accessories was lowered with the improvement in the level of

compliance.



Conclusion

There is increased demand for convenient contact lens wear. The use of over-

night wear contact lenses such as those used for orthokeratology and silicone



                                                                                  iv
hydrogel lenses were limited due to the practitioners’ concerns about safety. Our

findings demonstrate that contact lenses, lens case and lens care accessories are

not well maintained by contact lens wearers. Nearly half of the contact lens

wearers are using either contaminated contact lenses or lens care accessories.

This is probably due to the low level of compliance among contact lens wearers.

All of our subjects showed some degree of non-compliance and the spectrum of

non-compliance is wide. Our compliance enhancement strategy (regular self-

review exercise) did not show a significant effect on the level of compliance.

Further investigations are required to study new methods to prevent

contamination of contact lenses and lens care accessories, and to improve the

level of compliance among contact lens wearers.




                                                                               v
               Publication from the thesis


Yung MS, Cho P, Yap M. (2005) A market survey of contact lens practice in

Hong Kong. Clin Exp Optom 88:165-175.



Yung MS, Boost M, Cho P and Yap M. (2005) Microbial contamination of

contact lenses and lens care accessories used by soft contact lens wearers

(university student) in Hong Kong. Submitted to OPO




                                                                        vi
                       Acknowledgements


I am grateful to have Dr. Pauline Cho to be my chief supervisor. It is

impossible to acknowledge adequately for her guidance and support in my

study. Dr. Cho has taught me a lot on how to perform a research study and

write thesis. She has also provided many invaluable advice and guidance

during all stages of the research study.



I would like to thank Dr. Maureen Boost, my co-supervisor. Dr. Boost has

been very kind and patient in teaching me how to conduct microbiological

examination and she has provided a lot of advice on my thesis and

manuscripts.



I would like to thank Prof. Maurice Yap, my co-supervisor. Prof. Yap has

kindly given me much advice during my research study, and for these, I am

grateful.



Special thanks to Mr. William Kwan and my family for their great support.

I would also like to thanks all my research colleagues for sharing their

research experiences, and their support is much appreciated.



This research was supported by the Teaching Company Scheme:

collaboration between the Hong Kong Polytechnic University and Johnson

& Johnson Vision Care (HK) Ltd.




                                                                      vii
                             Table of Contents
Abstract                                                              i
Publication from the thesis                                           vi
Acknowledgements                                                      vii
Table of contents                                                     viii
List of tables                                                        xiii
List of figures                                                       xvi
List of abbreviations                                                 xvii


Chapter 1         The usage of contact lenses                         1
1.1    The usage of contact lenses                                    3
       1.1.1 Rigid lenses                                             3
                  1.1.1.1 PMMA                                        4
                  1.1.1.2 RGP                                         4
                  1.1.1.3 Orthokeratology                             5
       1.1.2      Soft contact lenses                                 6
                  1.1.2.1 Silicone hydrogel lenses                    8
       1.1.3      Summary                                             9


Chapter 2         Contact lens-associated microbial keratitis         11
2.1    Annual incidence                                               12
       2.1.1 Visual outcome                                           13
       2.1.2      Summary                                             14
2.2    Microbial keratitis inducing pathogens                         14
       2.2.1      Bacteria                                            16
                  2.2.1.1 Pseudomonas aeruginosa                      16
                  2.2.1.2 Serratia marcescens                         17
                  2.2.1.3 Staphylococcus                              18
       2.2.2      Fungi                                               20
       2.2.3 Protozoa                                                 21
       2.2.4      Summary                                             22
2.3    Risk factors for contact lens-associated microbial keratitis   23
       2.3.1      Summary                                             25


                                                                            viii
2.4   Physiological changes associated with contact lens wear           26
      2.4.1   Alteration of ocular flora                                26
      2.4.2   Changes in tear components                                28
      2.4.3 Hypoxia and hypercapnia                                     29
      2.4.4   Reduced corneal pH                                        30
      2.4.5   Corneal epithelial changes                                31
      2.4.6   Corneal endothelial changes                               33
      2.4.7   Corneal sensitivity                                       33
      2.4.8   Summary                                                   34


Chapter 3     Contamination of contact lenses and lens care
              Accessories                                               35
3.1   Contamination of contact lenses                                   37
      3.1.1   Sources of contact lens contaminants                      40
      3.1.2 Factors contributing to the contamination of contact lenses 41
              3.1.2.1 Lens materials                                    41
              3.1.2.2 Lens wear and lens deposits                       43
              3.1.2.3 Biofilm formation                                 44
      3.1.3   Summary                                                   45
3.2   Contamination of lens cases                                       46
      3.2.1   Factors contributing to the contamination of lens cases   50
      3.2.2   Summary                                                   51
3.3   Contamination of lens care solutions                              52
      3.3.1   Summary                                                   54
3.4   Effectiveness of contact lens care solution against microbial     54
      contamination
      3.4.1   Hydrogen peroxide system versus chemical disinfecting     55
              system
      3.4.2 One-step versus two-step hydrogen peroxide system           57
      3.4.3   Summary                                                   58


Chapter 4     Contact lens care compliance                              60
4.1   Studies of lens care compliance                                   60
      4.1.1   Study design                                              61


                                                                             ix
4.2   Non-compliant behaviours identified                               64
4.3   Clinic significations of non-compliant behaviours                 68
4.4   Reasons of non-compliance in contact lens wear                    70
4.5   Enhancement education on compliance                               73
4.6   Summary                                                           74


Chapter 5       Vision correction with contact lenses in Hong Kong      76
5.1   Aims                                                              76
5.2   Methodology                                                       77
      5.2.1 Investigation techniques                                    77
      5.2.2     Subject selection criteria                              78
5.3   Results                                                           79
      5.3.1     Response rate                                           80
      5.3.2     Refractive errors of contact lens wearers               80
      5.3.3     Number of aftercare visits                              81
      5.3.4 Contact lens types                                          82
      5.3.5 Commonly recommended wearing schedule                       84
      5.3.6     Use of toric contact lenses                             84
      5.3.7     Management of presbyopic contact lens wearers           85
      5.3.8     Recommended contact lens care regimen and use of daily 86
                cleaner
      5.3.9     Recommended enzymatic cleaning schedule                 87
      5.3.10 Common complaints of contact lens wearers                  88
      5.3.11 Availability and future development of specialty contact   89
                lenses
      5.3.12 Sources of contact lens information                        89
      5.3.13 Promote the use of contact lenses                          89
5.4   Discussion                                                        90
5.5   Conclusion                                                        94


Chapter 6       Microbial contamination of soft contact lenses, lens
                cases and lens care solutions                           95
6.1   Aims                                                              95
6.2   Ethics Approval                                                   96


                                                                             x
6.3   Methodology                                                          96
      6.3.1     Subject recruitment                                        96
      6.3.2 Sample collection                                              97
      6.3.3     Microbiological techniques                                 98
      6.3.4     Statistical analyses                                       99
6.4   Results                                                              99
      6.4.1     Subject demographics                                       99
      6.4.2     Incidence of microbial contamination                       101
      6.4.3     The effect of contact lens usage and lens care habits on   103
                microbial contamination
      6.4.4     Isolated contaminants                                      108
6.5   Discussion                                                           109
6.6   Conclusion                                                           114


Chapter 7       Longitudinal study on the effect of a compliance
                enhancement strategy (self-review exercise) on the
                level of lens care compliance and contamination of
                contact lenses and lens care accessories                   116
7.1   Aims                                                                 116
7.2   Ethics approval                                                      117
7.3   Methodology                                                          117
      7.3.1     Subject recruitment                                        117
      7.3.2     Compliance assessment by questionnaire                     117
      7.3.3     Compliance enhancement strategy                            118
      7.3.4     Microbial examination of contact lens and lens care        120
                accessories
      7.3.5     Statistical analyses                                       120
7.4   Results                                                              121
      7.4.1 Study population                                               121
      7.4.2     Overall non-compliance                                     121
                7.4.2.1 Non-compliant lens care procedures identified      122
      7.4.3     Compliance enhancement strategy                            124
                7.4.3.1 The level of compliance before and after treatment 127
                7.4.3.2 The effect of compliance enhancement strategy      131


                                                                                 xi
7.5   Discussion                                                        132
      7.5.1    Compliance assessment techniques                         133
      7.5.2    Level of compliance among contact lens wearers           133
      7.5.3    The effect of compliance enhancement strategy            136
7.6   Conclusion                                                        140


Chapter 8      Conclusions                                              141
      8.1      The usage of contact lenses                              141
      8.2      Contamination of contact lenses                          141
      8.3      The level of compliance and the effect of intervention   142
               on the level of compliance
      8.4      Further investigations                                   142


Appendix I                                                              144
Appendix II                                                             149
Appendix III                                                            154
Appendix IV                                                             157
References                                                              158




                                                                              xii
                              List of tables


Table 1.1     Classification and restriction on the practice of the         2
              Optometrist Register in Hong Kong
Table 1.2     The use of soft contact lenses, rigid gas permeable           3
              and polymethoylmeth acrylate lenses reported by
              previous studies
Table 2.1     Annual incidence of contact lens-associated microbial         12
              keratitis (Incidence per 10,000 wearers)
Table 2.1.1   Pathogens reported to be associated with microbial            15
              keratitis in contact lens wearers
Table 3.1     Percentage of contact lens-associated microbial keratitis,    35
              positive culture of corneal scrapes, and contact lenses or
              lens cases
Table 3.1.1   Contamination rates of contact lenses, lens case and          37
              solution reported by previous investigators
Table 3.1.2   Soft contact lens properties of different groups of           42
              lens polymers
Table 4.2.1   Summary of non-compliance behaviours found among              65
              contact lens wearers on hand cleaning, lens cleaning
              and lens disinfection
Table 4.2.2   Summary of non-compliance behaviours found among              66
              contact lens wearers on enzymatic cleaning, regular
              aftercare and lens replacement
Table 5.1     Classification and restriction on the practice of the
              Optometrist Register in Hong Kong Polytechnic
              University                                                    78
Table 5.3.1   Numbers of responses from practitioners in each              79
              category of registration
Table 5.3.2   Most commonly recommended wearing schedules                  83
              (average) for each type of contact lenses
Table 6.4.1   Subject demographics                                         100



                                                                                 xiii
Table 6.4.2   Number and percentage of subjects with contaminated        101
              samples
Table 6.4.3   Incidence of microbial contamination                       102
Table 6.4.4   Association between contact lens experience, wearing       104
              schedules and the age of items, of subjects with and
              without contaminated items
Table 6.4.5   Effect of disinfecting regimen used and lens care          105
              procedures of contact lens wearers on the contamination
              rates of tested lenses
Table 6.4.6   Effect of disinfecting regimen used and case care          106
              procedures of contact lens wearers on the contamination
              rates of the tested case
Table 6.4.7   Effect of the disinfecting regimen used and solution care 107
              procedures of contact lens wearers on the contamination
              rates of the tested solutions
Table 7.4.1   Incidence of microbial contamination of in contact lenses, 124
              lens case and lens care solutions at the first visit
              (all subject)
Table 7.4.2   Subject demographics of Group 1 and 2                      124
Table 7.4.3   Non-compliance scores for each lens care procedure         126
              between the two groups of subjects at baseline
Table 7.4.4   Incidence of microbial contaminants in contact lenses,     127
              lens cases and lens care solutions between Group 1 and 2
              at baseline
Table 7.4.5   Incidence of microbial contamination in contact lenses,    130
              lens case and lens care solutions for Group 1 and 2
              subjects
Table 7.4.6   Non-compliance scores for each lens care procedure         131
              between the two groups of subject at final visit
Table 7.4.7   Incidence of microbial contamination in contact lenses,    132
              lens cases and lens care solutions at the final visit




                                                                               xiv
Table 7.5.1   The percentage of non-compliant subjects and importance 135
              rating of safety of each lens care procedures
              (Gower et al., 1994)




                                                                            xv
                            List of figures


Figure 5.3.1   Nature of practices that respondents worked in               79
Figure 5.3.2   Distributions of contact lens and non-contact lens           80
               wearers consulting the respondents
Figure 5.3.3   Comparisons of the proportions of different types of         81
               contact lenses prescribed between current findings and
               those reported by Cheung et al. (2002)
Figure 5.3.4   Comparisons of the proportions of different planned          82
               replacement soft contact lenses prescribed in the current
               study and in the study of Cheung et al. (2002)
Figure 5.3.5   Proportions of different management protocols for            85
               presbyopic contact lens wearers
Figure 5.3.6   Proportions of recommended disinfecting regimens for         86
               contact lens wearers
Figure 5.3.7   Common complaints made by contact lens wearers               88
Figure 6.4.1   Bacteria isolated from contaminated samples                 108
Figure 7.3.1   Flow chart of study procedures                              119
Figure 7.4.1   Distribution of subjects according to the number of         121
               non-compliant lens care procedures
Figure 7.4.2   Percentages of non-compliant and compliant subjects         122
               for each lens care procedure
Figure 7.4.3   Graphs (a) to (o) represent the percentage of compliant     128
               subjects (included both Group 1 and 2) for each lens care
               procedure at the beginning and at the final visit




                                                                                 xvi
                 List of abbreviations



BA        Blood agar

CNS       Coagulase-negative Staphylococcus

CI        Confidence Interval

CLED      Cystine lactose electrolyte deficient agar

DW        Daily wear

EW        Extended wear

MPS       Multipurpose solutions

NEO       Neomycin blood agar

OR        Odds Ratio

Ortho-k   Orthokeratology

Dk        Oxygen transmissibility

PBS       Phosphate-buffered saline

PR        Planned Replacement

PMMA      Polymethylmethacrylate

PN/Fp     Pyridine nucleotides/Oxidized flavoproteins

RGP       Rigid gas permeable

SDA       Sabouraud dextrose agar

SH        Silicone hydrogel

t         Thickness of the contact lenses

TSA       Tryptic soy agar




                                                        xvii
                                                                          Chapter 1




Chapter 1

The usage of contact lenses


The history of contact lenses began in 1887 with August Muller, who made

himself the first pair of contact lenses using polished ground glass (Heitz, 1984;

Pearson and Efron, 1989). After more than a hundred years of development,

contact lenses have now become a very popular vision correction device. In 2000s,

it was estimated that there were approximately 75 - 80 million contact lens wearers

worldwide (McMahon and Zadnik, 2000; Barr, 2000). Hong Kong is a place with

high incidence of myopia (Lam et al., 1991; Goh et al., 1993), hence a high

demand of contact lenses is expected. However, only a few studies on the usage of

different types of contact lenses have been carried out in this region.



The first study on the local use of contact lenses was carried out at The Hong Kong

Polytechnic University in 1990’s (Conway and Cho, 1990). However, in the last

decade, several major developments have occurred in the field, including the

increasing popularity of planned replacement (PR) and orthokeratology (ortho-k),

and the introductions of new hyper-oxygen transmissibility contact lenses, silicone

hydrogel (SH) lenses.




                                                                             1
                                                                             Chapter 1


Table 1.1 Classification and restriction on the practice of the Optometrist Register
in Hong Kong

Part of      Qualification/eligibility                    Restriction on practice
Register
   I         Bachelor degree/Professional Diploma         May use diagnostic
             in Optometry                                 pharmaceutical agents
    II       Higher Certificate in Optometry or other     Not allowed to use
             qualifications together with training,       diagnostic
             professional experience and skill            pharmaceutical agents
             satisfying the Council*                      except staining agents
    III      The applicant has acquired substantial       To practise refraction
             knowledge, experience and skill in the       only
             practice of his profession
   IV        The applicant has acquired substantial       Not allowed to use
             knowledge, experience and skill in the       diagnostic agents except
             practice of his profession or passed         staining agents
             Optometrists Board examination on
             refraction and contact lens fitting
   IV        The applicant has acquired substantial       To practise refraction
             knowledge, experience and skill in the       only
             practice of his profession or passed
             Optometrists Board examination on
             refraction
*the Council: the Supplementary Medical Professionals Ordinance


In addition to change in types of lens, an important change in Hong Kong was the

introduction of controlling legislation on practitioners who can fit contact lenses in

1996 (Cheung et al., 2002). Before the legislation to control optometry was

introduced in 1996, anybody, with or without professional qualification, could

prescribe contact lenses. After the legislation, only appropriately registered

optometrists, with recognized levels of contact lens experience, were allowed to

carry out contact lens practice. Optometrists who are allowed to fit contact lenses

include: Part I, Part II, and some of Part IV optometrists (See Table 1.1). This

controlling legislation was introduced to promote the standard of the profession

and to ensure that the general population would receive proper care of their ocular

health.




                                                                                2
                                                                                  Chapter 1



1.1 The usage of contact lenses

In line with the development in technologies, the usage of contact lenses has

changed rapidly over the last decade. A summary of the recent reports on the usage

of contact lenses in Hong Kong and other countries are presented in Table 1.2.



Table 1.2 The use of soft contact lenses, rigid gas                       permeable       and
polymethylmethacrylate lenses reported by previous studies.


                                                  Soft Contact
                                                     Lenses       Rigid gas     Polymethylmeth-
                                                    (Planned      permeable         acrylate
                                                  replacement       lenses
                                                     lenses)
Conway and                           76
                      HK                             78%            14%               8%
Cho, 1990                        optometrists
                                      174
                                  individuals
Cho et al., 1994      HK          working in         87%             9%               4%
                                  optometric
                                 related fields
                                                      84%
Barr, 2000            US               -                            16%                   -
                                                     (75%)
                                 163 Contact          88%
Lee et al., 2000   Singapore                                         8%                   -
                                 lens wearers        (44%)
                                                      90%
Tanner, 2000          UK               -                            10%                   -
                                                     (87%)
Woods and                            178           80-94%                          Around 3%
                   Australia                                       6-20%
Morgan, 2002                     optometrists     (71-91%)*                     (Queensland only)
Cheung et al.,                       275              88%           10%
                      HK                                                              1%
2002                             optometrists        (59%)       1% (ortho-k)
* Percentage among prescribed soft lenses.




1.1.1 Rigid lenses

In general, contact lenses could be subdivided into groups according to their

physical properties: rigid lenses and soft lenses. Rigid lenses can further be

subdivided into polymethylmethacrylate (PMMA) lenses and rigid gas permeable

(RGP) lenses.


                                                                                      3
                                                                              Chapter 1


1.1.1.1        PMMA

Rigid lenses prescribed in Hong Kong are mainly RGP lenses, PMMA lenses are

now seldom prescribed because PMMA, with low oxygen transmissibility (Dk),

can not satisfy corneal oxygen requirements as well as other types of lenses. This

is reflected elsewhere in the world. Usage of PMMA lenses reported in

Queensland was only around 3%, and no usage of PMMA was reported in other

areas of Australia (Woods and Morgan, 2002). PMMA lens use was found to have

ceased in recent contact lenses surveys carried in the United Kingdom, the United

State and Singapore (Barr, 2000; Lee et al., 2000; Tanner, 2000). In Hong Kong,

PMMA use had dropped 1% in 2000 (Conway and Cho, 1990; Cho et al., 1994;

Cheung et al. 2002).



1.1.1.2        RGP

RGP lens use in Singapore, the United Kingdom, Australia and the United States is

limited between 6% and 20% wearers (Barr, 2000; Lee et al., 2000; Woods and

Morgan, 2002). In general, practitioners predominantly fit soft lenses to new

contact lens wearers (Tanner, 2000; Woods and Morgan, 2002) and RGP lenses

are more likely to be prescribed for refit lens wearers. This is related to the initial

discomfort of RGP lens wear (Conway and Cho, 1990). There is also a report

suggesting that the use of RGP lenses has been further challenged by the

introduction of better soft lenses (Efron, 2000), such as the introduction of hyper

Dk SH lenses. SH has broken the limit of Dk available among soft contact lenses

allowing high oxygen permeability, which is thus no longer confined only to RGP

lenses (Efron, 2000; Cheung et al., 2002). However, RGP still has certain

advantages over soft lenses, including better tear exchange (Holden et al., 1988),



                                                                                 4
                                                                             Chapter 1


lower risk of contamination and reduced problems associated with solution

preservative (Key, 1990; Nilsson and Montan, 1994a; Chan and Weissman, 1996).



1.1.1.1        Orthokeratology

Ortho-k was developed based on studies on the reduction of myopia after the wear

of rigid lens performed since the late 1960’s. It was defined as the reduction,

modification, or elimination of refractive anomalies by the programmed

application of contact lenses (Tredici, 1979). In the early stage of ortho-k,

treatments were performed using spherical conventional rigid lenses. Later,

reverse geometry lenses, which can induce a faster corneal response, greater effect

on the reduction of refraction and better centration (Nichols et al., 2000; Sridhar et

al., 2001), were introduced and become the most preferred lens design.

The underlying mechanism of ortho-k is still uncertain. It has been suggested that

the hydraulic pressure of the tear layer, between the lens and cornea, produce

pressure against cornea (Coon, 1982). This pressure on the cornea leads to the

redistribution of corneal cells and provide temporary and reversible reduction in

myopia and astigmatism (Fan et al., 1999; Choi et al., 2001; Mountford and

Pesudovs, 2002). A mean reduction up to −3.00D could be achieved by ortho-k

(Fan et al., 1999). In a group of young myopic adolescents, maximum reduction of

myopia of up to −6.00D (Liu, 1999) was recorded. In general, ortho-k was found

to be effective in patient with astigmatism between −1.00D and −1.50D (Liu, 1999;

Mountford and Pesudovs, 2002). It has to be stressed that the effects of ortho-k in

the reduction of myopia are only temporary, and the changes can only be retained

with regular wear of lenses (Polse et al., 1983). Investigators have suggested that

ortho-k has some effect in controlling the progression of myopia (Polse et al., 1983;



                                                                                5
                                                                            Chapter 1


Grosvenor et al., 1989; Perrigin et al., 1990), however there is still a lack of

scientific evidence to support this.

In Hong Kong, the use of ortho-k only contributes to 1% of contact lens usage

(Table 1.2) (Cheung et al., 2002). Cho et al. (2003) studied demographic data of

ortho-k patients in private practices in Hong Kong and reported that 82% (50 out

of 61) of ortho-k wearers were children aged under 16 years, and overnight wear is

the main wearing modality.

The limited use of ortho-k in Hong Kong was due to safety concerns and the lack

of concrete scientific evidence regarding its control of myopia progression

(Cheung et al., 2002). Practitioners worried about the potentially serious

complications associated with overnight wear of these lenses (Cheung et al., 2002),

as there were reports of corneal ulcer associated with ortho-k wear (Chen et al.,

2001; Lau et al., 2003). Other factors limiting the usage of ortho-k include the lack

of appropriate training on fitting these lenses, high selling price, and uncertain

patient compliance (Cheung et al., 2002).



1.1.2 Soft contact lenses

Nowadays soft contact lenses are the most popular choice of contact lens wearers.

Over 80% of contact lens wearers use soft contact lenses in the United States,

Singapore, United Kingdom, Australia and Hong Kong (Barr, 2000; Lee et al.,

2000; Tanner, 2000; Woods and Morgan, 2002; Cheung et al., 2002). For many

years, a lot of resources have been injected into investigation of the development

of the ‘best’ soft lenses. Manufacturers have refined polymer formulations to

obtain the highest Dk (to reduce hypoxia effect) and the thinnest lenses (to provide

better comfort) with optimal water content (to maintain stability of lenses). These



                                                                               6
                                                                          Chapter 1


refinements allow soft lenses to be available in a variety of hydrogel polymers

with a wide range of water content and Dk. As mention previously, the latest

break-through for soft contact lenses was the introduction of SH lenses ⎯ contact

lenses with high Dk and low water content.



In Hong Kong, the usage of soft contact lenses has increased from 78% in 1990 to

88% in 2002 (Conway and Cho, 1990; Cheung et al., 2002). Since the introduction

of PR modalities in the later half of the 1990’s, the use of PR contact lenses has

grown rapidly and become the most popular lens-wearing modality.



As reported in 2002, the use of PR contact lenses has grown rapidly and they

account for 59% of the total contact lens use (Cheung et al., 2002). Similar trends

in usage of soft contact lenses has also been recorded in Singapore (Lee et al.,

2000)−among whose 88% of soft contact lens users, 44% choose PR contact

lenses. PR contact lenses are even more popular in the United States, the United

Kingdom and Australia. PR contact lenses now account for 75%-87% of total

contact lens usage in the United States and the United Kingdom respectively (Barr,

2000; Tanner, 2000), whereas in Australia, PR contact lenses now account for

71%-91% of the total soft contact lens usage (Woods and Morgan, 2002). In Hong

Kong, biweekly disposables followed by daily disposable are the most popular PR

contact lenses prescribed (Cheung et al., 2002), but daily and monthly disposables

are practitioners’ major choice in the United Kingdom (Tanner, 2000) and

Singapore (Lee et al., 2000) respectively.




                                                                             7
                                                                           Chapter 1


PR contact lenses were originally introduced to minimize infections associated

with contact lens wear by improving lens hygiene, as PR modality allows

simplified lens handling and lens replacement at higher frequency (McMahon and

Zadnik, 2000). However, epidemiologic studies have shown that PR contact lenses

used on both daily wear (DW) and extended wear (EW) basis cannot reduce the

incidence of contact lens-associated microbial keratitis (Nilsson and Montan,

1994a; Rattanatam et al., 2001). The wearing of PR contact lenses still leads to the

same metabolic and physiologic changes in the corneal epithelium as conventional

contact lenses in EW modality (Binder, 1981; Tsubota, 1992b). PR contact lenses

have become popular as their use allows convenient contact lens wear with

simplified lens care procedures, especially when used together with multipurpose

solutions (MPS). The use of PR contact lenses also lowered the prevalence of

some milder complications, reducing deposit-induced problems and eliminating

solution-related problems with the use of daily disposable lenses (Poggio and

Abelson, 1993; Solomon et al., 1996; Ilhan et al., 1998; Suchecki et al., 2000).



1.1.2.1        Silicone hydrogel lenses

EW refers to contact lens wear for a certain number of days (including nights)

before removing for cleaning and disinfection or for replacement with a new pair

of lenses. As EW requires overnight wear of contact lenses, lenses with high Dk

have to be used in order to provide adequate oxygen to satisfy corneal metabolic

requirements. Although there is a proportion of patients who want their vision

corrected at all the times, EW has never been the major lens wearing modality in

contact lens wear (Nichols et al., 2000). This is mainly because of practitioners’

concern associated with EW−induced complications (Barr, 2000). The risk of



                                                                              8
                                                                            Chapter 1


contact lens-associated microbial keratitis are well known to be increased with

EW, and it has been suggested that it results from combination of reduced oxygen

availability under closed lid conditions together with lens wear, lack of eye and lid

movement during sleeping (Goodlaw, 1996).

In the past, only high Dk RGP lenses with Dk approaching 100 are available in the

market. Recently this barrier has also been broken by newly introduced soft

contact lens material – SH. SH lenses having 5 to 10 times higher Dk (>100Dk)

compare with conventional EW hydrogel lenses (Compan et al., 2002) and with

water content remain at 24%-36%.

There are currently two SH contact lenses, the Balifilcon A and Lotrafilcon A,

available in Hong Kong, and they were only introduced after 2000 (Cheung et al.,

2002). In Hong Kong, SH contact lenses were usually prescribed for DW rather

than EW as promoted by manufacturers (Cheung et al., 2002). This was because

hyper Dk of SH contact lenses can only help to overcome hypoxia-induced

complications (Dumbleton et al., 2001), but not all problems related to EW wear

(Dumbleton et al., 2001; Dumbleton, 2003; Yeniad et al., 2004). This also explains

why there was an increased usage of SH contact lenses as problem-solving lenses

but not for EW (Cheung et al., 2002). Similar concerns were also observed in

Australia, where there was up to 24% of usage of EW in certain states however

most SH contact lenses were prescribed for DW rather than EW (Woods and

Morgan, 2002).



1.1.3   Summary

The usage of contact lenses changed with the development in manufacturing

technologies and introduction of better lens materials. There is also geographic



                                                                               9
                                                                          Chapter 1


difference on the usage of contact lenses. In Hong Kong, contact lens market is

dominated by soft lenses, particularly by PR lenses, where the usage of RGP and

ortho-k remained low. Nowadays, RGP lenses are usually fit after the failure of

soft contact lenses, where ortho-k lenses are mainly prescribed for myopia control.

There was no previous report on the usage of SH lenses since it has only

introduced to the market for a short period of time.




                                                                            10
                                                                              Chapter 2




Chapter 2

Contact lens-associated microbial
keratitis


In conjunction with the increasing usage of contact lenses, an increased occurrence

of corneal complications associated with contact lens wear is expected. Contact

lens-induced complications can range from mild to severe and common contact

lens-induced complications include allergic conjunctivitis (Binder et al., 1981),

giant papillary conjunctivitis (Suchecki et al., 2003), peripheral infiltrates

(Suchecki et al,. 2003), corneal staining (Lin and Mandell, 1991; Nichols et al.,

2002), neovascularization (Efron, 1987; Wong et al., 2003) and microbial keratitis

(Cohen et al., 1996; Bourcier et al., 2003; Mela et al., 2003; Suchecki et al., 2003).

Among these complications, contact lens-associated microbial keratitis is the most

serious and can lead to permanent visual loss. Contact lens wear has been

identified as an important predisposing factor of microbial keratitis and is

associated with 26% to 50% of microbial keratitis (Cohen et al., 1996; Houang et

al., 2001; Schaefer et al., 2001; Bourcier et al., 2003; Mela et al., 2003). The risk of

microbial keratitis further increases if contact lenses are used in the EW modality

(Chalupa et al., 1987; Nilsson and Montan, 1994a).




                                                                                 11
                                                                                 Chapter 2



2.1 Annual incidence
The findings of different investigators on the incidence of contact lens-associated

microbial keratitis are summarised in Table 2.1.



Table 2.1 Annual incidence of contact lens-associated microbial keratitis (Incidence
per 10,000 wearers).


Authors                Country       Daily wear soft      Extended wear        Daily wear
                                     contact lenses      soft contact lenses    rigid gas
                                                                               permeable
                                                                                  lenses
Poggio et al., 1989      USA               4.1                  20.9              4.0

Nilsson and Montan,
                       Sweden       2.2   (Disposable)   10.0 (Disposable)        1.5
1994a                               2.2 (Conventional)   13.3 (Conventional)

Cheng et al., 1999    Netherlands          3.5                  20.0              1.1

Seal et al., 1999      Scotland            2.7                    -               0.8



The incidence of contact lens-associated microbial keratitis differs for lens types

and lens wearing modalities (Poggio et al., 1989; Nilsson and Montan, 1994a;

Cheng et al., 1999). Among different lens types, DW RGP lenses are associated

with a lower incidence of microbial keratitis when compared to DW of soft contact

lenses (Table 2.1). For soft lenses, the incidence of microbial keratitis increased by

4.5 to 6 times, when lenses are used on an EW basis (Poggio et al., 1989; Nilsson

and Montan, 1994a; Cheng et al., 1999).

Nilsson and Montan (1994) compared the incidence of contact lens-associated

microbial keratitis between the use of conventional and PR soft contact lenses. For

DW, the annual incidence of microbial keratitis for conventional lenses is similar

to that reported for PR lenses. In contrast, recent studies show that PR lenses are

associated with more contact lens-associated microbial keratitis (Radford et al.,



                                                                                   12
                                                                            Chapter 2


1998a; Dejaco-Ruhswurm et al., 2001). In a study comparing 89 cases with 566

controls, the use of PR lenses was associated with 3.5 and 4.8 folds higher risk of

microbial keratitis than conventional lenses, when used in DW and EW,

respectively (Radford et al., 1998a). In a 12-month study in Austria, up to 89% of

cases of microbial keratitis were associated with the use of PR lenses

(Dejaco-Ruhswurm et al., 2001). The increased incidence of microbial keratitis

associated with the use of PR contact lenses, may be due to the significant increase

in the popularity of PR lenses in recent years (see Section 1.1.2). Stapleton, (2003)

suggested that the risk associated with the use of PR contact lenses could be over

estimated by investigators, as these studies usually do not exclude those patients

who used PR contact lenses to solve a problem. Therefore, it is still not possible to

conclude whether the occurrence of microbial keratitis is influenced by the use of

PR contact lenses.



2.1.1 Visual outcome

Around 40% of patients with microbial keratitis have been reported to have

reduced visual acuity and 5% of these patients suffer from very poor visual

outcome (Bourcier et al., 2003). Cohen et al., (1987) reported that the final acuity

of 12% of patients dropped to 6/60 or less, and this percentage further increased up

to 25% in Pseudomonas-infected eyes. In severe cases, keratoplasty may be

required to restore the vision of patients (Dejaco-Ruhswurm et al., 2001).




                                                                              13
                                                                            Chapter 2



2.1.2 Summary

DW rigid lenses are associated with the least number of cases of microbial keratitis.

Soft contact lenses used in EW modality show a higher incidence of microbial

keratitis than DW (Poggio et al., 1989; Nilsson and Montan, 1994a; Cheng et al.,

1999; Seal et al., 1999). Further investigations with better controls are required to

ascertain whether the use of PR contact lenses increases or decreases the risk of

microbial keratitis. Contact lens-associated microbial keratitis usually results in

reduction in visual acuity and some may end up with poor vision and require

keratoplasty.




2.2 Microbial keratitis inducing pathogens

Many microorganisms have been reported to be associated with contact

lens-associated microbial keratitis. Bacteria, fungi and protozoa are the common

pathogens involved in contact lens-associated microbial keratitis (Bennett et al.,

1998; Martins et al., 2002; Najjar et al., 2004). In some cases, positive corneal

cultures yield more than one microorganism (Mela et al., 2003). In the following

section, some common causes of contact lens-associated microbial keratitis

inducing bacteria, fungi and protozoa are introduced. A summary of contact

lens-associated microbial keratitis inducing pathogens is shown in Table 2.1.1.




                                                                              14
                                                                                Chapter 2


Table 2.1.1 Pathogens reported to be associated with microbial keratitis in contact
lens wearers.

 Microorganism                             Publication
 Gram-negative bacteria
 Acinetobacter spp.                        Bennett et al., 1998; Cheng et al., 1999
 Citrobacter freundii                      Mela et al., 2003
 Enterobacter spp                          Cheng et al., 1999
 Escherichia coli                          Cheng et al., 1999
 Hemophilus influenzae                     Mondino et al., 1986
 Klebsiella spp                            Cheng et al., 1999
 Morganella morgagni                       Mondino et al., 1986
 Proteus mirabilis                         Mondino et al., 1986
 Pseudomonas spp.                          Mondino et al., 1986; Chalupa et al., 1987;
                                           Cohen et al., 1987a; Cheng et al., 1999;
                                           Dejaco-Ruhswurm et al., 2001; Martins et
                                           al., 2002; Najjar et al., 2004
    P. aeruginosa                          Mondino et al., 1986; Chalupa et al., 1987;
                                           Bennett et al., 1998; Cheng et al., 1999;
                                           Tabbara et al., 2000; Mela et al., 2003
    P. mirabilis                           Mela et al., 2003
 Serratia spp.                             Cohen et al., 1987; Cheng et al., 1999;
                                           Najjar et al., 2004
    S. liquiformis                         Cheng et al., 1999
    S. marcescens                          Cheng et al., 1999; Mela et al., 2003
 Stenotrophomonas maltophilia              Cheng et al., 1999
 Gram-positive bacteria
 Bacillus spp                              Cheng et al., 1999
 Corynebacterium diphtheriae               Mondino et al., 1986; Cheng et al., 1999
 Diphtheroids                              Cohen et al., 1987
 Staphylococcus spp.                       Mondino et al., 1986; Chalupa et al., 1987;
                                           Cohen et al., 1987; Bennett et al., 1998;
                                           Cheng et al., 1999; Tabbara et al., 2000;
                                           Martins et al., 2002
    Coagulase-negative Staphylococcus      Bennett et al., 1998; Dejaco-Ruhswurm et
                                           al., 2001; Martins et al., 2002
 Nocardia spp.                             Bennett et al., 1998
 Propionibacterium acnes                   Mondino et al., 1986;
 Streptococcus spp.                        Bennett et al., 1998; Cheng et al., 1999;
                                           Dejaco-Ruhswurm et al., 2001

 Fungi
 Aspergillus flavus                        Wong et al., 1997
 Fusarium spp.                             Wong et al., 1997; Najjar et al., 2004

 Protozoa
 Acanthamoeba                              Cohen et al., 1996; Bennett et al., 1998;
                                           Dejaco-Ruhswurm et al., 2001; Martins et
                                           al., 2002




                                                                                    15
                                                                            Chapter 2



2.2.1 Bacteria

Bacteria are the most common pathogens involved in contact lens-associated

microbial keratitis. Clinical signs of bacterial keratitis include loss of epithelium

with or without punctate corneal staining, stromal infiltrates, corneal oedema,

conjunctival chemosis and mucopurulent discharge (Willcox and Holden, 2001).

A wide variety of bacteria is involved in contact lens-associated microbial

keratitis, and many are normal flora on the ocular surfaces. These normal floras

protect the eye from more virulent microorganisms but they also act as

opportunistic pathogens and induce microbial keratitis in those patients in whom

the cornea or immune system is compromised (Parkin et al., 1997; Wang et al.,

1998). Microbial keratitis can also be induced by bacteria colonized on

contaminated    contact    lenses   or   fingers   including    Coagulase-negative

Staphylococcus (CNS), Micrococcus spp., Chryseomonas spp. and Bacillus spp.

(Willcox et al., 1997).



2.2.1.1        Pseudomonas aeruginosa

P. aeruginosa is the predominant bacterium which is responsible for 23% to 60%

of contact lens-associated microbial keratitis (Cohen et al., 1996; Cheng et al.,

1999; Martins et al., 2002; Mela et al., 2003). P. aeruginosa is present in home

kitchens and is frequently isolated from areas associated with tap water, wet

objects or surfaces such as dish-washing sponges and sinks (Ojima et al., 2002). P.

aeruginosa is also found on the floor and wash basins in bath rooms (Ojima et al.,

2002). In addition, P. aeruginosa is commonly isolated from contaminated contact

lenses, lens cases and lens care solutions (Devonshire et al., 1993; Lipener et al.,

1995; Velasco and Bermudez, 1996).



                                                                              16
                                                                             Chapter 2


The extent of binding of P. aeruginosa to the cornea increases with contact lens

wear. Klotz et al. (1990) reported a significant increase (three to eight times higher)

in the number of P. aeruginosa adhering to rabbit cornea after one to five days of

EW of contact lenses. They suggested that this increase in P. aeruginosa binding

to the cornea is due to the biochemical changes on the corneal epithelium after the

EW of contact lenses. In another rabbit study, both the risk of developing and the

severity of P. aeruginosa keratitis were increased with the extent of exposure of P.

aeruginosa to the cornea (Lawin-Brussel et al., 1993). The results of these studies

provide some insights as to why EW wearers are predisposed to Pseudomonas

keratitis.

P. aeruginosa is a virulent pathogen with multiple virulence factors, including

elastase, alkaline protease, exotoxin A and exo-enzyme S (O’Callaghan et al.,

1996; Engel et al., 1997; Hobden, 2002; Krall et al., 2002). An extracellular slime

layer enables the Pseudomonas species to adhere to contact lens surfaces and

protects them from host defence mechanisms (Levine and Snyder, 1999). In

addition, P. aeruginosa has a greater ability to produce active protease IV, which

increases its virulence (Engel et al., 1997).



2.2.1.2        Serratia marcescens

S. marcescens, a member of the enterobacteria family, is another pathogen

commonly causing contact lens-associated microbial keratitis. It is associated with

other ocular complications such, as contact lens induced acute red eye (Holden,

1996) and even endophthalmitis (Cohen et al., 1987; al Hazzaa et al., 1992). It is

an opportunistic pathogen capable of various nosocomial infections (Cimolai et al.,

1997; Su et al., 2003; Torii et al., 2003) and is widely distributed in nature and



                                                                               17
                                                                           Chapter 2


hospitals. S. marcescens has been isolated from contact lenses, lens cases,

preserved lens care solutions, steroid suspensions and fingers of contact lens

wearers (Donzis et al., 1987; Mayo et al., 1987; Hume et al., 1996).

In a study on rabbit corneas, protease was found to be the major virulence factor of

S. marcescens. Serratia proteases damage the cornea by solubilization of the

corneal stromal proteoglycans, leading to the loss of ground substance (Lyerly et

al., 1981). Studies of Serratia keratitis induced by different strains of S.

marcescens, using a rabbit eye and Caenorhabditis elegans models, showed that

the pathologic changes induced by S. marcescens differ from species to species

and are related to the extra cellular signalling (Hume et al., 1999). Among Serratia

proteases, the 56 kDa metalloprotease may be the major protease contributing to

the cytotoxic activity of S. marcescens (Marty et al., 2002). S. marcescens has a

high resistance to a variety of antibiotics including norfloxacin, streptomycin,

ampicillin, erythromycin, tetracycline and chloramphenicol (Chen et al., 2003). It

is also resistant to phagocytosis by polymorphonuclear leukocytes in tears under

closed eye conditions, particularly when grown as a biofilm on contact lenses

(Hume et al., 2003).



2.2.1.3        Staphylococcus

Staphylococcus is an important member of the normal microbiota on skin, being

found frequently on fingers and the lid margins (HØvding, 1981; Larkin and

Leeming, 1991 Willcox et al., 1997). It is also a common contact lens-associated

microbial keratitis inducing pathogen. CNS, S. epidermidids, S. capisis and S.

warneri are common Staphylococci isolated from contact lenses, upper bulbar

conjunctiva, lower lid margins, tears and fingers of contact lens wearers



                                                                             18
                                                                            Chapter 2


(Callender et al., 1986; Elander et al., 1992; Fleiszig and Efron, 1992; Willcox et

al., 1997; Leitch et al., 1998). They gain access to surfaces through hand contact

and this explains the presence of Staphylococcus in domestic areas that are

frequently touched by hands, such as dish-washing sponges, the kitchen sink,

refrigerator door handle, faucet handles, cloth toys and other contact surfaces

(Ojima et al., 2002).

Alpha- and beta-toxin are the major virulence factors of S. aureus (O’Callaghan et

al., 1997; Hume et al., 2001). Direct application of purified alpha-toxin onto the

cornea resulted in corneal epithelial erosions and iritis, whereas the application of

beta-toxin resulted in scleral inflammation (O’Callaghan et al., 1997).

Filbronectin-binding proteins have been identified as virulence factors of S.

aureus; these proteins allow S. aureus to adhere and invade corneal epithelium

(Rhem et al., 2000; Jett and Gilmore, 2002).

S. aureus is well-known for its high resistance to antibiotics. The percentage of

fluoroquinolone-resistant S. aureus is increasing continuously (Goldstein et al.,

1999; Marangon et al., 2004). Up to 35% of S. aureus isolated from cornea or

conjunctiva were found to be resistant to ciprofloxacin, 35% were resistant to

ofloxacin and 33% were resistant to levofloxacin (Goldstein et al., 1999;

Marangon et al., 2004). Compared with ciprofloxacin, ofloxacin and levofloxacin,

the fourth generation fluoroquinolones are more effective against S. aureus.

Tested with fluoroquinolone-resistant S. aureus, 68% were susceptible to

moxifloxacin and eight per cent were susceptible to gatifloxacin (Kowalski et al.,

2003). The increasing antibiotic resistance developed among S.aureus has already

posed an alarming challenge to the treatment of contact lens-associated microbial

keratitis (Alexandrakis et al., 2000; Schaefer et al., 2001).



                                                                              19
                                                                         Chapter 2



2.2.2 Fungi

Compared with bacterial keratitis, fungal keratitis (keratomycosis) is relatively

rare. Keratomycosis is more commonly found in agricultural areas (Wong et al.,

1997). The ratio of fungal to bacterial keratitis is 1/17 in Hong Kong, 1/5 in

Singapore and 1/2 in South India (Houang et al., 2001). Clinical symptoms of

keratomycosis include redness, pain and the present of pus in the anterior chamber

(Armstrong, 2000; Willcox and Holden, 2001). At first, the patient may present

with a grey area of superficial necrosis with a dull dry surface, surrounded by

hyphate lines at the ulcer edge (Armstrong, 2000; Thomas 2003). It will progress

to stromal infiltrates and Desçemet’s folds (Rosa et al., 1994; Thomas, 1994).

Endothelial and anterior chamber involvement may occur after the first week

(Wilhelmus and Jones, 2001).

Keratomycosis can be induced by both filamentous and yeast-like fungi (Thomas

2003). Fusarium and Aspergillus are common pathogens causing filamentous

keratomycosis, whereas Candida is the most common cause of yeast-like

keratomycosis (Wong et al., 1997; Houang et al., 2001; Thomas, 2003). Fusarium

and Aspergillus are widespread throughout the environment. Fusarium is

frequently associated with vegetable matter and is responsible for most

keratomycoses in tropical areas (Levine and Snyder, 1999). Aspergillus is

widespread in the air, grains and soil and is commonly found in our respiratory

tract (Burge et al., 1980; Levine and Snyder, 1999). Candida is part of the normal

flora of skin, mouth, gastrointestinal and genitourinary tracts and sometimes on

the conjunctiva (Levine and Snyder, 1999). Fungi may gain access to the eyes

through random seeding and hence the incidence of keratomycosis is influenced

by environmental factors such as climate, rainfall and unbanization (Wong et al.,



                                                                           20
                                                                             Chapter 2


1997; Armstrong, 2000; Houang et al., 2001). Keratomycosis is more likely to

follow ocular trauma and foreign body injury than contact lens wear (Wong et al.,

1997; Thomas, 2003)



2.2.3 Protozoa

Acanthamoeba is the major protozoan causing keratitis among contact lens

wearers (Cohen et al., 1996; Najiar et al., 2004). Patients with acanthamoebic

keratitis usually suffer from severe or disproportionate pain (Moore et al., 1985).

In the early stage, patients may present with a superficial corneal lesion which

further progresses to perineural infiltrates, ring infiltrates and ulceration with

stromal lysis. In severe acanthamoebal keratitis, hypopyon, scleritis, secondary

glaucoma and cataract may also be present (Moore et al., 1985; Bacon et al., 1993;

Radford et al., 1998b).

In contrast to keratomycosis, amoebic keratitis is frequently associated with

contact lens wear. Radford et al., (2002) reported an annual incidence of amoebic

keratitis in England and Wales of 1.26 per million adults (age 15 years or above)

between 1997 and 1998 and 1.13 per million adults between 1998 and 1999

(Radford et al., 2002). For contact lens wearers, the annual incidence of amoebic

keratitis increased to 21.14 and 17.53 per million, respectively over the same

periods (Radford et al., 2002). The role of contact lenses in the development of

amoebic keratitis is still unclear. It has been suggested that the contact lenses, the

lens case and lens care solutions are contaminated by bacteria which may provide

a food source to facilitate the survival and growth of acanthamoeba (Bottone et al.,

1992). With co-contaminated contact lenses, both bacteria and acanthamoeba are

transferred onto the cornea. Following the exhaustion of bacteria, acanthamoeba



                                                                               21
                                                                             Chapter 2


will degrade corneal cells as a food substrate (Stopak et al., 1991), leading to

serious corneal damage.

The risk of acanthamoebic keratitis is geographically distributed in accordance

with the quality of the local water. Where limescale is present (Seal et al., 1992) or

where the water is hard, as in England and Wales the risk of acanthamoeba is three

times higher than in areas with a soft water supply (Radford et al., 2002).

Acanthamoeba is found in unclean water and can be cultured from bathroom and

kitchen tap water and from around washbasins (Moore et al., 1985; Seal et al.,

1992; Houang et al., 2001).

Although acanthamoebic keratitis is rare, it can lead to severe damage of the

cornea. Therefore, home made saline should not be used with contact lenses and

lens care accessories, which should not come in contact with tap water or any other

unclean water, such as water from puddles in rural areas (Seal et al., 1992, Radford

et al., 2002). Contact lenses should not be worn while swimming (Bottone et al.,

1992).



2.2.4          Summary
Contact lens-associated microbial keratitis can be induced by various

microorganisms which are widely distributed in nature. Bacteria are the main

culprits and many are opportunistic pathogens present on the human body as

normal flora. P. aeruginosa, S. marcescens and S. aureus are the most common

bacteria associated with keratitis (Cohen et al., 1996; Cheng et al., 1999; Martins

et al., 2002; Mela et al., 2003). Keratomycosis occurs but is less likely to be

associated with contact lens wear than ocular trauma (Wong et al., 1997; Thomas,

2003). Fusarium, Aspergillus and Candida are the most common fungi which




                                                                               22
                                                                              Chapter 2


cause keratitis (Wong et al., 1997; Houang et al., 2001; Thomas, 2003). Amoebic

keratitis is rare but it is highly associated with the use of contact lenses (Radford et

al., 2002). All these pathogens may gain access to eyes via unclean hands,

wearing contaminated contact lenses or by ocular trauma (Bloomfield and Scott,

1997).



2.3 Risk factors for contact lens-associated microbial
keratitis

As reported in Section 2.1, wearing contact lenses on an EW basis significantly

increases the risk of contact lens-associated microbial keratitis (Poggio et al., 1989;

Nilsson and Montan 1994a; Cheng et al., 1999). Overwear of contact lenses

disturbs the corneal metabolism, compromising corneal defence mechanisms

making the cornea more susceptible to infection (Holden and Sweeney., 1985a).

The risk of microbial keratitis is increased 3.51 times with unscheduled overnight

wear (Radford et al., 1998). Wearing therapeutic contact lenses on an EW basis is

another predisposing factor for microbial keratitis (Weissman and Mondino,

2002).



The intact corneal epithelium is the primary physical barrier, preventing adherence

of pathogens. Any disruption of this barrier will increase the risk of microbial

keratitis. Trauma to the corneal epithelium increases the risk of microbial keratitis

(Weissman and Mondino, 2002) and the risk is further increased if the trauma is

caused by a contaminated agent (Levin and Snyder, 1999). Corneal epithelial

defects can result from contact lens wear due to indentation from the lens edge,




                                                                                 23
                                                                            Chapter 2


allergy to lens care solutions, foreign bodies or air bubbles trapped under the

lenses and dehydration of the corneal epithelium (Bruce and Brennan, 1990).

Blepharitis is a presumed risk factor of microbial keratitis (Weissman and

Mondino, 2002). It interrupts the distribution of antimicrobial agents over the

cornea by compromising the tear film, as the abnormal blinking action of diseased

eyelids does not distribute tears evenly over the cornea (Weissman and Mondino,

2002).



An increased risk of microbial keratitis occurs in patients with chronic disease or

those who are immuno-suppressed. These patients are more susceptible to

infections and hence, patients with diabetes (Wipf and Paauw, 2000), human

immunodeficiency virus infection (Chronister, 2000), rheumatoid arthritis

(Squirrell et al., 1999) or carcinoma (Sridhar et al., 2001), have a higher risk of

contact lens-associated microbial keratitis. Wong et al. (1997) reported a total 21%

of keratomycosis were present in patients with systemic immunosuppressive

disease.



Poor compliance in lens hygiene is another major risk factor in contact

lens-associated microbial keratitis (Leisegang, 1997b; Houang et al., 2001;

Weissman and Mondino, 2002; Stapleton, 2003). Up to 91% of contact lens

wearers show some degree of non-compliance with the care of their contact lenses

(Collins and Carney 1986, Chun and Weissman 1987, Sokol et al. 1990, Turner et

al. 1993a, Turner et al. 1993b, Gower et al. 1994, Ky et al. 1998) (See Section 3.1).

This allows microorganisms to colonize on lenses and gain access to the eyes.




                                                                              24
                                                                           Chapter 2


Other potential risk factors of contact lens-associated microbial keratitis include:

the use of steroids, chlorine-based disinfectants, one-step hydrogen peroxide

disinfectants, lack of proper disinfection, swimming with contact lenses, rinsing

contact lenses with non-sterile solutions, letting tap water come into contact with

lenses or storage cases, lower socioeconomic class, the male gender, smoking and

travel to warm climates (Radford et al., 1995; Leisegang, 1997a; Radford et al.,

1998; Houang et al., 2001; Radford et al., 2002; Weissman and Mondino, 2002;

Stapleton, 2003).



2.3.1          Summary

Predisposing factors for contact lens-associated microbial keratitis have been

studied extensively. Major risk factors include: EW of contact lenses, corneal

trauma, blepharitis, systemic immune compromise and poor compliance in the use

of contact lenses. Other minor predisposing factors are mainly related to improper

use and care of contact lenses, lower socioeconomic class, male gender, smoking

and travel to warm climates.




                                                                             25
                                                                       Chapter 2



2.4    Physiological changes associated with contact lens
       wear

Contact lenses not only act as a vector introducing microorganisms into the eye

(Aswad et al., 1990; Willcox and Holden, 2001), they also increase the risk of

microbial keratitis by compromising the cornea during contact lens wear. Contact

lens wear induces a series of physiological changes, including alteration of the

ocular flora (Callendar et al., 1986; McClellan et al., 1998), changes in tear

components (Jones and Sack, 1990; Thakur and Willcox, 2000), hypoxia and

hypercapnia and reductions in pH (Bonanno and Polse, 1987a and 1987b; Rivera

and Polse, 1996), metabolic rate (Wilson 1994; Ladage et al., 2003; Cavanagh

2003) and corneal sensitivity (Sanaty and Temel, 1998; Toil et al., 2003). These

physiological changes can involve all layers of the cornea (Holden and Sweeney,

1985a).



2.4.1 Alteration of ocular flora

Normal bacterial floras play an important role in the prevention of infectious

disease, any change in the balance of the microbial environment resulting in an

increased risk of disease (Saigh et al., 1978; MacDonald and Pettersson., 2000).

Common components of the ocular flora are usually non-pathogenic but some are

opportunistic pathogens and can cause microbial keratitis in patients with a

compromised defence system (Parkin et al., 1997; Wang et al., 1998). Common

flora found in the conjunctiva, eyelid and tears include Achromobacter, Bacillus

spp., Corynebacterium spp., Diphtheroids, Flavimonas spp., Flavobacterium,

Haemophilus spp., Lactobacillus, Micrococcus spp., Moraxella spp., Neisseria,

Peptostreptococcus spp., Propionbacterium spp., CNS, Staphylococcus, and


                                                                         26
                                                                           Chapter 2


Stenotrophomonas (Callender et al., 1986; Elander et al., 1992; Fleiszig and Efron,

1992; Willcox et al., 1997; Higaki et al., 1998).



The effect of contact lens wear on the ocular flora has been studied extensively.

Hovding (1981) examined conjunctival cultures of 113 contact lens wearers and

99 non-wearers and claimed that the contact lens wearers were less likely to be

contaminated. More recent studies had shown there is no significant difference in

the frequency of bacteria isolated from contact lens wearers and non-wearers.

Callendar et al. (1986) found no significant difference in the number of bacteria in

the tear fluid of contact lens wearers and non-contact lens wearers but they

reported that there were twice as many bacterial species isolated from the contact

lens wearers. In the studies of Elander et al. (1992), Fleiszig and Efron (1992) and

McClellan et al., (1998), bacteria isolated from the conjunctiva sac of contact lens

wearers were similar to those of the non-wearers. Elander et al. (1992) also

reported that there was no difference in conjunctival flora between pre- and

post-lens wearing eyes after one week of contact lens wear. Similar results were

obtained by Higaki et al. (1998), who found no significant difference between the

frequency of bacteria isolated from aphakic eyes of 26 subjects (wearing EW

contact lenses) and the fellow eyes (without contact lenses). In contrast, the

binding of P. aeruginosa to exfoliated corneal epithelial cells was significantly

increased after DW of both conventional soft and SH lenses (Ladage et al., 2001).

Most studies have shown that contact lens wear does not greatly alter the number

of conjunctival flora; however, some studies show contradictory results. The

differences among these studies may result the use of various lens disinfecting

regimens (Hovding, 1981; Fleiszig and Efron, 1992), the durations of lens wear



                                                                             27
                                                                           Chapter 2


(Hovding, 1981; Fleiszig and Efron, 1992; Hart et al., 1996) and lens compliance

(Fleiszig and Efron, 1992), as these factors may influence the number and species

of conjunctival flora. As alterations in microflora may be important etiologic

factors in the development of microbial keratitis, more research is required in this

area.



2.4.2 Changes in tear components

Tears remove microbes from the ocular surface and distribute antimicrobial agents

such as lysozyme, immunoglobulins, lactoferrin and betalysin over the ocular

surface through blinking (McClellan, 1997), however, the amount of these

antimicrobial agents in tears is altered by the presence of contact lenses and their

mode of wear.

The amount of secretory IgA in tears is significantly reduced among contact lens

wearers when compared with non-contact lens wearers (Willcox and Lan, 1999).

Reductions of 60% and 70% in the tear Ig A was found for DW and EW contact

lens wearers, respectively. Thakur and Willcox (2000) also found that the number

of polymorphonuclear leukocytes in tears was altered after one overnight wear of

contact lens and these changes were dependent upon the contact lens experience of

the lens wearers. Significantly higher numbers of polymorphonuclear leukocytes

was found in the tears of non-adapted contact lens wearers after one night of

overnight contact lens wear when compared with adapted contact lens wearers

(Thakur and Willcox, 2000)




                                                                             28
                                                                         Chapter 2



2.4.3 Hypoxia and hypercapnia


The avascular cornea obtains oxygen and releases carbon dioxide through gaseous

exchanges with the atmosphere via the tears. These gaseous exchanges are

disrupted during contact lens wear, as the cornea is isolated from the atmosphere.

Hypoxia describes the reduction of oxygen available to the cornea, whereas

hypercapnia represents the accumulation of carbon dioxide during contact lens

wear (Bruce and Brennan, 1990). The amount of oxygen available to the cornea

during contact lens wear is directly associated with the oxygen permeability (Dk)

and inversely associated with the thickness (t) of the contact lenses. The oxygen

tension required by the cornea for maintenance of its normal functions was

reported to be 74 mmHg (Holden et al., 1984; Brennan et al., 1987). Wearing

contact lenses with Dk/t below 70 X 10-9 (cm/sec)(ml O2/ml mmHg), a linear

relationship was found between oxygen tension and Dk/t of the lenses (Ichijima et

al., 1998); wearing contact lenses with higher Dk/t, oxygen tension gradually

increases with the Dk/t of the lenses and approaches the saturation level at 120

mmHg under opened eye condition (Ichijima et al., 1998).

Ang and Efron (1990) measured the extent of corneal hypoxia and hypercapnia

with different Dk/t contact lenses under both static (open-eye and closed-eye) and

dynamic (with blinking) conditions. They reported hypoxia and hypercapnia were

reduced significantly with the increased Dk/t of contact lenses, whereas blinking

helps to reduce the level of hypoxia but not hypercapnia.

Galvin et al. (2000) compared corneal hypoxic responses under lens wear and

normal conditions without contact lenses (lowest hypoxia response). They found

that even with high Dk/t [91 x 10-9 (cm/sec)(ml O2/ml mmHg)] contact lenses,




                                                                           29
                                                                            Chapter 2


corneal hypoxic responses was found to be 1.5 and 2.7 times higher than normal

with eyes open and closed, respectively.

Hypoxia and hypercapnia induced by contact lens wear suppress corneal aerobic

metabolism and stimulate anaerobic glycolysis (Bonanno and Polse, 1987a and

1987b). These induce a series of unwanted consequences, including decreased

corneal pH, corneal neovascularization, decreased corneal metabolic rate and

reduction in corneal epithelial thickness, stromal oedema and endothelium defects.



2.4.4 Reduced corneal pH

Corneal stromal pH decreased from 7.55 ± 0.02 to 7.15 ± 0.04 after wearing

contact lenses with low Dk/t (2.4 x 10-9 (cm/sec)(ml O2/ml x mmHg)) for 80

minutes with eyes open (Bonanno and Polse, 1987b). Rivera and Polse (1996)

studied how hypoxia and hypercapnia induced stromal acidosis by exposing

contact lens wearing eyes to hyperbaric (80% oxygen and 20% nitrogen) and

normal atmospheric conditions (20% oxygen and 80% nitrogen). Wearing low

Dk/t lenses for 120 minutes under hyperbaric condition produced a decrease in

corneal pH (0.23 ± 0.05) but no increase in corneal thickness (no hypoxic effect).

In contrast, a greater decrease in pH (0.62 ± 0.48), together with an increase in

corneal thickness (hypoxic effect), were recorded after exposure of the cornea to

atmospheric conditions similar to air. This indicates that stromal acidosis is

induced by hypoxia in addition to hypercapnia.

The reduction in pH is due to increased corneal anaerobic glycolysis and drainage

difficulties across the cornea under hypoxic conditions (Imre, 1984). Therefore,

the change in pH is affected by individual metabolic requirements and the

transmissibility of the lenses (Rivera and Polse, 1996; Ichijima et al., 2000).


                                                                              30
                                                                             Chapter 2


Following the decrease in corneal pH, there is an increase in osmotic load within

the corneal stroma, which results in fluid uptake into the stroma and corneal

oedema (Klyce, 1981; Huff, 1990). However, this fluid uptake is not evenly

distributed across the cornea. The posterior lamellae of the stroma can reach a

higher level of hydration than the anterior lamellae, resulting in greater swelling in

the posterior lamellae (Meek et al., 2003). Corneal oedema is inversely correlated

with tear oxygen tension and directly correlated with changes in stromal pH

(Bonanno and Polse, 1987a and 1987c). Therefore, it is not hard to understand

why thicker corneas were found in patients wearing hydrogel lenses on an EW

basis, as more severe hypoxia is associated with overnight wear (Pall et al., 2003).

In addition to corneal oedema, a prolong increase in lactic acid concentration in

the   avascular   cornea    stimulates    the   development      of   deep    stromal

neovascularization. Although large deep intracorneal haemorrhage associated

with new vessels are rare, there are reports of visual loss associated with deep

stromal neovascularization after improper contact lens wear (Rozenman et al.,

1989; Wong et al., 2003).



2.4.5 Corneal epithelial changes

The metabolic rate of the corneal epithelium is increased during contact lens wear.

Tsubota and Laing, (1992a) measured the epithelial pyridine nucleotides/oxidized

flavoproteins (PN/Fp) ratio, an indicator of metabolic status, and found that the

epithelial metabolic rate increases with the wearing of contact lenses. They

reported that the change in epithelial metabolic rate depends on the Dk of the

contact lenses; a large increase in PN/Fp was observed with low Dk lenses (Dk =

12.5), whereas wearing highly oxygen-permeable contact lenses (Dk = 58.8) did



                                                                               31
                                                                             Chapter 2


not change this ratio. This increase in PN/Fp ratio indicates an inhibition of

respiration due to the contact lens and a shift from aerobic to anaerobic

metabolism in the corneal epithelium.

Corneal epithelial thinning also occurs with contact lens wear. A 6% reduction in

epithelial thickness and a 2.3% reduction in stromal thickness were recorded in 27

subjects after 62 ± 29 months EW of soft contact lenses when compared with their

fellow eyes without lenses (Holden et al., 1985b). The thinning of the epithelium is

a reversible process and epithelial thickness recovers after cessation contact lenses

wear (Holden et al., 1985b). The thinning of the corneal epithelium may be due to

a reduction in cell proliferation (Holden et al., 1985b; Cavanagh, 2003) after

chronic hypoxia. There are also reports of a decrease in epithelial cell exfoliation,

epithelial adhesion (Madigan and Holden, 1992) and flattening and enlargement of

the remaining epithelial cells (Tsubota and Yamada, 1996; Ladage, 2001) after

contact lens wear (Wilson 1994; Ladage et al., 2001). Contact lens wear also

disrupts the corneal epithelium by inducing abrasion, with associated staining, due

to breakdown of the epithelial surface (Nichols et al., 2002). The presence of

corneal staining associated with contact lens wear is due to mechanical irritation,

destabilizing the pre-lens tear film, dehydration of the lens surface and solution

toxicity (Guillon et al., 1990; Jalbert et al., 2001; Jones et al., 2002).

All of these physiological changes to the epithelium weaken its function as the first

physical barrier to penetration of microbial pathogens and increase the risk of

infection (Bergmanson, 1987).




                                                                               32
                                                                            Chapter 2



2.4.6 Corneal endothelial changes

Contact lens wear also induces endothelial changes, such as transient blebs and

permanent polymegethism and pleomorphism, which changes are related to

disturbances of corneal endothelial metabolism (Vannas et al., 1984).

Polymegathism and pleomorphism are common morphologic changes observed

during both hard and soft contact lens wear (Stocker and Schoessler, 1985; Holden

et al., 1985b; Matsuda et al., 1988; Esgin and Erda, 2002). It has been suggested

that these endothelial changes indicate the endothelial compromise under hypoxic

stress during contact lens wear (Matsuda et al., 1988). As the endothelium

regulates fluid uptake by the cornea (Nguyen et al., 2003), any disruption of

metabolism of this layer further enhances corneal swelling. Giasson and Bonanno

(1995) reported that the pH of corneal endothelial cells was significantly reduced

by contact lens wear and that this pH change is mainly caused by hypercapnia

behind the contact lenses. These endothelial changes are more long-lasting than

those occurring in the epithelial layer (Holden et al., 1985b).



2.4.7 Corneal sensitivity

Corneal sensitivity which is associated with corneal thickness (du Toit et al., 2003)

was also decreased by contact lens wear. Sanaty and Temel (1998) evaluated

corneal sensitivity of 20 PMMA wearers who had worn contact lenses for up to 20

years. They reported a significant reduction of corneal sensitivity among contact

lens wearers. A greater reduction of corneal sensitivity was found in the central

cornea and the extent of sensitivity loss was related to the duration of contact lens

wear. The decrease in corneal sensitivity may be related to the observed changes in

corneal innervation and the decrease in both the density and function of



                                                                              33
                                                                              Chapter 2


endothelial cells (Bergmanson, 1987; Nguyen et al., 2003). Corneas with lower

sensitivity have a higher risk of severe infection, as the ability to detect the initial

symptoms is reduced.



2.4.8 Summary

Contact lens wear induces a wide range of corneal physiological changes. These

include alteration of the ocular flora, changes in tear components, hypoxia,

hypercapnia, increased corneal anaerobic metabolism and reduced corneal

sensitivity. These physiological changes induce many unfavourable corneal

responses. They disrupt the balance of corneal metabolism and weaken its defence

mechanisms. In general, complications associated with contact lens wear are

correlated inversely with lens Dk (Perez et al., 2003) and directly with continuous

wearing time (Tsubota et al., 1996). Being compromised by contact lens wear, the

cornea is more susceptible to microbial infection.




                                                                                 34
                                                                              Chapter 3




Chapter 3
Contamination of contact lenses and
lens care accessories

Contact lens wear has been recognized as an important risk factor for the

development of microbial keratitis, especially when they are used on an EW basis

(Chalupa et al., 1987; Nilsson and Montan, 1994b; Weissman and Mondino, 2002;

Stapleton, 2003). Contaminated contact lenses were suggested to be the vector

transporting pathogens into the eyes, and epidemiological studies have shown that

keratitis inducing pathogens did not only isolate from the corneas but also from

contact lenses and lens cases used by patients (Martins et al., 2002; Bourcier et al.,

2003).


Table 3.1 Percentage of contact lens-associated microbial keratitis, positive culture
of corneal scrapes, and contact lenses or lens cases.

                                       Microbial
                                                       Corneal scrapes   Contact lenses or
                                       keratitis
                                                        with positive     lens cases with
                                    associated with
                                                           culture        positive culture
                                   contact lens wear
Cohen et al., 1996       US              30%                  -                  -

Houang et al.,       Hong Kong           26%                36%                  -
2001

Schaefer et al.,     Switzerland         36%                  -                  -
2001

Martins et al.,        Brazil              -                33%                47%
2002

Bourcier et al.,       France           50.3%               63%                84%
2003

Mela et al., 2003      Greece            27%                43%                86%




                                                                                     35
                                                                              Chapter 3


In published reports, positive cultures of corneal scrapings were obtained from

33% to 63% of contact lens-associated microbial keratitis patients (Alexandrakis

et al., 2000; Houang et al., 2001; Bourcier et al., 2003; Mela et al., 2003) (Table

3.1). This low percentage of positive corneal culture was due to patients who

usually had received certain topical antibiotic treatment before corneal scrapes

were taken (Houang et al., 2001).

In a 24-year retrospective study carried out by Martins et al. (2002) on 113 contact

lens-associated microbial keratitis patients, up to 84% concordance was found

between the cultures obtained from their corneal scrapings and contact lenses.

However, in another study by Bourcier et al. (2003), they only found similar

organisms from corneal scraping and contact lenses/lens cases in 21% (14/67) of

cases. Although the percentage of matching microorganisms found from corneal

scrapings and contact lenses varies between studies, the results of these studies

showed certain existing concordances between the cultures obtained from corneal

scraps and contact lenses/lens cases. Some investigators suggested the cultures of

swabs of contact lens, lens cases and lens storage solutions to be included (in

addition to corneal scraping) in the diagnosis of infectious keratitis (Martins et al.,

2002; Mela et al., 2003). This was suggested to improve the yield of infectious

pathogens leading to keratitis and allow the use of the most appropriate therapy,

especially for those patients that have negative results from their corneal culture. It

has also been suggested that treatment with topical steroids prior to corneal culture

should also be avoided, as it makes the identification of pathogens more difficult

and increases the risk of poor prognosis of contact lens-associated microbial

keratitis (Miedziak et al., 1999).




                                                                                    36
                                                                                    Chapter 3


In order to have better understanding about the etiology of contact lens-associated

microbial keratitis, previous reports on the contamination of contact lenses, lens

cases and lens care solutions were reviewed.


3.1 Contamination of contact lenses

Large variations in the contamination rate of contact lenses have been reported in

previous studies. Reports of the contamination rates of contact lenses from

asymptomatic contact lens wearers ranged from 38% to 84% (Hart et al., 1993;

Lipener et al., 1995; Velasco and Bermudez, 1996) (Table 3.1.1).


Table 3.1.1. Contamination rates of contact lenses, lens case and solutions reported
by previous investigators.

                                                        Contact
                                         N                          Cases          Solutions
                                                         lenses
                                 38 rigid & 62 soft
                                                           -         46%              13%
Donzis et al.,                  contact lens wearers
                      US
1987
                                62 soft contact lens
                                                           -         43%              26%
                                      wearers

Devonshire et                    46 rigid & 132 soft
                    Scotland                               -         53%                 -
al., 1993                       contact lens wearers

Hart et al.,                    49 soft contact lens
                      US                                 38%           -                 -
1993                                  wearers

Gray et al.,         New         15 rigid & 86 soft
                                                           -         81%                 -
1995                Zealand     contact lens wearers

Rosenthal et al.,                 110 contact lens
                      US                                             25%
1995                                  wearers

Lipener et al.,                 15 soft contact lens                                   60%
                     Brazil                              80%         87%
1995                                  wearers                                    (tips of bottles)

                                  1 rigid & 20 soft                   24%
Midelfart et al.,
                    Norway      contact lens wearers       -      (solution in           -
1996
                                  (medical students)                 case)
Velasco and
                                126 soft contact lens
Bermudez,            Spain                               84%         81%              63%
                                      wearers
1996
Sweeney et al.,                 40 soft contact lens                             26% Contents
                    Australia                              -           -
1999                                  wearers                                    55% Nozzies




                                                                                             37
                                                                          Chapter 3


Hart et al. (1993) studied the contamination rate of 108 soft contact lenses

collected from 49 asymptomatic contact lens wearers. Each contact lens was

removed by hand wearing sterile glove. Lens extract was made by immersing

lenses removed from eye in 3ml of 0.1% sterile peptone water and agitated with

vortex mixer. After that, contact lens and lens extract were cultured separately.

Lens extract was inoculated onto 5% sheep blood agar (BA), Sabouraud dextrose

agar (SDA) and tryptic soy agar (TSA), whereas the contact lens was cultured in a

TSA sandwich agar. Contaminants, all bacteria, were found in 38% (41) of the

contact lenses, 39 from lens extracts, eight from both lens extracts and contact

lenses, and two from contact lenses only. Hart et al. (1993) concluded that most

contaminants were only transiently associated with the contact lenses, only a few

of them were firmly attached to contact lenses, as most bacteria could be isolated

from lens extracts and only two samples yield positive cultures from contact lenses

but not from lens extracts. S. epidermidis and E. coli were the most frequently

isolated bacteria from lens extracts and contact lenses respectively.



In another contamination study carried out by Lipener et al. (1995), 30 contact

lenses were removed from the lens cases rather than from the eyes. Lenses were

collected from 15 contact lens wearers but no information regarding how the

lenses were cultured was given in this study. Contaminants were isolated from

80% (24) of contact lenses and mixed floras were found in 33.3% of positive

cultures. The contamination rate reported in this study was much higher than that

compared with Hart et al. (1993). This may be because in Lipener et al.’s study

contact lenses were collected from the lens cases rather than from the eyes. Other

reasons contributing to the higher contact lens contamination rate found by



                                                                                38
                                                                            Chapter 3


Lipener et al.be may due to the limited subject number and different culturing

method used. Major contaminants found in this study were S. aureus and

Pseudomonas spp.



Velasco and Bermudez (1996) studied the contamination of 252 contact lenses

collected from the eyes of 126 asymptomatic contact lens wearers.

Polyhydroxyethyl methacrylate contact lenses (55% water content) and

polyaminopropyl biguanide maintenance solutions together with lens care

instructions were given to all subjects at the beginning of the study. Contact lenses

were cultured after being worn for 270 days. Both surfaces of the lenses were

swabbed with sterile cotton swabs moistened with sterile, unpreserved saline.

Eighty four percent (212) of contact lenses were found to be contaminated. This

was again much higher than those reported in Hart et al.’s study (38%). Velasco

and Bermudez suggested that high contamination rate was due to failure in

following hygiene instructions and inadequate personal hygiene among their

subjects. According to their observation, high proportions of subjects were using

dirty lens cases, had dirty fingernails and did not bathe regularly. Some subjects

were also suspected to top up lens care solutions for several disinfections. Major

contaminants isolated from contact lenses in this study included S. epidermidis

(24%), S. aureus (17%), Streptococcus viridans (13%) and P. aeruginosa (12%).



To summarize, the contamination rate of contact lenses of asymptomatic lens

wearers reported in the literatures ranged from 38% − 84%. Contact lenses could

be contaminated by a wide range of microorganisms, and some potential

pathogens of microbial keratitis could also be isolated from contaminated contact



                                                                                  39
                                                                          Chapter 3


lenses. Common contaminants associated with contact lenses included S.

epidermidis, S. aureus, Streptococcus. viridans and P. aeruginosa.



3.1.1 Sources of contact lens contaminants

From the results of previous studies (Hart and Shih, 1987; Mowrey-McKee et al.,

1992), it had been demonstrated that patients-handled contact lenses were more

frequently and heavily contaminated than patients-worn contact lenses.

Hart and Shin (1987) compare microorganisms isolated from 25 pairs of

patient-worn contact lenses and 4 pairs of patient-handled contact lenses. They

reported only one pair of patient-worn contact lenses (1/25) was associated with

contaminants, whereas all (4/4) patient-handled contact lenses were contaminated.

Similar results were reported in a later study carried out by Mowrey-McKee et al.

(1992). They compared contamination rates and contaminants associated with

patients-worn and patient-handled contact lenses collected from 20 subjects. They

reported 43% (17/40) of patient-worn contact lenses and all (40/40)

patient-handled contact lenses were being contaminated. The numbers of colonies

isolated from patient-worn contact lenses were significantly lower than

patient-handled contact lenses. Most contaminants isolated were mainly bacteria,

and fungi were only found from patient-handled contact lenses but not from

patient-worn contact lenses.

The results of these studies demonstrate that contaminations of contact lenses were

highly associated with patient handling of the lenses and most contaminants are

usually only transiently associated with the lenses and could be removed by tears

and blinking action during lens wear.




                                                                                40
                                                                             Chapter 3


In another study carried out by Willcox et al. (1997), they studied the source of

contact lens contaminants by comparing microorganisms colonized on contact

lenses with those isolated from a few potential sites including: lower lid margins,

upper bulbar conjunctiva, hands, contact lens cases and domestic water supply.

They reported that the two most likely sources of contaminants found on contact

lenses were the lower lid margin or the domestic water supply, as bacteria isolated

from the lower lid margin and domestic water supply were correlated with those

isolated from contact lenses. Contaminants associated with the lower lid margin

were usually normal skin flora, whereas potential microbial keratitis-inducing

pathogens were found from domestic water supply. Although no correlation was

found between microorganisms isolated from contact lenses and other test sites,

Willcox et al. suggested that other sites might also contributed to the

contamination of contact lenses, but the level did not reach statistical significance.



3.1.2 Factors contributing to the contamination of contact lenses

Many factors contribute to the adhesion of bacteria on contact lens surfaces.

Contaminants and contaminations of contact lenses vary with lens material, lens

deposits and wearing schedule (Miller and Ahearn, 1987; Willcox et al., 2001).



3.1.2.1      Lens materials

The adhesion ability of bacteria to contact lens surfaces varies with different types

of lens polymer. From previous studies, it has been demonstrated that the

attachment of bacteria is affected by the ionic charge and water content of contact

lens material (Miller and Ahearn, 1987; Dang et al., 2003).




                                                                                   41
                                                                             Chapter 3


Table 3.1.2. Soft contact lens properties of different groups of lens polymers.


Group             Ionic charge     Water content                  Examples

                                                               Tefilcon (37.5%)
I                  Non-ionic           < 50%                  Polymacon (38.6%)
                                                             Tetrafilcon A (42.5%)
                                                               Vifilcon A (55%)
II                 Non-ionic           > 50%                  Alphafilcon A (66%)
                                                              Lidofilcon A (70%)
                                                              Phemfilcon A (38%)
III                  Ionic             < 50%
                                                               Bufilcon A (45%)
                                                               Bufilcon A (55%)
IV                   Ionic             > 50%                  Phemfilcon A (55%)
                                                               Etafilcon A (58%)



A summary of the different groups of soft contact lens polymers, according to The

Food and Drug Administration is shown in table 3.1.2. Miller and Ahearn (1987)

reported non-ionic polymer (Group I and II polymers) showed a higher attachment

of bacteria than ionic polymers when tested with different types of P. aeruginosa.

Their results were only partly agreed by Dang et al. (2003), who showed that the

highest attachment of P. aeruginosa was with high water non-ionic lenses (Group

II polymer). Dang et al. (2003) reported that ionic lenses (Group III and IV

polymers) showed intermediate level of P. aeruginosa binding and the lowest

attachment was with lower water non-ionic lenses (Group I polymer). Miller and

Ahearn (1987) also reported that the adherence of bacteria varied with

experimental time, pH and electrolyte concentration. The adherence of bacteria

was found to increase with experimental time; and the greatest number of adhered

bacteria was observed at pH7 and at a saline concentration of 50mM.




                                                                                     42
                                                                           Chapter 3


3.1.2.2        Lens wear and lens deposits

There are studies reporting differences in bacterial adhesion between worn and

unworn contact lenses. However the effect of lens wear on bacterial adhesion

varied with lens materials, and that the adhesion of bacteria on balafilcon A lenses

increased after lens wear (Willcox et al., 2001); whilst the adhesion of bacteria

decreased after etafilcon A lenses has been worn (Willcox et al., 2001; Bruinsma

et al., 2002). These changes in bacterial adhesion were suggested to be associated

with the changes in physicochemical properties of the lens surfaces, after the

absorption of organic compounds during contact lens wear (Bruinsma et al., 2001

and 2002). Within 10 days of lens wear, the adhesion of bacteria was found to

change according to lens surface hydrophobicity, roughness, the presence of

nitrogen-rich material and oxygen-rich material on lens surface. However after 50

days of lens wear, the adhesion of bacteria changed mainly according to roughness

and the presence of tear lipocalin (Bruinsma et al., 2002). These changes in lens

surface properties and bacterial adherence may be explained by the accumulated

protein deposits on lens surface.

From the study by Hart et al. (1993), contact lens contamination was found more

likely to be associated with deposits and abnormal coating on lens surfaces. They

suggested that deposits serve to provide nutrients and attachment of bacteria.

Using radiolabeling technique and electron microscopy, Aswad et al. (1990)

reported the adhesion of bacteria was proportional to the number of focal deposits.

Bacteria adhered primarily to large focal deposits and only little adherence were

observed at the areas in between focal deposits (Aswad et al., 1990). The

accumulation of protein deposit was also found to be related to the length of lens




                                                                                 43
                                                                            Chapter 3


wear and the lens polymer (Miller and Adearn, 1987; Michaud and Giasson,

2002).

Jones and Sack (1990) reported a heavier deposition of immunoglobulins with the

use of high water contact lenses on EW basis. These heavier depositions of

immunoglobulins were resulted by a greater degree of immune stress with the use

of contact lenses on an EW basis (Jones and Sack, 1990). Group II contact lenses

have also been demonstrated to have a higher capacity for the accumulation of

protein and lipid deposits than worn Group IV lenses (Jones et al., 2000), and this

may be the reasons why Group II contact lenses were more favourable for bacterial

adhesion than other group of contact lenses.



3.1.2.3        Biofilm formation

In an experimental study carried on contact lenses pre-coated with a mixture of

protein (lactoferrin, lysozyme, γ-globulins, albumin and mucin), it was shown that

bacteria adhered on lens surfaces were able to grow and form biofilms (Willcox et

al., 2001). Using electron microscopy, biofilm could be visualized on contact

lenses from contact lens wearers with microbial keratitis (McLaughlin-Borlace et

al., 1998). Normally bacteria were only transiently adhered to lens surfaces and

could be removed by blinking during lens wear (Hart and Shin, 1987;

Mowrey-McKee et al., 1992). However in the presence of biofilm, the attachment

of bacteria on lens surface became firmer. Biofilm provided physical protection

againt disinfectants, and allowed survival and replication of microorganisms

(Elder et al., 1995). Bacteria shielded within a fully developed biofilm were 2 to

3000 times more resistant to disinfectant than planktonic cells (LeChevallier et al.,

1988). It has been suggested that this increased resistance to disinfectants was due



                                                                                  44
                                                                             Chapter 3


to the limited access of disinfectants to bacteria within the biofilm (LeChevallier et

al., 1988).

Bacteria associated with contaminated contact lens care systems also served as a

food source for acanthamoeba (Bottone et al., 1992). This allowed contaminated

contact lenses and lens cases, especially those coated with biofilm, to become

more favourable for the survival of acanthamoeba (Bottone et al., 1992). The

presence of biofilm also increased the risk of microbial keratitis as it prolonged the

exposure of pathogens to cornea (Elder et al., 1995; McLaughlin-Borlace et al.,

1998), as the biofilm protected them from being removed by blinking.



3.1.3   Summary

The results of these studies indicate that contact lenses can be contaminated by a

wide diversity of microorganisms present in different sites, especially those

colonized on lid margin and domestic water supply. These contaminants are most

likely to be transmitted to the contact lenses through contact with hands or facial

skin during contact lens handling, lens insertion or lens removal. Bacterial

adhesion depends on the micro-environment changes on the lens surface after lens

wear and therefore it varies between different lens materials. In general high water

non-ionic (Group II) polymer is more favourable for the attachment of bacteria

(Miller and Ahearn, 1987; Dang et al., 2003). The level of bacterial adherence is

proportional to the level of protein deposits. Bacteria adhered on lens surfaces can

grow and coalesce together and form biofilms. Biofilm increases the potential

pathogenicity of pathogenic microorganisms by shielding them from disinfectants

and prolonging contact of bacteria to the cornea. Improved strategies for the

control of deposits and biofilm on lens surface are therefore important to reduce



                                                                                   45
                                                                           Chapter 3


the contamination of contact lenses and to prevent the occurrence of microbial

keratitis.



3.2 Contamination of lens cases

Similar to contact lens contamination, there were also large variations in the

contamination rate of lens cases. Reports of contamination rates of lens cases

range from 24% to 87% (Donzis et al., 1987; Devonshire et al., 1993; Gray et al.,

1995; Lipener et al., 1995; Rosenthal et al., 1995; Midelfart et al., 1996; Velasco

and Bermudez, 1996). Among contact lenses, lens cases and lens care solution,

lens cases are usually found to be the most frequently contaminated and are

associated with a wider range of species of microorganisms (Donzis et al., 1987;

Lipener et al., 1995).

Donzis et al. (1987) investigated the contamination rate of 94 lens cases collected

from 100 (38 rigid lens wearers and 62 soft lens wearers) asymptomatic patients.

They collected solution inside the lens cases with a cotton swab and tested for

contamination. If there was no solution inside the case, a cotton swab moistened

with sterile, unpreserved saline was used to swab the interior surfaces of the case.

Collected samples were inoculated onto BA and anaerobic BA for bacterial

isolation, fungal cultures were carried out with Sabhi agar and acanthamoeba

cultures were carried out with nonnutrient agar overlaid with E. coli. They found

that 46% (43) of tested lens cases were contaminated. They reported that CNS was

the most commonly isolated microorganisms, whereas other skin flora such as S.

epidermidis; and gastrointestinal tract flora such as Enterobacter, Serratia, and

Klebsiella were also isolated. No acanthamoeba was cultured from the tested lens

cases.



                                                                                 46
                                                                             Chapter 3


In agreement with Donzis et al. (1987), Devonshire et al. (1993) found similar

contamination rate of lens cases. They reported that 53% (95) of lens cases

collected from 178 asymptomatic contact lens wearers were contaminated. They

first transferred all solution inside the lens cases to a sterile universal container;

then a sterile cotton wool swab moistened with sterile saline was used to swab the

interior surfaces of the case vigorously. The tip of the swab was then added to the

universal container with the collected solution. Contents inside the universal

container was vortexed and mixed for 10 seconds and then used for microbial

examination. The same procedures were also applied to dry lens cases. Both

bacterial and amoebal contaminations were assessed. Bacterial cultured with BA

and cystine lactose electrolyte deficient (CLED) agar. Amoebal isolation was also

carried out using nonnutrient agars overlaid with E. coli. Serratia and

Pseudomonas spp. were the most common contaminants isolated from lens cases.

Potential microbial keratitis-inducing pathogens were isolated from 25% (33) of

lens cases used by soft contact lens wearers. They reported the presence of

acanthamoeba and yeast in 4.5% (6) and 0.75% (1) of lens cases. Acanthamoeba

was always found to be associated with the presence of at least one of the

following bacteria ⎯ Enterobacter agglomerans, Flavobacterium indologenes,

Pseudomonas fluorescens, Serratia marcescens and Klebsiella pneumoniae.



In the study carried out by Gray et al. (1995), they cultured lens cases with a

method similar to the one used by Devonshire et al. (1993). They cultured 101

lens cases using a sterile cotton wool swab to swab the internal surface of each

case. The case was then filled with 4ml of sterile saline and shaken vigorously.

The case extract and the tip of the cotton wool swab were then mixed with a vortex



                                                                                   47
                                                                          Chapter 3


for 10 seconds in another container before microbial evaluation. Bacteria were

isolated with BA and MacConkey agar and fungi were isolated with SAC slope

(SDA with 0.1% chloraphenicol and 0.4% gentamicin). Amoebal culture was

carried out with Pages amoeba saline agar overlaid with dead E. coli. In agreement

with other studies, most lens cases (77%) were contaminated by bacteria. A higher

isolation of fungi was reported in this study ⎯ 24 fungal contaminants were

isolated from the lens cases. They reported isolations of Cladosporium spp.,

Candida spp., Fusarium solani, Asperigllus versicolor, Exophiala spp. and Phoma

spp. Beside Acanthamoeba, other protozoa such as Naegleria spp., Vahlkampfia

and Hartmannella spp. were also isolated from lens cases. Gary et al. reported that

their results could be biased by the inclusion of a large proportion (71%) of

one-step hydrogen peroxide users. Since studies had shown that one-step

hydrogen peroxide system was found to be less effective in disinfection and

microorganisms were found able to survive on the platinum disk of the one-step

hydrogen peroxide system (Gary et al., 1999) (see Section 3.1.3.1); the inclusion

of a large proportion of one–step hydrogen peroxide users was therefore

contributing to the high contamination rate found in this study.

In the study by Lipener et al. (1995), a sterile cotton wool swab was used to touch

the inside part of the case, and then the culture medium. A total 87% of lens cases

were found to be contaminated and 30.7% of lens cases were associated with

mixed contaminants. The high contamination rate found in this study may be due

to small subject number (N=15) and since details on how the cultures were

performed in this study were not given, it was uncertain if culture method differed

from other studies. In this study, P. mirabilis was the most common contaminants

isolated from lens cases followed by S. aureus and P. aeruginosa.



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                                                                            Chapter 3


Rosenthal et al. (1995) and Midelfart et al. (1996) only found 24% − 25% of

contaminated lens cases. In Rosenthal et al.’s study, they used a different method

for the culture of 110 lens cases. Collected lens cases were rinsed, emptied and air

dry before sending to the laboratory, and cultures of lens case was done within 72

hours. The case chambers were first filled with sterile soybean-casein digest broth

and then each chamber was scrapped with a sterile inoculating loop. After that, the

case chambers were closed and shaken gently, this case suspension was then use

for the culture of contaminants. Common contaminants isolated from the lens

cases   included   Bacillus    spp.,   Enterococcus    spp.,   Strepococcus     spp.,

Corynebacterium spp., Pseudomonas spp., S. marcescens, Staphylococcus spp.,

Xanthomonas malthophilia, Acremonium spp., and C. parapsilosis. The low

contamination rate of lens cases reported in this study may be due to the difference

in the method of sample collection. Collected lens cases were kept dry for a long

time (maximum up to 72 hours) before they were cultured. This was likely to result

in a reduction in the yield of microorganisms and thus an underestimation of case

contamination.



The study carried by Midelfart et al. (1996) asked subjects (all medical students) to

collect the lens care solutions inside the lens case, after soaking contact lenses

overnight and before contact lens insertion in the next morning. The sample of lens

care solution was collected using sterile pipette and stored in sterile container

before microbial examination. The contamination rate of the collected solutions

was presented as the contamination rate of the lens cases. A much lower lens case

contamination rate (24%) was reported. Contaminants shielded inside biofilm

built up on the interior surface of the case chamber may not have been disclosed by



                                                                                  49
                                                                              Chapter 3


this method. All subjects included in this study were medical students who

presumably had better knowledge about the importance of lens hygiene ⎯ this

again may have contributed to the low contamination rate obtained in this study.

Four potential microbial keratitis pathogens isolated from this study included

Xanthomonas maltophilia, P. cepacia, S. liquefaciens and S. plymuthica.



For the study carried by Velasco and Bermudez (1996), they found 81% of

contaminated lens cases. This high contamination rate may again due to the failure

of subjects to follow lens care instructions and poor personal hygiene (see Section

3.2). Common contaminants isolated in this study included S. aureus, S.

epidermidis, Streptococcus viridans, P. aeruginosa and Klebsiella pneumoniae.



3.2.1 Factors contributing to the contamination of lens cases

Contact lens wearers are usually more aware of the hygiene of their contact lenses,

and have better compliance on the care of their contact lenses than for their lens

cases (Collins and Carney, 1986; Gower et al., 1994). There were reports showing

that some contact lens wearers did not discharge disinfecting solutions and air dry

their lens cases after lens disinfection, or rinse their lens cases regularly (Turner et

al., 1993b; Gower et al., 1994). These noncompliance practices allowed lens cases

to become a humid, static, low nutrient environment which were favourable for the

formation of biofilm (McLaughlin-Borlace et al., 1998), and this explain why lens

cases are usually more frequently and heavily contaminated than contact lenses.

Biofilm were less likely to build up on contact lens surfaces then lens case, as

microorganisms adhering onto contact lenses could be removed during lens wear

(Hart and Shin, 1987; Mowrey-McKee et al., 1992).



                                                                                     50
                                                                           Chapter 3


Washing the lens cases with tap water and the keeping case wet did not only

enhance the formation of biofilm, but also allowed the contamination of lens case

by acanthamoeba, as tap water is one of the proven sources of acanthamoeba

(Ledee et al., 1996). In the study by Seal et al. (1999), they studied the effect on

preventing lens case contamination by monthly changes of lenses and lens cases

together with the avoidance of cases coming into contact with tap water. They

reported that the above procedures could help to prevent contamination of lens

cases. A lower bacterial count without the presence of acanthamoeba was found

from patient-used lens cases under these conditions.

Studies have demonstrated the drying up of biofilms for 10 hours or addition of

fresh disinfecting solution can only help to reduce biofilms, but could not totally

eliminate all microorganisms associated within the biofilm (Wilson et al., 1990

and 1991). Regular scrubbing of the interior surface of lens cases, exposing of lens

cases to hot water, air drying of lens cases between use, using two-step hydrogen

peroxide system and regularly replacing lens cases were recommended for

preventing contamination of lens cases (Wilson et al., 1990; Devonshire et al.,

1993; Gray et al., 1995).



3.2.2 Summary

The results of previous studies indicated that the lens case was the most frequently

contaminated item, and lens cases were associated with a wider range of

microorganisms compared to contact lenses. Lens cases were more likely to

support co-contaminations, and mixed bacterial flora has been found in around one

third of contaminated lens cases. High contamination of lens case was likely to be

due to the formation of biofilm inside case chambers, as lens cases were less likely



                                                                                 51
                                                                            Chapter 3


to be clean and disinfected by contact lens wearers. Acanthamoeba which were

seldom present on contact lenses were also isolated from lens cases as contact lens

wearers may not have been aware that they should not allow their lens cases to be

in contact with tap water.



3.3 Contamination of lens care solutions

The contamination rate of lens care solutions recorded ranged from 13% to 63%

(Donzis et al., 1987; Lipener et al., 1995; Velasco and Bermudez, 1996). Lens care

solutions were less likely to be contaminated compared with contact lenses and

lens cases.

In the study of Donzis et al. (1987), lens care solution samples were collected from

the solution bottles of 100 subjects (38 rigid lens wearers and 62 soft lens wearers)

and they reported 13% of contaminated lens care solutions. Nearly all

contaminated lens care solutions, except for one bottle, were still within their

expiration dates. If only solutions used by soft contact lens wearers were

considered, the contamination rate further increased to 26%. This indicated that

lens care solutions used by soft lens wearers were more likely to be contaminated

when compared to those used by rigid lens wearers. They also reported the mean

solution age of the contaminated solutions (13.3 ± 11.6 weeks) was significantly

longer than those solutions without contamination (6.4 ± 6.8 weeks). The most

common contaminants of lens care solutions found in this study included S.

marcescens and Pseudomonas spp., where as acanthamoeba was isolated from

two bottles of home made saline prepared with tap and distilled water.




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                                                                            Chapter 3


In the study by Lipener et al. (1995), the tips of solution bottle rather than the

content was cultured. Bottle tips were cultured by direct immersion onto culture

medium. As mentioned previously, details on how cultures were performed in this

study was not given, it is uncertain if the culture method differed from other

studies. They reported 60% (9 out of 15) of the tested bottle tips were

contaminated. Over half of the contaminated saline bottles were associated with P.

aeruginosa (56%), the others contaminated solutions were contaminated by

Pseudomonas spp. and S. aureus.

Sweeney et al. (1999) investigated contamination rate of lens care solutions used

by contact lens wearers and the effect of solution age on contamination rate. They

dispensed new bottles of preserved saline to each subject, and subjects were asked

to return the bottles of saline for microbial examination at an interval of one week,

two weeks, three weeks, and four weeks. At the end of the study, 298 bottles of

saline were collected and 55% of nozzles and 26% of contents of these solutions

were contaminated. The results indicated that microorganisms were more likely to

be associated with the tips of the solution bottles when compared with the contents.

Contrary to the report by Donzis et al. (1987), Sweeney et al. (1999) did not find

the contamination rate of lens care solutions increased with solution age. This may

be because 28 days were not long enough to show the effect of solution age. In the

study of Sweeney et al., CNS, Bacillus spp., and Corynebacteria spp. were gram

positive bacteria isolated from lens care solutions; whereas P. aeruginosa was the

most common gram-negative bacteria isolated. Sweeney et al. suggested CNS may

probably gain access to the bottles via contact of the nozzle with hands.




                                                                                  53
                                                                             Chapter 3




3.3.1 Summary

The reported contamination rates of lens care solutions ranged from 13% to 63%

(Donzis et al., 1987; Lipener et al., 1995; Velasco and Bermudez, 1996; Sweeney

et al., 1999). Lens care solutions used by soft contact lens wearers and opened for

longer period of time are more likely to be contaminated. The tips of solution

bottles were more likely to be contaminated when compared with the contents.

Serratia spp., P. aeruginosa, S. aureus are common bacteria associated with lens

care solutions, and acanthamoeba were only associated with home-made saline.



3.4 Effectiveness of contact lens care solution against
       microbial contamination

The effectiveness of different disinfecting systems to prevent contamination of

contact lenses and lens cases was another question under debate. In some studies,

hydrogen peroxide systems have been found to be more effective for the

disinfection of contact lenses (Wilson et al., 1990; Wilson et al., 1991; Hiti et al.,

2002). However there were studies showing biofilm present equally frequently

with the use of hydrogen peroxide and chlorine releasing care systems

(McLaughin-Borlace et al., 1998). There were also some studies showing

chemical disinfecting systems were more powerful in preventing the

contamination of contact lenses and lens care accessories (Seal et al., 1999;

Houang et al., 2001; Kilvington and Anger, 2001).




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                                                                           Chapter 3



3.4.1 Hydrogen peroxide system versus chemical disinfecting

       system

In the study by Wilson et al. (1991), 3% hydrogen peroxide disinfecting solution

neutralized with sodium stannate and chemical disinfecting systems formulated

with 0.005% chlorhexidine gluconate, 0.001% polyquaternuim-1 and 0.00005%

polyaminoproyl biguanide as disinfectants were challenged using laboratory

prepared biofilm. They reported a higher reduction in biofilm bacteria and less

incidence of recovery was found after disinfected by hydrogen peroxide systems

when compared with chemical disinfecting systems. However, different results

were reported by Rosenthal et al. (1995). Rosenthal et al. compared antimicrobial

activities of three 3% hydrogen peroxide and five chemical disinfecting solutions.

They inoculated 0.1mL of bacterial suspension (108 CFU/mL) into 10 mL of each

disinfecting solutions. Bacteria used for testing included S. epidermidis, P.

aeruginosa, S. marcescens, C. albicans and A. fumigatus. The number of

microorganisms surviving after the disinfecting time as indicated by the

manufacturers were examined. No statistically significant difference in the

disinfecting power were found between hydrogen peroxide system and chemical

disinfecting system, except for C. albicans. Rosenthal et al. reported that although

hydrogen peroxide was found to be more effective in killing C. albicans, the

number of bacteria and yeast in neutralized hydrogen peroxide increased to over

107 CFU/ml after neutralization was completed.

Seal et al. (1999) compared the antimicrobial activities between hydrogen

peroxide and chemical disinfecting system with a different approach. They

prescribed   either    chemical    disinfecting   solution    containing    1μg/ml

polyhexamethylene biguanide or one of the two one-step hydrogen peroxide


                                                                                 55
                                                                           Chapter 3


system (Oxysept or EasySept) to 150 contact lens wearers. Contact lens wearers

were asked to return their lenses and lens cases for microbial examination after

using for 1 month. A statistically significantly higher contamination rate of lens

cases was found with the use of hydrogen peroxide when compared with those

using chemical disinfecting system. The results of this study may have been

affected by the compliance of the contact lens wearers and their personal hygiene.

Seal et al. (1999) suggested that the high contamination rate observed with the use

of hydrogen peroxide system may be because hydrogen peroxide system did not

include the use of separate detergent-based cleaning solutions for the cleaning of

contact lenses.



In the study by Miller et al., (2001), the disinfecting ability of four chemical

disinfecting solutions (ReNu MultiPlus, Opti-Free Express, Complete Comfort

Plus and Solo-Care) and one hydrogen peroxide system (AOSEPT) were

challenged with bacteria (included human corneal isolated P. aeruginosa) and

fungi. Out of the four chemical disinfecting solutions, two of them only met the

minimum disinfecting criteria for bacteria and did not meet the minimum

disinfecting criteria for yeast or mold. The results of this study demonstrated that

there were variations between disinfection effectiveness among chemical

disinfecting systems. The results of this study also showed that the variation

between results obtained from different studies may because of the use of different

chemical disinfecting systems or hydrogen peroxide systems for the experiment.

Hiti et al. (2002), challenged a chemical disinfecting solution, formulated with

0.0005% polyhexamethylene biguanide, one-step and two-step hydrogen peroxide

systems (with 3% and 0.6% hydrogen peroxide respectively) with the trophozoites



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                                                                          Chapter 3


and cysts of different species of acanthamoeba including: A. castellanii, A.

hatchetti and A. lenticulata. They reported that the two-step hydrogen peroxide

system had the highest amoebicidal effects, followed by one-step hydrogen

peroxide system. The cysts of viable amoeba still viable after the exposure to

chemical disinfecting solution for eight hours.

In contrast to the results of Kilvington and Anger (2001), Hiti et al. (2002),

reported that a chemical disinfecting solution was more effective in killing

amoebal cysts than hydrogen peroxide systems. They compared the effectiveness

of   a   chemical   disinfecting   solution   (Opti-Free-Express   with   0.001%

polyquaternium-1 as disinfectant) and two hydrogen peroxide systems (Oxysept 1

Step and Oxysept 1) in the killing of the cysts of A. polyphaga. Kilvington and

Anger (2001) reported that chemical disinfecting solution was more effective in

the killing of amoebal cysts. The differences between results were suggested to be

caused by the use of different chemical disinfecting solutions and the use of

different species of acanthamoeba. Studies reported that the efficacy of contact

lens disinfecting solutions against acanthamoeba could be influenced by the age

and strains of acanthamoeba cysts used for testing (Niszl, 1998; Kilvington and

Anger, 2001).



3.4.2 One-step versus two-step hydrogen peroxide system

Among the two types of hydrogen peroxide systems (one-step and two-step),

two-step system were preferred and recommended by most investigators (Gary et

al., 1995; Niszl and Markus, 1998; Houang et al., 2001; Huges and Kilvington,

2001; Hiti et al., 2002). Two-step hydrogen peroxide systems allowed a longer

exposure time and was found to have stronger disinfecting power (Niszl and



                                                                                57
                                                                           Chapter 3


Markus, 1998; Huges and Kilvington, 2001; Hiti et al. 2002). One-step systems

offered convenient disinfecting procedure by a single disinfection-neutralization

process, however they were less effective in against contaminants as neutralization

process occurs too rapidly to allow complete disinfection (Wilson et al., 1990;

Huges and Kilvington, 2001). There were studies showed that microorganisms

were able to survive on the platinum (neutralizing) disk of the one-step hydrogen

peroxide   system (Wilson      et   al.,   1990).   Investigators   suggested   that

microorganisms were able to survive on platinum disk because hydrogen peroxide

decomposed immediately after being in contact with the disc (Wilson et al., 1990).

Therefore microorganisms which possess enzyme catalase were also more

resistant to hydrogen peroxide system (Gary et al., 1995).

Since there is no standard protocol for testing anti-acanthamoeba activities of

different disinfecting systems, it is difficult to compare which systems are better

than others.



3.4.3 Summary

Both hydrogen peroxide systems and chemical disinfecting systems have their

own advantages. Hydrogen peroxide systems seem to have better antimicrobial

efficacy, however once neutralization is completed, there was no residual

disinfectant available for continued antimicrobial protection. Chemical

disinfecting systems seem to have less antimicrobial activity, and there are large

variations among different chemical disinfecting solutions, however provide a

prolonged effect during storage contact lenses. In the real situation, both

disinfection and storage of contact lenses are equally important in the prevention




                                                                                 58
                                                                  Chapter 3


of microbial keratitis, therefore practitioners should choose the suitable

disinfecting system according to the need of their patients.




                                                                        59
                                                                          Chapter 4




Chapter 4

Contact lens care compliance

4.1 Studies of lens care compliance

Non-compliance is a well known cause of medical treatment failure, which also

affects the success of contact lens wear. Compliance was defined as “the extent to

which a patient’s behaviour coincides with the clinical prescription.” (Ashburn et

al., 1980). It has been reported that there are strong correlation between

non-compliance with lens care instructions and the presence of signs and

symptoms during lens wear (Collins and Carney, 1986). Non-compliance can lead

to a series of undesirable consequences including: reduction of treatment efficacy,

inducing secondary problems, incorrect prescription and waste of time and money

(Efron. 1997). Improper use of contact lenses and lens care solutions can lead to

serious ocular complications, such as infectious keratitis, which can result in

vision loss (Lee and Lim, 2003). Previous studies have shown that level of

non-compliance among contact lens wearers were high. Around 40%-91% of

contact lens wearers have been reported non-compliant with the use and care of

contact lenses (Collins and Carney, 1986; Chun and Weissman, 1987; Sokol et al.

1990; Turner et al., 1993a & 1993b; Gower et al., 1994; Ky et al., 1998). In order

to know how contact lens wear is affected by non-compliant practices among

contact lens wearers, researchers have carried out studies to assess the level of

compliance among contact lens wearers.




                                                                                60
                                                                            Chapter 4



4.1.1 Study design

Review of the literature, interviews, questionnaire, survey and observation of

subject’s demonstration were common methods used for assessing the level of

compliance among contact lens wearers. Different results were found between

studies.



Collins and Carney (1986) studied the compliance of 100 subjects, recruited from

three different centres. Compliance was assessed through interviews and

observation of subjects’ demonstrations of their lens care procedures. Subjects

were first interviewed on their contact lens habits, and then they were instructed to

perform their normal lens care procedures. The levels of compliance were

evaluated based on the answers given in the interview, and their performance

during the demonstrations. Collins and Carney found 74% of subjects were

non-compliant in at least one lens care procedure, and a total of 14 non-compliant

behaviours were identified (Section 3.2). A significant correlation was found

between the level of subject’s compliance and the presence of signs and symptoms

(including surface deposits, corneal staining and subjective symptoms). Collins

and Carney concluded that non-compliant behaviour can be total or occasional,

and can be reflected in the presence of lens-wearing problems.

Including both interview and observation through demonstration increased the

sensitivity of picking up non-compliant behaviours. Although subjects may not do

what they normally did at home during the demonstration, observation through

demonstration provides another chance for investigators to pick up mistakes that

may not have been realized by the subject. Since contact lens wearers tend to hide




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                                                                             Chapter 4


their non-compliant behaviours from practitioners, the observations should be

made without the lens wearers being aware of the assessment.

In the study by Chun and Weissman (1987), 50 contact lens wearers were studied

through interviews. Subjects were identified as non-compliant wearers if they

were not using the lens care systems prescribed by their practitioners correctly or if

they had poor hygiene. They found that 40% of the subjects were non-compliant

with their prescribed lens care systems. Chun and Weissman identified that contact

lens wearers in the age groups of between 10 to 30 years (47% subjects were

non-compliant) and greater than 50 years (40% subjects were non-compliant) were

more likely to be non-compliant. Moreover lens wearers with more than 2 years of

lens wearing experience (62% subjects were non-compliant) were also less

compliant when compared with new lens wearers (28% subjects were

non-compliant).

The percentage of non-compliance reported by Chun and Weissman (1987) was

much lower than that reported by Collins and Carney (1986). The difference may

be due to the difference in subject selection between studies. Chun and Weissman

recruited 50 subjects from one center only, and this subject group consisted of a

disproportional number of aphakic (16%), hyperopic (6%) and myopic (78%)

subjects, who were using contact lenses with different reasons and in different

modalities. Furthermore, the subject group of Chun and Weissman consisted of

contact lens wearers from a wide age range (8-80) years. As Chun and Weissman

had pointed out, the age of subjects may affect the level of compliance.



In the study by Sokol et al. (1990), the level of compliance was assessed through

telephone interviews. During the interview, the subject was asked to answer 10 pre



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                                                                          Chapter 4


set-questions based on published lens care guidelines. Questions were answered

only with Yes/No. Subjects were identified as non-compliant if they failed to

comply three or more of these guidelines. According to this criterion 46% (23) of

subjects were recognised as non-compliance with lens care procedures. The

percentage of non-compliant contact lens wearers found in this study (46%) is

lower than the 74% that reported by Collins and Carney (1986). The differences in

the results obtained in the two studies were mainly due to different definition of

non-compliant were used in these studies. Collins and Carney reported the

percentage of subjects who fail to comply in one single procedure, where as Sokol

et al. reported the percentage of subjects who failed in three or more procedures.

Sokol et al. (1990) defined noncompliant as such because that allowed their

subjects to be best divided in two relatively equal subgroups. The percentage of

non-compliant contact lens wearers increased to 94% if Sokol et al, (1990) used

the same criterion as Collins and Carney (1986).



According to the definition of compliance, the subject’s behaviour should be

compared with clinical recommendations given by their contact lens practitioners.

However since most subjects in previous studies were experienced, existing

contact lens wearers, it was difficult to collect data on the recommendations given

by their practitioners. Therefore in most previous studies, investigators compared

subject’s lens care behaviours with lens care procedures as recommended by

manufacturers. Coopersmith and Weinstock (1997) studied the level of

compliance of contact lens wearers by comparing their lens replacement schedules

with the recommendations by their contact lens practitioners. Data of

practitioner’s recommendations and subject’s actual replacement of contact lenses



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                                                                            Chapter 4


were collected in two separated surveys. Coopersmith and Weinstock found that

subjects using disposable contact lenses tend to replace their lenses at intervals

longer than the recommended intervals. A around 31% of disposable lens wearers

who were recommended to change their lenses every two weeks actually replaced

their lenses after more than two weeks. About 21% of lens wearers who were

recommended to replace their lenses every six month did not do so.



4.2 Non-compliant behaviours identified

In the studies on the level of compliance, a wide spectrum of non-compliant

behaviours had been identified. These behaviours included improper hand

cleaning, daily cleaning and disinfection of contact lenses, contact lens accessories

care, enzymatic cleaning, attending aftercare and regular lens replacement.




                                                                                  64
                                                                                  Chapter 4


Table 4.2.1 Summary of non-compliance behaviours found among contact lens
wearers on hand cleaning, lens cleaning and lens disinfection.


Hand cleaning                                           % of
                                                   non-compliant
                                                      subjects
Do not always/never wash hand thoroughly before       12-44%     Collins and Carney, 1986
handling contact lenses                                          Sokol et al., 1990
                                                                 Turner et al., 1993a
                                                                 Turner et al., 1993b
                                                                 Gower et al., 1994
                                                                 Claydon et al., 1997
Daily cleaning
Do not always/never use daily cleaner                   20%      Collins and Carney, 1986
Inadequate lens cleaning technique                      29%      Collins and Carney, 1986
                                                                 Claydon et al., 1997
Do not always/never use rinsing solution             5%-15%      Collins and Carney, 1986
                                                                 Turner et al., 1993a
                                                                 Turner et al., 1993b
                                                                 Gower et al., 1994
                                                                 Claydon et al., 1997
Inadequate rinsing technique                            20%      Collins and Carney, 1986
                                                                 Claydon et al., 1997
Do not always/never clean their lenses after         21%-34% Collins and Carney, 1986
removal/before disinfection                                      Turner et al., 1993a
                                                                 Turner et al., 1993b
                                                                 Gower et al., 1994
                                                                 Claydon et al., 1997
                                                                 Ky et al., 1998
Lens disinfection
Shifting of lens care regimen                        12%-16% Chun and Weissman,1987;
                                                                 Sokol et al., 1990
Re-use rinsing/soaking solution                          2%      Collins and Carney, 1986
                                                                 Claydon et al., 1997
Disinfect lenses with inadequate time                   16%      Turner et al., 1993b
                                                                 Gower et al., 1994
Disinfect lenses with inadequate solution               19%      Gower et al., 1994
Do not re-disinfect lenses after they have been         52%      Turner et al., 1993a
stored in case longer than indicated                             Gower et al., 1994
Accessories care
Do not always discard used solution                  5%-13%      Turner et al., 1993a
                                                                 Turner et al., 1993b
Do not always rinse lens case                        36%-47% Turner et al., 1993b
                                                                 Gower et al., 1994
                                                                 Claydon et al., 1997
Do not always air dry lens case                       36-57%     Turner et al., 1993b
                                                                 Gower et al., 1994
                                                                 Claydon et al., 1997
Do not clean contact lens case regularly                28%      Collins and Carney, 1986
                                                                 Claydon et al., 1997
Irregular replacement of disinfecting solution/use   1%-18%      Collins and Carney, 1986
solution beyond expiration date                                  Gower et al., 1994




                                                                                            65
                                                                                  Chapter 4


Table 4.2.2 Summary of non-compliance behaviours found among contact lens
wearers on enzymatic cleaning, regular aftercare and lens replacement.

Enzymatic cleaning
Carry enzymatic cleaning less than once a week             43%-71% Sokol et al., 1990
                                                                   Ky et al., 1998
Add lenses to vial before tablet is dissolved             43%      Turner et al., 1993b
Do not shake enzyme vial                                  40%      Turner et al., 1993b
Soak lenses in enzyme longer than indicated               43%      Turner et al., 1993b
Do not always rinse lenses after enzymatic cleaning       4%       Turner et al., 1993b
Do not always disinfect lenses after enzymatic cleaning   41%      Turner et al., 1993b
Regular aftercare and lens replacement
Do not have regular schedule for lens checked             56%        Sokol et al., 1990
Do not replace lenses regularly                           56%        Sokol et al., 1990
                                                                     Coopersmith and
                                                                     Weinstock, 1997



A summary of common non-compliant behaviours identified by previous

investigators is shown in Table 4.2.1 and Table 4.2.2. The results of previous

studies showed that most contact lens wearers showed a certain degree of

non-compliance with their care procedures. A range of 12%-44% of contact lens

wearers had been reported to fail to always wash their hands before handling their

contact lenses (Collins and Carney, 1986; Sokol et al., 1990; Turner et al., 1993a;

Turner et al., 1993b; Gower et al., 1994; Claydon et al., 1997); and 12%-16% of

contact lens wearers did not use lens disinfecting regimens that were prescribed by

their practitioners (Chun and Weissman, 1987; Sokol et al., 1990). It is a concern

to find that a significant (44%) of contact lens wearers ignored hand hygiene

before handling their contact lenses. Hand washing is the first step of lens care,

and it is not hard to understand the important of hand hygiene, yet up to 44% of

contact lens wearers had been reported to be non-compliant with this initial step of

lens handling.

A total of 29% and 20% of contact lens wearers were found to have inadequate

techniques in cleaning and rinsing their contact lenses respectively (Collins and

Carney, 1986). This indicated that in some cases, even contact lens wearers



                                                                                          66
                                                                            Chapter 4


wanted to be compliant with certain lens care procedures, they may not have

adequate techniques to carry it correctly.

In addition to wearing contact lenses longer than recommended and not replacing

lenses regularly (Sokol et al., 1990; Claydon et al., 1997; Coopersmith and

Weinstock, 1997) as mentioned in Section 3.1.2, there were other non-compliant

behaviours with the use of contact lenses. There were contact lens wearers who did

not check lenses before insertion (Claydon et al., 1997). Sokol et al., (1990) found

that over half of the contact lenses wearers (56%) in their study had the experience

of swimming or bathing with their lenses on the eyes. They also reported there

were around a quarter of the contact lens wearers (26%) who did not always

remove their lenses when their eyes go red or irritated. This showed that a

proportion of contact lens wearers did not know or were not concerned about when

they should not wear their contact lenses and the importance of removing their

lenses when there were symptoms of any abnormalities.



There were also some inappropriate usages of lens care solutions identified by

previous investigators. In the studies out carried out by Turner et al. (1993a & b)

and Claydon et al. (1997), a small percentage of the contact lens wearers used tap

water to rinse their lenses. They also reported contact lens wearers who did not use

fresh solution to store their lenses and there were also contact lens wearers use tap

water or even saliva with their contact lenses. Turner et al. (1993b) reported

contact lens wearers using tap water to dissolve enzyme during enzyme cleaning.

Ky et al. (1998) reported a small percentage (5%) of contact lens wearers using

saline as their only lens care solution - simply because they did not know the

difference between the function of saline and disinfecting solutions. There were



                                                                                  67
                                                                            Chapter 4


also a small percentage of contact lens wearers who had the experience of putting

their contact lenses in their mouth and use their saliva to clean them (Sokol et al.,

1990; Claydon et al., 1997). Although these non-compliant behaviours were rare

and only involved a small percentage of contact lens wearers, attention should still

be given to possible non-compliant behaviours as wearing contact lenses that are

not disinfected properly, by appropriate disinfection with suitable solutions, can

increase chance of developing contact lens-associated microbial keratitis.



To conclude, nearly all contact lens wearers are non-compliant on the use of

contact lenses to a certain degree. Contact lens wearers could be non-compliant in

every single step of lens care procedures. Practitioners should never assume

contact lens wearers to be compliant even if they were well educated and

experienced contact lens wearers. Non-compliant behaviours was hard to detect as

it can be total or occasional (Collins and Carney 1986). In some cases, contact lens

wearers did not comply because they did not realize that they were making

mistakes or because they did not have adequate knowledge or technique to take

care of their contact lenses correctly.



4.3      Clinic significations of non-compliant behaviours

Beside the level of compliance, Turner et al., (1993a & 1993b) also wanted to

know how these non-compliant behaviours were affecting contact lens wear in

term of safety and comfort. In their study, the subject’s compliance was first

evaluated by an interview, based on their answers given each subject was given a

score for each assessed items. This individual subject score for each item was

adjusted by mean important weighting factors of safety and comfort, and became



                                                                                  68
                                                                           Chapter 4


weighted item individual scores of safety and comfort respectively. Mean

important weighting factors were obtained by asking a panel consisting

optometrists and ophthalmologists to grade each lens care procedure (with 0 being

the least important and 9 being the most important) according to its importance of

safety and comfort. The mean important weighting factors were then calculated by

taking the mean of grades given by practitioners. Weighted item individual scores

of safety and comfort were obtained by multiplying individual subject score for

each item with the mean important weighting factors of safety and comfort

respectively. Any score larger than or equal to six were indicating significant risk

(having safety problems or lens wearing discomfort) associated with lens wear.



Turner et al. (1993a) found that 99% of their subjects using AOSEPT were

non-compliant with at least one procedure and 84% non-complied with lens care

procedures that were affecting the safety of lens wear. In another study carried out

by Turner et al. (1993b), they reported that 91% of their subjects using ReNu were

non-compliant with lens care procedures. In the study of Gower et al. (1994), they

reported that subjects who used AOSEPT (84%) and ReNu (91%) disinfecting

systems were more likely to be noncompliant with procedures identified as

associated with lens wearing safety than those using OPTI-FREE (55%).



Gower et al. (1994) concluded that the level of compliance on lens care procedures

associated with lens wearing comfort were similar, among contact lens wearers

using these three lens disinfecting regimens. Generally, around one-third of

subjects (34%-37%) using each lens disinfecting regimens were non-compliant to

at least one lens care procedure that affected lens wearing comfort. They suggested



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                                                                           Chapter 4


that contact lens wearers were more motivated to change their behaviour when it

was associated with discomfort of lens wear. On the other hand, it was harder for

subjects to change their noncompliant behaviour if the behaviour only affected the

safety of lens wear.

Gower et al. (1994) also found the use of MPS, simplified daily cleaning

procedures by eliminated the use of daily cleaner, does not help to increase

compliance in lens cleaning of the subjects using ReNu or OPTI-FREE. Subjects

using OPTI-FREE were associated with less significant risk (in lens wearing

safety) than those using AOSEPT and ReNu due to the differences between

formulations of these lens disinfecting solutions. OPTI-FREE simply reduced the

numbers of procedures that patient were required to do. For example, the use of

OPTI-FREE does not require contact lens wearers to redisinfect their contact

lenses after soaking lenses in the lens case for more than one day as is required in

AOSEPT system and after enzyme cleaning as with ReNu.



4.4        Reasons of non-compliance in contact lens wear

Another question is that ‘Why contact lens wearers were being non-compliance

with their use of contact lens and lens handling?’ In order to understand the reason

of non-compliant behaviours among contact lens wearers, Sokol et al. (1990)

investigated this issue with a health belief model. They aimed to find out whether

there are any differences between health beliefs of compliant and non-compliant

contact lens wearers. Subjects were first divided into the compliance and

non-compliance group according to their score of a questionnaire about their lens

caring habits. Subjects who failed to comply with three or more lens care

procedures were recognized as non-compliant lens wearers. Sokol et al. found that



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                                                                             Chapter 4


46% of subjects were non-compliant with proper lens care procedures, and contact

lens wearers under age 30 and those wearing contact lens for cosmetic and

convenience reasons were more likely to be more non-compliant.

After dividing the subjects into groups, the health belief model was used to assess

subjects’ health beliefs. The health belief model explored subjects’ attitudes in

four different areas: (1) Susceptibility - this referred to a question on whether the

subject was susceptible to this problem; (2) Severity - this referred to a question

how severe the subject expected the problem could be; (3) Benefits – this referred

to subjects’ impression on whether this problem could be prevented; (4) Barriers –

this referred to the barriers which the subject needed to overcome in order to

prevent the problem. This model helps to identify the most important underlying

perception of subjects’ non-compliant behaviours.

No significant differences were found in all 12 belief statements between the

compliant group and the non-compliant group. There were 7 statements found to

be positively correlated with non-compliant behaviours but without statistical

significance. Sokol et al. pointed out that the lack of significant differences

between groups may be because of the inclusion of atypical subjects. Since a

number of students, highly educated lens wearers and professionals in other

health-related fields were included in this study. Although no statistical significant

result was obtained with the health belief model, Sokol et al. still found it an

effective model to use for the investigation of non-compliant behaviour. They

believed that a significant result could be obtained with large samples.

Unfortunately, no such study has been conducted so far.




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                                                                           Chapter 4


Beside the level of compliance, Ky et al., (1998) also studied how well contact lens

wearers knew about the proper use of contact lenses. They wanted to know

‘whether low level of compliance is resulted by contact lens wearers are not

compliance or it is because they do not know how to take care and use their contact

lenses correctly?’ Subjects were asked to complete a questionnaire which

consisted of six true/false questions, and their knowledge on the use of contact

lenses was assessed based on their answers. The mean number of correct responses

to the six questions was 3.74. Ky et al., (1998) found there were contact lens

wearers who bought their contact lenses through eyeglass stores, mail order

companies or lens warehouses. They also found that 8% of lens wearers used

saline as the primary modality of disinfection and 24% of subjects believed that

saline could be used for contact lens disinfection and storage. Over half of the

subjects (56% and 64%) did not know that it is improper to wear contact lenses

while in Jacuzzis or swimming. They concluded that their results reflected that

quite a lot of contact lens wearers did not have adequate knowledge on the use of

contact lenses, as up to 64% of the contact lens wearers obtained incorrect answer.

They found that contact lens wearers were not familiar with the proper care and

use of contact lenses. They concluded that adequate knowledge on proper lens care

is one of reasons of the low level of compliance.



4.5 Enhancement education on compliance

If non-compliance is a result of inadequate knowledge on lens care, then ‘Can

compliance be improved by any kind of enhancement education?’ Claydon et al.

(1997) carried out a prospective, randomized, controlled and double masked study

to assess the effect of an enhancement strategy (Video, booklets, posters, a



                                                                                 72
                                                                            Chapter 4


checklist and a health care contract) on the level of compliance. It is a 12-month

research including 80 asymptomatic and experienced contact lens wearers.

Subjects were randomly divided into two groups, Groups 1 & 2. All subjects in

both groups received a basic level of education including an explanation and

demonstration on the use of ReNu solution. Subjects in Group 2 received

additional enhancement materials on lens care which included a video, booklets,

posters, a checklist, reminders and a health care contract.

At the end of the study, the levels of compliance of all subjects were assessed and

compliance was defined based on six instructions of the use of ReNu published by

the manufacturers and three additional criteria: never use tap water or saliva to

wet/clean contact lenses, removed lenses and contacted practitioner if there were

any ocular problems and attended all aftercare visits. Lens cases of subjects were

also collected and cultured for the presence of bacteria, fungi, yeast and protozoan,

Acanthamoeba.

Seventy-two subjects completed the study. Statistical tests showed no differences

between the compliance scores of Group 1 and Group 2 at the 12-month aftercare

appointment. No statistically significant difference were found between Group 1

and Group 2 with respect to ocular response, appointment keeping compliance,

number of contact lenses used by subjects and the number of bottles of ReNu used

by subjects. No statistical significant different were found between contamination

found in Group 1 and Group 2. A total 63 contact lens cases were collected for

microbiological assessment and 30% of these lens cases were found to be

contaminated with microorganisms. Claydon et al. concluded that compliance

enhancement strategy had no effect on lens case hygiene. They suggested that the

lack of significant difference on the improvement of compliance between the two



                                                                                  73
                                                                          Chapter 4


groups of subjects may be due to generally high levels of compliance among the

subjects. The level of compliance was high in this study because they had included

a large proportion of well-educated subjects in this study. Moreover they supplied

free lens disinfecting solutions to subjects; this action may enhance the

compliance in appointment keeping among contact lens wearers. Other possible

reasons may be because the sensitivity of the compliance assessment used in this

study was not high enough to detect small differences on the level of compliance

between groups, especially when the subjects were generally compliance and they

were all using MPS.



4.6 Summary

Compliance is a complex subject hard to study as it could be influenced by a wide

spectrum of factors such as subject background, experimental design and

definition of compliance. Non-compliance with contact lens care is commonly

found among contact lens wearers, and the spectrum of non-compliance lens care

procedures is wide. A large proportion of contact lens wearers are non-compliance

with lens care procedures that are associated with significant risks ocular

complications, and around one third of contact lens wearers were non-compliant

with procedures associated with lens wearing comfort. Simplicity in lens

disinfecting procedures alone does not help to improve the compliance of lens

wearers. Contact lens wearers were more willing to change their lens care habits

that affected their lens wearing comfort. A correlation was found between the level

of compliance and the presence of ocular sign and symptoms during contact lens

wearers. Contact lens wearers under 30 years of age and are experienced lens

wearers are more likely to be non-compliant. Some contact lens wearers are being



                                                                                74
                                                                        Chapter 4


non-compliance because they do not have adequate knowledge on proper care and

use of contact lenses. The effect of health belief on the level of compliance and

whether compliance could be improved by enhanced education is still unknown.

More research on contact lens compliance are still required to increase our

understanding of the underlying factors in this area and to promote better

compliance among contact lens wearers.




                                                                              75
                                                                          Chapter 5




Chapter 5

Vision Correction with Contact Lenses
in Hong Kong


A number of studies (Goh et al., 1993; Lam et al., 1991) have documented the high

prevalence of myopia in Hong Kong. With the increase in the number of myopes,

there is also an increase in the demand of contact lenses for vision correction.

Together with the introduction of new contact lens designs and materials, the trend

in the fitting of contact lenses has changed rapidly over recent years (see Section

1.1). The presence of contact lens-associated microbial keratitis is highly

associated with the usage of contact lenses. Regular review on the contact lens

usage in Hong Kong is very important. The first survey on contact lens usage in

Hong Kong was conducted in 1990 (Conway et al., 1990), followed by a second

one four years later (Cho et al., 1994), and the latest was conducted by Cheung et

al. (2002).



5.1 Aims

The objectives of the current survey were to identify the current practitioners’

prevalence of contact lens fitting, their opinions on the use of speciality contact

lenses and lens care products, and their opinions on the marketing support and

future trends of contact lens development.




                                                                                76
                                                                           Chapter 5



5.2 Methodology

5.2.1 Investigation techniques

Self-administered questionnaire

Data was collected by a self-administered questionnaire (Appendix I); the

questionnaire (in Chinese) (Appendix II) was distributed to subjects in April 2002

by mail. To encourage return of the questionnaire, a stamped envelope with return

address was attached to each. The questionnaire was re-sent one month after the

(first) deadline to remind practitioners to return the questionnaire if they had not

done so.



Telephone interview

Follow-up telephone interviews were also conducted with 30 practitioners from

randomly-selected practices to collect their comments on specific items and/or to

clarify issues raised in the questionnaire. Optical shops were contacted according

to the order they were listed on the Yellow Page telephone directory (as at 31

March, 2003) and asked whether their practitioners were willing to be interviewed.

After calling 162 optical shops, 30 practitioners agreed to be interviewed.




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                                                                              Chapter 5


Table 5.1 Classification and restriction on the practice of the Optometrist Register
in Hong Kong.


Part of     Qualification/eligibility               Restriction on practice       No. of
Register                                                                        registrants#
            Bachelor degree/Professional            May use diagnostic
I                                                                                  456
            Diploma in Optometry                    pharmaceutical agents

            Higher Certificate in Optometry or      Not allowed to use
            other qualifications together with      diagnostic
II                                                                                 244
            training, professional experience and   pharmaceutical agents
            skill satisfying the Council*           except staining agents

            The applicant has acquired substantial
                                                   To practise refraction
III         knowledge, experience and skill in the                                  78
                                                   only
            practice of his profession

            The applicant has acquired substantial
            knowledge, experience and skill in the Not allowed to use
IV          practice of his profession or passed   diagnostic agents               665
            Optometrists Board examination on      except staining agents
            refraction and contact lens fitting

            The applicant has acquired substantial
            knowledge, experience and skill in the
                                                   To practise refraction
IV          practice of his profession or passed                                   438
                                                   only
            Optometrists Board examination on
            refraction

#As at 1 April 2002
*the Council: the Supplementary Medical Professionals Ordinance




5.2.2 Subject selection criteria

All registered contact lens practitioners, who were allowed to practise contact

lenses in Hong Kong (being registered under the Optometrists Board (Table 5.1),

were included. We excluded registered practitioners residing or practising abroad

and those in full-time academia.




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5.3 Results

As we were targeting annual changes in the contact lens market in Hong Kong,

most of the questions required practitioners to give estimates rather than exact

numbers. In the following paragraphs the results presented were the averages of

the figures provided by the respondents (ranges were also presented to show the

wide range of differences between practitioners).



Table 5.3.1 Numbers of responses from practitioners in each category of
registration.



                        No. of             No. of responses                No. of responses
                     questionnaires         Current study                Cheung et al., 2002
                          sent         (based on 2002 figures)         (based on 2000 figures)

 Part I                  412                    118                              87

 Part II                 230                    42                               58

 Part IV                 664                    126                             130

 Total                  1306                    286                             275




                          Private practice             Optical chain            Clinic/hospital
              100
              90
              80
              70
 Percentage




              60
              50
              40
              30
              20
              10
               0
                    Overall (N=286)   Part I (N=118)     Part II (N=42)     Part IV (N=126)



Figure 5.3.1 Nature of practices that respondents worked in.



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                                                                          Chapter 5



5.3.1 Response rate

A total of 286 questionnaires were returned, representing a return rate of 22%. The

distribution of the return rates from Parts I, II and IV practitioners is shown in

Table 5.3.1. Fifty one per cent of the respondents worked in private practices, 44%

worked in chain optical shops and the remaining worked in clinics or hospitals

(Figure 5.3.1). The numbers of contact lens practitioners in each practice ranged

from one to nine (average two).



                           Non-contact lens wearers       Contact lens wearers
                80
                70

                60
   Percentage




                50

                40
                30
                20

                10

                0
                       Myopic           Hyperopic          Emmetropic



Figure 5.3.2 Distributions of contact lens and non-contact lens wearers consulting
the respondents.




5.3.2                Refractive errors of contact lens wearers

About 36% of patients visiting the practitioners were contact lens wearers (Figure

5.3.2) and among contact lens wearers, 94% were myopes. The ratio between new

fit and refit contact lens wearers was about 1:3. The youngest contact lens patient

of each surveyed practitioner was aged between 10 and 14 years old (58%) and the

oldest patient was mostly between 50 and 59 years old (50%). In telephone


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                                                                                       Chapter 5


             interview, most practitioners (18/30) also reported that their new contact lens

             patients were mainly secondary school students (aged between 11 and 18 years).



             5.3.3          Number of aftercare visits

             The average number of aftercare visits during the first year of contact lens wear

             was reported to be four for rigid lens wearers (both PMMA and RGP lens wearers)

             (range: 1-12), three for soft contact lens wearers (range: 1-12) and 12 for ortho-k

             lens wearers (range: 3-50). In the second year of contact lens wear, the average

             number of aftercare visits required for both rigid and soft lens wearers was two

             (range: 0 - 8) and for ortho-k wearers was six (range: 1- 20).




                                                                 Current study        Cheung et al. (2002)

             70

             60

             50
Percentage




             40

             30

             20

             10

             0
                    Planned        Conventional          RGP             PMMA        Orthokeratology
                  replacement         (Soft)
                      (Soft)




             Figure 5.3.3 Comparisons of the proportions of different types of contact lenses
             prescribed between current findings and those reported by Cheung et al. (2002).




                                                                                             81
                                                                                         Chapter 5




                                                    Current study        Cheung et al. (2002)

             30


             25


             20
Percentage




             15


             10


              5
             #No usage of these lenses was reported by Cheung et al. (2002)
             DW: Daily wear
              0
             EW: Extended wear
                      Daily          Biweekly        Monthly         #Silicone      #Silicone
                   Disposable       Disposable      Disposable      Hydrogel DW    Hydrogel EW



             Figure 5.3.4 Comparisons of the proportions of different planned replacement soft
             contact lenses prescribed in the current study and in the study of Cheung et al.
             (2002).




             5.3.4          Contact lens types

             Most of the prescribed contact lenses were soft lenses (93%). PR lenses (66%)

             were the most popular type of contact lenses prescribed by practitioners (Figure

             5.3.3). Surveyed practitioners reported that the major type of rigid lenses fitted

             was RGP lenses (average 5%); PMMA and ortho-k lenses were both fitted to less

             than 1% of patients. Among PR lenses, daily disposable lenses (25%) were

             reported to be the most commonly prescribed lenses, followed by biweekly (23%)

             and monthly (15%) replacement lenses (Figure 5.3.4). SH lenses were prescribed

             to only 3% of patients (Figure 5.3.4) ⎯ 77% of these lenses were prescribed for

             DW and 23% for EW.




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                                                                          Chapter 5


Telephone interviewed practitioners has different opinion on the usage of RGP

contact lenses. A total 67% (20/30) of interviewed practitioners prescribed RGP

contact lenses, nine agreed that there was a decreased usage of RGP contact lenses,

nine found no change and the remaining two found an increased usage of these

contact lenses. The remaining 33% (10/30) interviewed practitioners did not

prescribe rigid lenses, as they (7/10) found the demand for these lenses too small.

On EW contact lenses, interviewed practitioners expressed concerns of serious

ocular complications associated with overnight wear of contact lenses (9/30). Low

market demands (7/30) and high cost of these lenses (4/30) were other major

reasons for the limited usage of SH in EW basis.




Table 5.3.2 Most commonly recommended wearing schedules (average) for each
type of contact lenses.



                                      Hours per day               Days per week

 PMMA                               10 {range: 5-14}              6 {range: 2-7}

 RGP                                12 {range: 4-18}              6 {range: 5-7}

 Ortho-k                             8 {range: 7-18}              7 {range: 4-7}

 Conventional DW                    12 {range: 8-16}              6 {range: 5-7}

 Conventional EW                    12 {range: 9-18}              6 {range: 5-7}

 Daily Disposable                   12 {range: 9-18}              6 {range: 1-7}

 Biweekly Disposable                12 {range: 9-18}              6 {range: 5-7}

 Monthly Disposable                 12 {range: 9-18}              6 {range: 5-7}

 Silicone hydrogel DW               14 {range: 10-24}             6 {range: 5-7}
DW: Daily wear
EW: Extended wear




                                                                                   83
                                                                           Chapter 5



5.3.5          Commonly recommended wearing schedule

The most commonly recommended wearing schedule for DW RGP, conventional

and most PR soft lenses was 12 hours a day and six days per week (Table 5.3.2),

while that for DW of SH contact lenses was 14 hours (range: 10-24) a day and six

days (range 5-7) per week. For EW, most practitioners (81%) usually prescribed

SH contact lenses for two to 10 days EW and less than one fifth (19%) of the

practitioners prescribed theses lenses for more than 10 days EW.



5.3.6          Use of toric contact lenses

On average, practitioners fitted only around 48% of their astigmatic patients (those

with cylindrical correction greater than –0.75 D) with toric contact lenses. The

majority of respondents agreed that the disposable toric contact lenses currently

available in the market, if appropriately fitted, could provide clear and stable

vision (69%), and that the ranges of spherical power (63%) and axis (54%) were

adequate to cover the needs of their patients. However, 73% and 59% of

respondents disagreed that there were adequate choices of base curve and

cylindrical power, respectively.




                                                                                 84
                                                                                          Chapter 5




             50
             45
             40
             35
Percentage




             30
             25
             20
             15
             10
             5
             0
                   Contact lenses with Monovision contact   Bifocal contact    Multifocal contact
                    over-spectacles         lenses              lenses               lenses



              Figure 5.3.5 Proportions of different management protocols for presbyopic contact
              lens wearers.




                  5.3.7        Management of presbyopic contact lens wearers

              Single vision contact lenses used in conjunction with over-spectacles, and

              monovision contact lenses were the most common recommendations for

              presbyopic patients seeking contact lens wear (Figure 5.3.5). On average, bifocal

              and multifocal contact lenses were prescribed to 8% (range: 0-40%) and 8% (range:

              0-50%), respectively, of their contact lens wearing presbyopic patients. From the

              interview, practitioners reported that the limited usage of bifocal/multifocal lenses

              was due to low market demand (17/30), concern with a possible high rate of

              unsatisfactory visual performance (11/30) and high cost price (4/30) of these

              lenses. For interviewed practitioners, who prescribed bifocal/multifocal lenses

              (19/30), most (13/19) did not find that the introduction of PR bifocal/multifocal

              lenses encouraged them to increase the usage of these lenses. As from experience,



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             they felt that these lenses could not provide better vision (both distance or near)

             compared with conventional bifocal/multifocal lenses.


                   Rubbing with cleaner      Rubbing without cleaner      No rubbing recommended

             30
                         Hydrogen peroxide                        Multipurpose solutions


             25


             20
Percentage




             15


             10


             5


             0
                  AOSept    Oxysept      Titmus    Renu     Opti-Free Complete        Solo      Others
                              B12                 MultiPlus Express                   Care




             Figure 5.3.6 Proportions of recommended disinfecting regimens for contact lens
             wearers.




             5.3.8         Recommended contact lens care regimen and use of
                           daily cleaner

             For soft lenses, the most commonly recommended care regimen was MPS (62%)

             followed by hydrogen peroxide systems (38%) (Figure 5.3.6). In the telephone

             interviews, the majority of practitioners (19/30) agreed that the increased

             popularity of PR contact lenses has also led to an increased usage of MPS. For

             chemical care systems, all survey respondents recommended rubbing of lenses

             during lens cleaning; 64% recommended patients using MPS to rub their lenses

             with separate daily cleaner and 36% to rub with the MPS. For hydrogen peroxide



                                                                                                 86
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systems, 98% of respondents recommended their patients to rub lenses with daily

cleaner; whereas the remaining 2% did not recommend rubbing to their patients.

Most interviewed practitioners (19/30) commented that, from experience, MPS

alone, without rubbing, was inadequate for removing dirt or deposits on contact

lenses. The most commonly recommended multipurpose care system was Bausch

& Lomb ReNu MultiPlus and the most commonly recommended hydrogen

peroxide system was Ciba Vision AOSEPT (Figure 5.3.6).



5.3.9 Recommended enzymatic cleaning schedule

For conventional soft lenses, most respondents (91%) recommended weekly

enzymatic cleaning. About 35% and 44% of the respondents recommended

monthly disposable lens wearers use enzymatic cleaning weekly and biweekly,

respectively. For rigid lenses, most respondents recommended weekly (56%) or

biweekly (32%) enzymatic cleaning to their contact lens wearers.




                                                                            87
                                                                                    Chapter 5




             90
             80
             70
Percentage




             60
             50
             40
             30
             20
             10
             0
                  Dryness      Tearing      Foreign    Blur vision     Pain       Redness
                                             body
                                           sensation


              Figure 5.3.7 Common complaints made by contact lens wearers.




              5.3.10        Common complaints of contact lens wearers

              Most respondents (82%) ranked dryness during contact lens wear as the most

              common complaint made by contact lens wearers (Figure 5.3.7). The majority of

              respondents (64%) recommended eye drops to over 90% of their patients. Of these

              respondents, 69% recommended multi-dose eye drops; the other 31%

              recommended unit-dose artificial tears. Of the multi-dose eye drops the most

              commonly prescribed is Senju Contact Lens Lubricant (Senju Pharmaceutical Co.,

              LTD) (48%); where as Tears Naturale Free (Alcon) is the most commonly

              prescribed unit-dose eye drops (72%).




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                                                                           Chapter 5



5.3.11         Availability and future development of speciality
               contact lenses

In this study ‘speciality contact lenses’ included custom-made toric lenses, bifocal

lenses, multifocal lenses, ortho-k lenses and SH lenses.

Most respondents (91%) prescribed custom-made toric lenses. SH lenses were

fitted by 65% of respondents, whereas multifocal and bifocal contact lenses were

available only in 45% and 51% of practices, respectively. Only 15% of the

surveyed contact lens practitioners prescribed ortho-k lenses.

According to the ranking by the respondents, prescription of SH lenses on a DW

basis was expected to have the highest potential for development in the Hong

Kong contact lens market (27%); followed by custom-made toric, multifocal and

SH lenses prescribed on an EW basis.



5.3.12          Sources of contact lens information

Direct communication with contact lens suppliers was the major channel through

which most respondents (68%) obtained updated contact lens information.

Professional journals (13%), colleagues (7%), advertisements (6%) and

continuous education courses (6%) were the secondary and tertiary sources of new

product information for respondents.



5.3.13          Promote the use of contact lenses

Most of our respondents (40%) found advertising to be the most effective way to

help them to increase contact lens sales, followed by discount offers (25%) and

free trial fitting of lenses (22%).




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                                                                              Chapter 5



5.4 Discussion

With the increased incidence of myopia, as expected, most contact lenses (94%)

were prescribed for myopia correction. From the results, 58% of respondents

reported that their youngest contact lens patients were between the age of 10 and

14 years. It is in agreement with the results obtained from the interviews, most

practitioners reported that new contact lens patients were mainly secondary school

students. Practitioners are now more accepted to prescribe contact lenses to young

patients, hence it is expected that there will be a growing demand for contact

lenses among teenagers and young adults.



The numbers of aftercare visits offered to soft and rigid contact lens wearers have

not changed much compared with earlier studies (Conway and Cho, 1990 and Cho

et al., 1994), remaining at around four for both soft and rigid lenses in the first year

of wear. The number of aftercare visits for ortho-k was much more than for others

lens types. More after care visits are necessary in ortho-k, in view of fitting ortho-k

included a lot of demanding procedures (Fan et al., 1999; Cho et al., 2002). There

was a wide range in the number of aftercare visits (range: 3-50) among

practitioners prescribing ortho-k. This show the varies in fitting relationship

between practitioners, these differences may due to different contact lens

backgrounds (Table 5.3.1) of contact lens practitioners registered in Hong Kong as

they are permitted to prescribed ortho-k lenses without additional training.



The usage of soft contact lenses has further increased to 93% in the current study

from 88% in the last one (Cheung et al., 2002). Replacing conventional soft lenses,

PR contact lenses have become the major lens regimen prescribed in Hong Kong.



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                                                                             Chapter 5


The increased popularity of PR contact lenses is likely to be part of a global trend

(see Section 1.1.2). Among PR contact lenses, the use of daily disposable lenses

has become the most popularly prescribed modality (Figure 4.4). The increased

popularity of daily disposable lenses may be due to their advantages on

eliminating contact lens solution problems, reduce contact lens complications and

allow more convenient contact lens wear (see Section1.1.2). However,

conventional lenses will never be totally replaced as it is the lenses to fall back on

when PR contact lenses failed and for patients with special needs.



The usage of RGP contact lenses appears to have decreased, however this may be

misleading because in the current study a large number of our respondents worked

in optical chain stores (Figure 5.3.1) which usually do not provide RGP contact

lens fitting. At the interviews, no consistent comments on the usage of RGP

contact lenses was obtained from interviewed practitioners; there are reports of an

increase, decrease and no changes on the usage of RGP contact lenses. Interviewed

practitioners commented that RGP contact lenses are prescribed mostly to current

RGP contact lens wearers or to those who are not suitable for soft lens wear. It

seems that it is a world wide trend of low usage of RGP with the increase

popularity of soft contact lenses.



This is the first study reporting the usage of SH contact lenses in Hong Kong. The

usage of these lenses on EW basis is limited by practitioners’ concerns about

serious complications with EW (see Section 1.1.2.1). SH contact lenses were still

found to be associated with contaminants and deposits accumulation (Willcox et

al., 2001; Beattie et al., 2003; Jones, 2003). Therefore most SH contact lenses



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prescribed in Hong Kong, as in Australia (Woods and Morgan, 2002), were only

use for DW but for longer wearing hours. Only a small proportion of SH contact

lenses were prescribed for EW in Hong Kong, and they were mostly recommended

to be worn for less than 10 days rather than 30 days as recommended by

manufacturers.



The usage of ortho-k lenses is also limited due practitioners’ concern that

scientific evidence on the efficacy of myopia control was lacking (see Section

1.1.1.3) and increased risk of infectious complications associated with overnight

lens wear (Chalupa et al., 1987; Cohen et al., 1987; Weissman and Mondino,

20002; Stapleton, 2003). Inadequate training in fitting techniques, inadequately

equipped ortho-k practices and low market demand were other factors limiting the

number of practitioners fitting ortho-k lenses in Hong Kong (Cheung et al., 2002).



From the current survey results, only 48% of the astigmatic contact lens wearers

(cylindrical correction greater than -0.75 D) consulting the surveyed practitioners

were fitted with toric lenses. This low usage of toric lenses may be due in part to

the limited parameters of toric PR contact lenses. Our respondents reported that

the current choices of base curve and cylindrical power available were inadequate

to cover the needs of their astigmatic patients. As the demand for PR contact lenses

increases, there will be a need for manufactures to increase the range of parameters

of these lenses.



The usages of bifocal/multifocal lenses were limited by low market demand,

concern with a possible high rate of unsatisfactory visual performance and high



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                                                                              Chapter 5


cost price of these contact lenses. In the United States, the usage of bifocal lenses

increased with the introduction of PR bifocal lenses (Barr et al. 2000), however, no

such effect was observed in Hong Kong. Our respondents felt that these lenses

could not provide better vision (both distance or near) compared with conventional

bifocal lenses. Until the mindset of practitioners is changed and their confidence in

these lenses is increased, it is unlikely that the use of these contact lenses will

change significantly.



Our results show that, same as previous study, MPS is the most popularly

recommended disinfecting regimen, followed by hydrogen peroxide. Interviewed

practitioners agreed that the popularity of MPS is correlated with the increased

usage of PR contact lenses, as this combination facilitated convenient contact lens

wear. Although ‘no rubbing’ formulas are being promoted by some MPS

manufacturers, all practitioners in this survey recommended their MPS patients

rub their lenses with or without daily cleaners when cleaning their lenses. It is

because they found that MPS alone, without rubbing was inadequate for removing

dirt or protein on lens surfaces.



Over 80% of the respondents ranked dryness during contact lens wear as the most

common complaint made by their patients. This explained why more than 60% of

our respondents prescribed artificial tears to nearly all (over 90%) of their patients.

This indicates that ocular dryness continues to be the most challenging problem

for contact lens wear, and there is a demand for new contact lenses which can

minimise dryness and allow more comfortable lens wear.




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                                                                             Chapter 5


Although continuing education courses are available to practitioners in Hong

Kong, practitioners had found it difficult to attend because of their long working

hours. Therefore contact lens suppliers, who provide direct access and free

information of new products, have become the major source of new contact lens

information for practitioners in Hong Kong. With the advances in technology,

with more and more new types of contact lenses appearing in the market,

appropriate on-going training for practitioners to keep their skill up-to-date to

provide full-scope contact lens practice are necessary. There is a need to design

and organise continuing education courses to suit the practitioners’ needs if these

courses are to be effective.



5.5 Conclusion

In conclusion, the contact lens market in Hong Kong is driven by younger contact

lens wearers. With the increasing demand for convenient contact lens wear, the use

of PR contact lenses together with MPS has become the most popular options in

Hong Kong. Contact lens practitioners want low cost bifocal/multifocal contact

lenses with better visual performance and toric lenses with a wider range in

parameters. The use of RGP lenses and EW SH lenses are limited and only a small

percentage of practitioners prescribe overnight ortho-k treatment. Ocular dryness

during contact lens wear was reported to be the major complaint of contact lens

wearers. The main source of contact lens information came from communication

with suppliers. Time constraints and limited varies of continuing education

courses have restricted the usefulness of this source of information to practitioners.




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                                                                           Chapter 6




Chapter 6

Microbial Contamination of Soft
Contact Lenses, Lens Cases and Lens
Care Solutions


6.1 Aims

Microbial keratitis is a virulent disease that can cause serious corneal damage and

lead to blindness. Contact lens wear, especially EW, is a well known risk factor in

the development of microbial keratitis (see Section 2.3). It has been suggested that

contact lens wear introduces pathogens to the cornea, as keratitis-inducing

pathogens are commonly isolated from contaminated contact lenses or lens cases

used by patients (see Section 3.1 and 3.2). Therefore, the assessment of

contamination of contact lenses and lens care accessories, including lens cases and

lens care solutions, is important in the study of the aetiology of contact

lens-associated microbial keratitis.

Many studies have been carried out to determine levels of contamination of

contact lenses, lens cases and lens care accessories (see Sections 3.2 to 3.4).

However, with the introduction of new contact lens materials, lens designs and

newly-formulated lens care solutions, the mode of contact lens use and lens care

have changed considerably. The introduction of SH lenses has allowed continuous

wear for up to 30 days and there are claims that newly-formulated disinfecting

solutions are effective with only a short period of soaking time. Therefore, regular


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                                                                            Chapter 6


monitoring of the microbial contamination associated with contact lens wear is

important, especially in population with high prevalence of contact lens wearers,

and in regions where the climate is hot and humid which favours the growth of

microorganisms.

The aims of this part of the study were to evaluate the contamination rates and to

identify microorganisms associated with the contamination of contact lenses, lens

cases and lens care solutions used by a group of young, university students who

were asymptomatic soft contact lens wearers.



6.2            Ethics Approval

Ethics clearance was obtained from the Human Ethics Sub-Committee of The

Hong Kong Polytechnic University before commencing the study. All subjects

gave informed consent (see Appendix III) before participating in this study.



6.3            Methodology

6.3.1          Subject recruitment

A total of 101 soft contact lens wearers were recruited to participate in this study.

All were asymptomatic and had no history of ocular complications within the last

six months. They were divided into two groups according to their experience with

soft contact lenses.

Group 1: Seventy-five wearers using biweekly, monthly and conventional contact

lenses. All subjects had been wearing soft contact lenses for at least one year.

Group 2: Twenty-six wearers, including daily disposable lens wearers, new

wearers (contact lens experience less than one year) or occasional wearers




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                                                                            Chapter 6


(wearing contact lenses less than four days per week). These subjects were

grouped separately because their use of contact lenses and their handling habits

were likely to be different from experienced and regular soft lens wearers.



6.3.2          Sample collection

Subjects were asked to attend a contact lens consultation wearing their contact

lenses and to bring their lens case and bottle(s) of opened saline solution. If they

did not use saline, they were asked to bring the bottle(s) of solution that they were

currently using for rinsing and soaking their contact lenses.

At the consultation visit, each subject was interviewed to collect personal

information and their contact lens wearing history. Information collected included

contact lens experience (years), type and power(s) of the contact lenses used,

wearing time, wearing schedule, lens care regimen, lens replacement schedules,

problems associated with contact lens wear and their lens handling procedures.



Before removing the lenses, lens surfaces and fitting were examined by slitlamp

biomicroscopy. For each subject, the contact lens was removed aseptically from

the right eye with the subject looking towards the nasal side without blinking.

Using sterilized plastic forceps with soft plastic covered tips, the right lens was

moved gently to the conjunctiva and then removed. On removal, the lens was

placed immediately in a labelled bijou bottle containing 2ml of sterile

phosphate-buffered saline (PBS). The bijou bottle was capped and vortexed

vigorously for 30 seconds to loosen any microorganisms adhering to the lens

surface. After vortexing, the contact lens was removed from the bijou bottle with




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sterilized forceps and returned to the subject. The lens extract in the bijou bottle

was used for microbiological culture.

The solution (if any) in the contact lens case was poured away and the right

chamber of the lens case was filled with 2ml of sterile PBS. The case was closed

tightly and vortexed vigorously for 30 seconds. After mixing, the PBS from the

lens case was transferred into another bijou bottle and labelled appropriately. This

bottle of case extract was used for microbiological culture.

A 2ml solution was withdrawn from the solution bottle that the subject had

brought to the examination, and transferred directly into another labelled bijou

bottle for analysis.



6.3.3           Microbiological techniques

Collected lens extract, case extract and solution samples were transferred to the

laboratory for microbiological examination within 30 minutes after collection.

Organisms were cultured on 5% horse blood BA, CHO, SDA (OXOID

laboratories, Inc.) and Neomycin blood agar (NEO). BA was used for the culture

of most microorganisms; CHO for fastidious organisms; NEO for the culture of

anaerobes and SDA for the isolation of fungi.

Small volumes (0.2 ml) of each collected specimen were inoculated onto separate

agar plates and spread out with a sterile glass ‘hockey stick’ for better absorption.

Spread BA and SDA plates were incubated at 35°C for 72 hours, CHO plates were

incubated at 35°C for 72 hours with 5% CO2, NEO plates were incubated at 35°C

for 48 hours under anaerobic condition.




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                                                                          Chapter 6


For cultures showing growth, the number of colonies on the agar plate was

counted and the colonial morphology was recorded. Positive cultures were

isolated, gram-stained and identified to the genus level, using biochemical tests.

These tests included the oxidase, coagulate, catalase, motility, indole,

oxidation/fermentation and carbohydrate fermentation tests. Rapid One System

and Rapid NF Plus System (Biomerrieux), which are commercial kits

incorporating arrays of biochemical tests were used for the identification of

contaminants, which could not be identified with the above tests. These kits own

set up in accordance with the manufacturer’ instructions and the identity

determined by recording results of the tests in a formatted table which yielded a 7

digit code. This code was used to find the identity from a data book.



6.3.4          Statistical analyses

Statistical analysis involved the Chi-square test, Fisher’s Exact test or the

Mann-Whitney U test where appropriate. Analyses were carried out using SPSS

v12.0 computer statistical software.



6.4            Results:

6.4.1          Subject demographics

A total of 101 soft contact lens wearers participated in this part of the study,

including 75 (63 females; 12 males) from Group 1 and 26 (20 females; 6 males)

from Group 2. A summary of the subject demographics is shown in Table 6.4.1.




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                                                                               Chapter 6


Table 6.4.1. Subject demographics.

                                              Mean ± SD (Range)
                                                 Group 2
                                                 (N=26)                       Overall
                    Group 1      Disposable
                                                   New          Occasional    N = 101
                     N = 75         lens
                                                  wearers        wearers
                                  wearers
                                                  N = 11         N = 11
                                   N=4
                   21.3 ± 1.8     21.0±3.5       20.5 ± 1.5      21.0±1.5    21.1 ± 1.8
Age (years)
                    (18 – 28)     (18 – 26)      (19 – 23)       (18 – 24)    (18 – 28)

CL experience       3.8 ± 2.1     3.0 ± 1.8       0.5 ± 0.2      2.3 ± 1.2    3.3 ± 2.2
(years)             (1 – 10)       (1 – 5)      (0.25 – 0.75)     (1 – 5)    (0.25 – 10)

Wearing schedule    6.0 ± 1.0     2.8 ± 2.9       4.8 ± 1.8      2.7 ± 0.6    5.4 ± 1.6
(Days/week)          (4 – 7)       (1 – 7)         (1 – 7)        (1 – 3)      (1 – 7)

Wearing time       11.0 ± 2.2    10.0 ± 1.6      10.7 ± 2.0      8.5 ± 1.9   10.7 ± 2.2
(Hours/day)          (4 – 7)      (8 – 12)        (8 – 14)       (6 – 12)      (6-16)



According to the responses from the interviews, all subjects were satisfied with

their contact lenses and their lens care system. Most subjects understood the use of

their lens care solutions and, with few exceptions, all could disinfect their contact

lenses properly. There were two subjects who used only saline to soak their

contact lenses. One was a daily disposable lens wearer who did not dispose of her

contact lenses after wear, but soaked them overnight in saline and occasionally,

reused them for another day. The other was a monthly disposable lens wearer, who

did not know the difference between MPS and saline, and used saline to soak her

contact lenses overnight. She admitted that she learned how to clean and disinfect

her contact lenses from her friends and not from qualified contact lens

practitioners. Another subject did not pour away used MPS in the lens case after

lens disinfection and reused it to soak her contact lenses a few more times. She

explained that she did not know that the disinfecting power of MPS deteriorates

every time after use and she thought it would be strong enough for multiple usages.

Another subject did not close the wells of her lens case during lens disinfection,


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                                                                              Chapter 6


because she did not want to buy a new lens case after losing the caps of her lens

case. The risks of serious complications with improper use and care of contact

lenses was explained to these subjects, and they were re-educated regarding the

proper use and care of contact lenses, after the samples were collected.



6.4.2            Incidence of microbial contamination

At least one tested sample from each of 45 out of 101 contact lens wearers (45%)

was contaminated. All contaminants isolated were bacteria; no fungi were found.



Table 6.4.2 Number and percentage of subjects with contaminated samples.


                                                                  Samples contaminated
                                         Including all samples        by potential
                                         with positive cultures       pathogenic
                                                                    microorganisms

Subjects with no contaminated sample           56 (55%)                 66 (65%)

Subjects with one contaminated sample          22 (22%)                 17 (17%)

Subjects with two contaminated samples         23 (23%)                 18 (18%)

Total                                         101 (100%)               101 (100%)




The number and percentage of subjects with different numbers of contaminated

samples are shown in Table 6.4.2. A total of 22% of our subjects have one

contaminated sample and the other 23% of them have two contaminated samples.



Since our objective was to determine lens care habits that would increase potential

risk (safety) of contact lens wear, in the following analyses only items which were

contaminated by potentially pathogenic microorganisms were considered as

contaminated. Those samples associated with microorganisms that were



                                                                                    101
                                                                                                       Chapter 6


non-pathogenic to the ocular surface such as Nesseria, Micrococci,

Flavobacterium, CNS and Comamonas acidovorans were not considered as

contaminated. A total of 17% of our subjects have one sample and the other 18%

of them have two samples contaminated by potential pathogenic microorganisms.



Table 6.4.3. Incidence of microbial contamination.




                                           Group 1              Group 2                Overall          p


Lens           Positive culture           4/75 (5%)            5/26 (19%)            9/101 (9%)
                                                                                                      0.009†
extracts       Negative culture          71/75 (95%)          21/26 (81%)           92/101 (91%)

Case           Positive culture          22/75 (29%)         11/23* (48%)           33/98* (34%)
                                                                                                      0.101
extracts       Negative culture          53/75 (71%)         12/23* (52%)           65/98* (66%)

Solution       Positive culture           9/75 (12%)          2/23* (9%)            11/98* (11%)
                                                                                                      0.661
samples        Negative culture          66/75 (88%)         21/23* (91%)           87/98* (89%)

* Excluding 3 daily disposable lens wearers who did not use any lens case or lens care solution.
p − probability values of χ2 Test for contamination rate differences between Group 1 and 2 subjects
† Significant at the 0.05 level




A total 101 lens extracts (four daily, 33 bi-weekly, 29 monthly and 35

conventional lenses), 98 case extracts and 98 solution samples (66 MPS and 32

saline) were tested. A summary of contamination rates of each tested sample is

shown in Table 6.4.3. For the samples tested, 9% of lens extracts, 34% of case

extracts and 11% of solutions were contaminated with potential pathogenic

bacteria. Compared with contact lenses and solutions, lens cases were more likely

to be contaminated.



Contamination rates of lens extract was significantly different between Groups 1

and 2 (χ2 = 6.814, df = 1, p = 0.009) (Table 6.4.3). Contact lenses collected from

Group 2 were more likely to be contaminated than those from Group 1. However,


                                                                                                               102
                                                                          Chapter 6


no such difference was found in case extracts and lens care solutions (χ 2 = 2.695,

df = 1, p = 0.101; χ 2 = 0.193, df = 1, p = 0.661) (Table 6.4.3).



6.4.3 The effect of contact lens usage and lens care habits on
      microbial contamination

Statistical analyses were performed to investigate the association between contact

lens experience and lens wearing time (hours per day) and wearing schedule (days

per week) on the contamination rate of the tested samples. Analyses were

performed after excluding daily disposable lens wearers and those who were

unable to provide accurate information.




                                                                               103
                                                                                                                     Chapter 6


Table 6.4.4 Association between contact lens experience, wearing schedules and the
age of items, of subjects with and without contaminated items.


                                   Lens extract                     Case extract                         Solution

                                           Sterile or                        Sterile or                               Sterile or
                                              only                              only                                     only
                             Contaminated associated           Contaminated associated         Contaminated           associated
                                          with normal                       with normal                              with normal
                                             flora                             flora                                     flora


Contact lens   Median               2                 3             4                2.75            5                    3
experience     (Range)          (0.5 − 7)        (0.25 − 10)   (0.25 − 10)       (0.25 − 10)     (0.5 − 9)           (0.25 − 10)
(years)
               N                    9                 88           33                 64            11                   86

                                        p = 0.930                         p = 0.464                      p = 0.016†
Wearing        Median               4                  6            6                 6              6                    6
schedules      (Range)           (1 − 7)            (1 − 7)      (2 − 7)           (1 − 7)        (4 −7)               (1 − 7)
(days/
               N                    9                 88           33                 64            11                   86
week)
                                        p = 0.034†                        p = 0.418                        p = 0.692
               Median              10                  10           10               10            12                    10
Wearing        (Range)          (6 − 16)            (6 − 16)     (6 − 15)         (6 − 16)      (10 − 14)             (6 − 16)
time
(hours/day)    N                    9                 88           33                 64            11                   86
                                        p = 0.098                         p = 0.705                        p = 0.444

               Median                2                4
                                                                             −                                   −
Lens age       (Range)          (0.5 − 24)       (0.5 − 96)
(weeks)                                                 *
               N                    9                82                      −                                   −

                                        p = 0.633                            −                                   −
               Median                                               12                12
                                             −                                                               −
Case age       (Range)                                           (1 − 64)          (1 − 96)
(weeks)                                                               *                    *
               N                             −                     28                 47                     −

                                             −                            p = 0.563                              −

* Excluding 4 daily disposable contact lens wearers and those who could not give accurate information on this item.
p − probability values of Mann-Whitney Test for differences between subjects with and without contaminated items
† Significant at 0.05 level




Significant differences in lens wearing schedules (days per week) were found

between subjects with and without contamination of lens extract (Mann-Whitney

U, p = 0.034) (Table 6.4.4). Significant differences in contact lens experience

(years) were found between subjects with and without contamination of lens care

solution (Mann-Whitney U, p=0.016) (Table 6.4.4). No significant differences in

contact lens experience and lens wearing time (hour per day) were found between

subjects with and without contamination of case extract (Mann-Whitney U, p >




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0.05) (Table 6.4.4). There were no significant differences in the age of contact

lenses and lens cases between subjects with and without contaminated lens extract

or case extract (Mann-Whitney U, p > 0.05) (Table 6.4.4).


Analyses were also performed to test for differences among disinfecting regimens

and lens care habits between contact lens wearers with or without contamination.

Four daily disposable lens wearers, who do not use any disinfecting regimen, lens

case or solution, were excluded from this part of the study.


Table 6.4.5 Effect of disinfecting regimen used and lens care procedures of contact
lens wearers on the contamination rates of tested lenses.


                                                                        Lens extract
                                                         Contaminated              Sterile or only       Odd Ratio (OR)
                                                                                   associated with       95% Confidence
                                                                                    normal flora           Interval (CI)
                             Hydrogen                                                                       OR = 0.7
Disinfecting regimen                                             1                         15
                             peroxide                                                                    95% CI = 0.165 −
used
                             Chemical                          7                     73                      12.569
                                                       χ2 = 0.109, df = 1, p = 0.741 (N = 96*)

                             Biweekly                            5                         28
Lens used
                             Monthly                             2                         27
                             Conventional                      3                     32
                                                       χ2 = 2.076, df = 2, p = 0.354 (N = 97)

                             With cleaner                        2                         21              OR = 0.912
Clean lenses                                                                                             95% CI = 0.176 −
                             Without cleaner                   7                     67                       4.728
                                                       χ2 = 0.012, df = 1, p = 0.912 (N = 97)

Use of saline/MPS to         Rinse                               3                         62               OR = 0.21
rinse lenses after lens                                                                                  95% CI = 0.049 −
cleaning                     No rinse                            6                         26                 0.903
                                                       χ = 5.090 , df = 1, p = 0.024† (N = 97)
                                                        2


Regular use of               Yes                                 4                         55              OR = 0.48
enzymatic protein                                                                                        95% CI = 0.12 −
removal                      No                                5                     33                      1.915
                                                       χ2 = 1.117 , df = 1, p = 0.291 (N = 97)
* Excluding one subject who only used saline
p − probability values of χ2 test for differences between subjects with and without contaminated items
† Significant at 0.05 level




                                                                                                              105
                                                                                                              Chapter 6


Contamination rates of case extract were not affected by the type of disinfecting

regimen used (χ2 = 0.600, df = 1, p = 0.439) (Table 6.4.6). A significant difference

in the contamination rate of case extracts was found between subjects with or

without contaminated lens extracts (χ2 = 13.305, df = 1, p = 0.000) (Table 6.4.6).

Nearly all subjects (eight out of nine) with contaminated lens extracts also have

contaminated case extracts.


Table 6.4.7 Effect of the disinfecting regimen used and solution care procedures of
contact lens wearers on the contamination rates of the tested solutions.


                                                                          Solution

                                                          Contaminated               Sterile or only         Odd Ratio (OR)
                                                                                     associated with         95% Confidence
                                                                                      normal flora             Interval (CI)
                                 Contaminated                      0                         9
Lens extract
                                 Sterile                          11                         77
                                                       p# = 0.592 (N=97)
                                 Contaminated                     10                         23                OR = 27.4
Case extract                                                                                                 95% CI = 3.32 −
                                 Sterile                           1                         63                  226.01
                                                       χ2 = 17.888, df = 1, p = 0.000† (N=97)

The kind of solution             MPS                              11                         55
tested                           Saline                            0                         31
                                                       p# = 0.015† (N=97)
Check the expiry date                                                                                          OR = 1.09
                                 Yes                               7                         53
of lens care solution                                                                                        95% CI = 0.296
regularly                        No                                4                         33                 − 4.011
                                                       χ2 = 0.017 , df = 1, p = 0.897 (N=97)
p − probability values of χ2 test for differences between subjects with and without contaminated items
p# - probability values of Fisher’s Exact test for difference between subject with and without contaminated items
† Significant at the 0.05 level




The solution contamination rate of subjects with contaminated case extracts was

significantly different from subjects without contaminated case extracts (χ2 =

17.888, df = 1, p = 0.000) (Table 6.4.7) but no such difference was found between

subjects with or without contaminated lens extract (Fisher’s Exact test, p = 0.592)

(Table 6.4.7). There were statistically significant differences between


                                                                                                                    107
                                                                                   Chapter 6


 contamination rates of tested MPS or saline (Fisher’s Exact test, p = 0.015) (Table

 6.4.7). The contamination rate of lens care solutions was not different between

 subjects who did or did not regularly check the expiry date of their lens care

 solution (χ2 = 0.017, df = 1, p = 0.897) (Table 6.4.7).



 6.4.4               Isolated contaminants

 A total of 14 different species of bacteria were isolated from contaminated samples.

 The distribution of contaminants is shown in Figure 6.4.1.




            Lens extract                      Case extract                     Solution


           X. maltophilia

                Serratia

              S. aureus

    Other Pseudomonas

          P. aeruginosa

               Nesseria

              Moraxella

             Micrococci

              Klebsiella

         Flavobacterium

                  E. coli

                    CNS

Comamonas acidovorans

      Alc. xylosoxidans

         Acinetobacter

                            0   2   4     6        8         10     12   14   16     18         20
                                                    No. of isolations




 Fig 6.4.1 Bacteria isolated from contaminated samples.




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                                                                           Chapter 6


There were 8 different contaminants isolated from lens extracts, 11 from case

extracts and 9 from lens care solutions (Figure 6.4.1). Potential pathogens of

keratitis such as S. aureus, Serratia and P. aeruginosa were cultured from the

tested samples. The predominant contaminant was Serratia, followed by CNS, S.

aureus, Acinetobacter and Flavobacterium (Figure 6.4.1). S. aureus was the most

frequently isolated contaminant from lens extract, whereas Serratia was the most

common contaminant isolated from case extract and lens care solutions.

Case extracts were associated with the highest incidence of mixed contamination.

More than one genus of bacterium was isolated from 36% (12/33) of contaminated

case extracts - up to three different genera of bacteria were found in a single case

extract sample. The percentage of contaminated lens extracts associated with

mixed contaminants was 22% (2/9) and for contaminated solutions was 27%

(3/11). The same genera of contaminants were isolated from contaminated

samples of 50% (9/18) subjects with two contaminated samples. They were found

either from lens extracts and case extracts or from case extract and solutions but

not from lens extract and lens care solutions of the same subject.




6.5            Discussion

In this part of the study, the contamination rates and microorganisms associated

with the contaminated contact lenses and lens care accessories were investigated.

In addition, it was attempted to ascertain risk factors associated with the

contamination of the tested items. The results reflected the contact lens hygiene of

a group of young, university based, and asymptomatic soft contact lens wearers.

Nearly half of our subjects (45%) had at least one contaminated tested sample, and

23% have two contaminated tested samples. The contamination rate of lens extract,


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                                                                           Chapter 6


case extract and lens care solution contaminated by ocular pathogenic

microorganisms was 9%, 34% and 11%.



Subjects were divided into two groups to study the effect on the contamination

rates of the tested items according to their contact lens experience and how they

use their contact lenses. Significantly higher contamination rates of lens extract

were found from the Group 2 lens wearers − a group of daily

disposable/new/occasional lens wearers (Table 6.4.3). However, no such

differences were found between the contamination rates of case extracts and lens

care solutions of these two groups. This indicates that contact lenses used by

Group 2 subjects are more likely to be contaminated. Hand, lower eyelid and

domestic water supply are recognized sources of contaminants (Willcox et al.,

1997). Contaminants from these sites are transported onto contact lenses and lens

cases through hand contacts (Hart & Shin, 1987). Experienced and regular contact

lens wearers are more skilful in handling their contact lenses, and this may help to

prevent their contact lenses becoming contaminated. Since Group 2 was formed by

small numbers of daily disposable lens wearers and new and occasional lens

wearers, no meaningful analysis between contamination rates of each subgroup

could be made. Further investigation with more subjects would be required to

perform separate analyses of each subgroup.



All solution samples collected in this study were preserved lens care solutions. The

results show that it was not unusual for any of the solutions, including preserved

saline and MPS to be contaminated. No comparison of contamination rates of lens




                                                                                110
                                                                            Chapter 6


care solutions among different brands was made, as the number of subjects using

particular brands of solution was too small for meaningful analysis.



Compared with previous studies (See Table 3.1.1), the contamination rates of

contact lens and lens care accessories obtained in this study are relatively low.

However, these differences in contamination rates may be due to the differences in

subject selection and in the culturing method used. Our subject groups were

formed of young, well-educated and healthy contact lens wearers. Therefore, a

lower contamination rate may be expected, as they are assumed to have better

knowledge on the importance of lens hygiene, compared with the general

population. Moreover, a lower contamination rate in the lens extract may be

expected as we cultured lens extracts made from contact lenses removed from eyes

rather than from cases. Contact lenses on eyes are protected from contamination

by the washing effect of tears and blinking (McClellan et al., 1997). In this study,

contact lenses were returned to our subjects, and contact lenses were not cultured

directly. This may allowed some firmly attached contaminants on contact lenses

being missed. According to the study of Hart et al., (1993), the contamination rate

could be lower by around two per cent (2 in 108), if no direct culture of the contact

lenses was performed.



Analyses were performed to study the effect of contact lens usage and lens caring

habits on the contamination of contact lenses and lens care accessories. Significant

differences in the number of days of lens wear per week were found between

subjects with or without contaminated lens extract (Table 6.4.5). Our results show

that contact lenses used by occasional wearers are more likely to be associated



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                                                                           Chapter 6


with pathogenic microorganisms. This may be because contact lenses that are left

in the case, without being used for a period of time, are in a favourable

environment for the build-up of biofilm (McLaughlin-Borlace et al., 1998).

Contaminants shielded by the biofilm are more firmly attached to lens surfaces.

Lens care solutions of contact lens wearer with longer contact lens experience

were found more likely to be contaminated by ocular pathogens (Table 6.4.5). This

may because the level of compliance of contact lens wearers deteriorated with the

duration of contact lens use (Efron et al. 1997). However no such effect were

found on the contamination rate of contact lenses and lens cases according to the

experience of contact lens wearers and the period that these items had been used.

Using saline or MPS to rinse lenses after cleaning contact lenses were found to be

effective in lower contact lenses contamination by pathogenic microorganisms

(Table 6.4.6), It is easy to understand why the rinsing of contact lenses helps to

prevent contamination of contact lenses, since rinsing of lenses help to remove

contaminants effectively. Although not reaching statistical significant, regular use

of cleaner, or enzymatic protein removal had an OR indicating a protective effect.

The contamination rates of lens extracts and case extracts were not affected by the

type of contact lenses or the disinfecting regimen used (Table 6.4.6 and Table

6.4.7). Although results for use of disinfecting regimen do not reach statistical

significant level, the use of hydrogen peroxide appears to be better than MPS.

Discarding solution and air dry lens cases, and regular cleaning of lens case have

protective effect. Surprising, replacement of the lens case did not appear to be

important in reducing contamination with OR = 1.49. Tested MPS were

significantly more likely to be contaminated than saline (Table 6.4.8). This may

because saline solution was simply used for rinsing, where MPS were designed for



                                                                                112
                                                                           Chapter 6


multiple purposes including cleaning, rinsing and storing of contact lenses. Since

contamination was suggested to be associated with subject handling

(Mowrey-McKee et al., 1992), MPS solutions having more contact with contact

lens wearers were more likely to be contaminated than saline even though they

were inbuilt with disinfectants. The sensitivity of the analyses in this part of the

study were limited by our sample size, since out of 97 subjects there were only 9

subjects with lens extracts, and 11 subjects with lens care solutions being

contaminated by ocular pathogenic microorganisms. In addition, our subjects were

university students, so checking of expiry date may be done more routinely on

purchase and solution would tend to be used up before expiry.



Nearly all subjects with contaminated lens extracts were also found to have

contaminated case extracts (Table 6.4.6); while most subjects with contaminated

solutions also had contaminated cases (Table 6.4.8). This indicates that there is

some degree of cross contamination between the contact lenses and the lens case

or between lens case and lens care solutions. This was further supported by the

frequent isolation of the same genera of bacteria from the lens extract and the case

extract, and from the case extract and the solution used by the same contact lens

wearers. No such correlation was found between contact lenses and the lens care

solution.



Contaminants found in this study included pathogens which may induce contact

lens-associated microbial keratitis, normal flora of the ocular surfaces, the

gastrointestinal tract, the skin, and the environment. Serratia, CNS and S. aureus

were the most common contaminants isolated from the tested items. In agreement



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                                                                         Chapter 6


with Mayo et al., (1987), Serratia was the most common contaminant isolated

from preserved lens care solutions. Other potential keratitis-inducing pathogens,

such as S. aureus and Pseudomonas were also isolated from the contaminated

samples. Others contaminants included Acinetobacter, Flavobacterium and X.

malthopilia, which are widely distributed in nature were also isolated.

Gastrointestinal tract flora such as E.coli and Klebsiella were isolated from lens

extracts and case extracts.

The lens case is the most heavily contaminated items and up to three different

genera of bacteria were found in some contaminated case extracts. This may

because, as mentioned previously, the lens cases are favourable environment for

the formation of biofilm than contact lenses (McLaughlin-Borlace et al. 1998). It

provides attachment sites for the adhesions of microorganisms (Willcox et al.,

2001) and physically protects them from disinfectants (LeChevallier et al., 1988).



6.6            Conclusion

Contact lenses and lens care accessories of around half of our subjects were found

to be contaminated. Lens cases were the most frequently and most heavily

contaminated items, up to three different genera of bacteria being found from a

single contaminated case extract. Contact lenses and lens cases used by daily

disposable/new/occasional wearers are more likely to be contaminated, and a

higher contamination rate was found with contact lenses used on an

occasional-wear basis and lens care solution used by contact lens wearers with

longer contact lens experience. Rinsing contact lenses with either saline or MPS

after cleaning was found to be an effective way to prevent contact lens

contamination. The contamination of MPS was more common than the



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                                                                           Chapter 6


contamination of saline, although MPS were protected by preservatives and

disinfectants. Our results suggest that there is cross contamination between contact

lenses and lens cases, and between lens cases and lens care solutions. Potential

keratitis-inducing pathogens are commonly isolated from contact lenses, lens

cases and lens care solutions. The findings reported here also demonstrate that

contact lenses, lens cases and lens care accessories are not well maintained by

contact lens wearers. Therefore, regular reviews and reinforcement of lens care

procedures is essential and the development of stronger disinfecting solutions may

be required.




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                                                                          Chapter 7




Chapter 7

Longitudinal study on the effect of a
compliance       enhancement       strategy
(self-review exercise) on the level of lens
care compliance and contamination of
contact lenses and lens care accessories

7.1 Aims

The presence of ocular signs and symptoms during contact lens wear correlates

with the level of compliance (Collins and Carney, 1986). Contamination of contact

lenses and lens care accessories is thought to be a result of non-compliance with

lens care maintenance regimens (Wilson et al., 1990; Mowrey-Mckee et al., 1992).

It is likely that the ocular complications are induced by the contaminated contact

lenses. To improve the safety of contact lens wear, a better understanding of the

compliance by contact lens wearers is both important and necessary (Trick, 1993).

In addition to the observation of the level of compliance, it is possible that

compliance can be improved by some form of enhancement education.

In this part of the study, the aims were to evaluate the level of compliance and to

identify non-compliant behaviour in a group of young, healthy, university-based,

contact lens wearers, and to evaluate the effectiveness of a compliance

enhancement strategy (self-reviewed exercise) in improving the level of

compliance of contact lens wearers.




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                                                                          Chapter 7



7.2 Ethics approval

Ethics clearance was obtained from the Human Ethics Sub-Committee of The

Hong Kong Polytechnic University before commencing the study. All subjects

gave informed consent (See Appendix III) before participating in this study.



7.3 Methodology

7.3.1 Subject recruitment

Excluding daily disposable lens wearers, sixty-five subjects, who participated in

the second stage of this study agreed to take part in this component.



7.3.2 Compliance assessment by questionnaire

On the first visit, all subjects were asked to complete a self-administrated

questionnaire (Appendix IV). This questionnaire included 15 lens care procedures,

which were divided into five general categories⎯cleaning (3 questions),

disinfecting (4 questions), accessories care (6 questions), enzymatic cleaning (1

question) and replacement schedule (1 question). All of these lens care procedures

were applicable to both hydrogen peroxide and MPS lens care regimens.

Subjects were asked to grade themselves according to how often they carried out

each of these lens care procedures. Except for question 14, a scale from 1 to 4 was

used to grade responses. This scale represents how diligently each lens care

procedure had been carried out ⎯ with 1 for always (total compliance), 2 for often,

3 for sometimes and 4 for seldom (complete non-compliance). For question 14,

subjects were asked whether they carried out regular enzymatic cleaning (once per

week) or use MPS with inbuild enzymatic cleaning agent. Subjects received a



                                                                               117
                                                                               Chapter 7


score of 1, if their answer was “yes”; and a score of 4, if their answer was “no”.

Subjects with non-compliance scores higher than or equal to three were considered

to be non-compliant with that lens care procedure. This level was chosen because

it indicates that subjects were non-compliant for at least half of the time.



7.3.3 Compliance enhancement strategy

In the second part, the effect of a compliance enhancement strategy on the level of

compliance was studied. Non-compliance has been shown to be related to the

extent of the knowledge of contact lens wearers about proper lens care (Ky et al.,

1998), and to the duration of the prescription (Claydon and Efron, 1994). In order

to eliminate the effects on compliance of these two factors, and to ensure that the

differences in compliance are due to the effect of the compliance enhancement

strategy, correct lens care instructions were reviewed with all of our subjects after

the collection of compliance data and before they were allocated into different

groups at the end of the first visit. After the first visit, all subjects who agreed to

participate in the longitudinal study were randomly allocated to one of two groups.

Group 1: Received regular aftercare consultations every six months.

Group 2: Received regular aftercare consultations every six months and

participated in a compliance enhancement strategy once every three months.

The compliance enhancement strategy used in this study was a self-review

exercise on the handling of contact lenses and lens care accessories. All subjects

were masked and did not know that they had been allocated to different groups.

Thus, it is a masked, randomized and controlled study.




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                                                                                         Chapter 7



                                    Patient recruitment
                           Subject in the second stage of the study
                          were invited to take part in this part of the
                                             study




                                 First (initial) appointment
               − Patients were interviewed on their use of contact lenses
               − Ocular examination with slit lamp biomicroscope
               Sample collection
               ∗ Administered in a questionnaire on lens care procedures
               ∗ Collected samples (lens extract, case extract and lens care
                  solution) for microbial examination
               − Re-educated all subjects with standard lens care procedures




           Randomly allocated subjects into
                  Groups 1 and 2




                                                                          Group 2 only
                 Group 1 and Group 2


                                                               ∗ Three-month self-review
                                                                 exercise
                                                                 delivered and returned
                                                                 through e-mail

                                                               ∗ Six-month self-review
         Six-month aftercare appointment                         exercise



                                                               ∗ Nine-month self-review
                                                                 exercise
                                                                 delivered and returned through
                                                                 e-mail
        Twelve-month aftercare appointment
      ∗ Administered in a questionnaire on lens
         care procedure
      ∗ Collected samples for microbial
         examination




Figure 7.3.1 Flow chart of study procedures.



                                                                                             119
                                                                              Chapter 7


The same questionnaire (Appendix IV) was used as the self-review exercise of the

compliance enhancement strategy. The additional self-review exercises were

delivered to Group 2 subjects by e-mail or by hand once every 3 months (Figure

7.3.1). They were asked to complete and return the questionnaires, and to ensure

that they reviewed the whole list of lens care procedures carefully and evaluated

their own lens care procedures.

The level of compliance of each subject was assessed, based on the data collected

from this questionnaire and the microbial culture of the contact lenses and lens

care accessories.



7.3.4 Microbial examination of contact lens and lens care
      accessories
On the first and final visits, contact lenses (right lens only), lens case and lens care

solutions were collected for microbial examination. Only items from which

pathogenic microorganisms were cultured were considered as contaminated.

Sample collection and laboratory culture techniques used in this part of the study

were similar to those used in Sections 6.3.2 and 6.3.3.



7.3.5 Statistical analyses

Mann Whitney U test was applied to investigate the differences between the

non-compliance scores for Groups 1 and Group 2. Non-parametric statistics were

applied because the data did not display a normal distribution.




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                                                                                                          Chapter 7



                    7.4 Results

                    7.4.1 Study population

                    Sixty-five contact lens wearers (14 males and 51 female) accepted our invitation

                    and participated in this part of the study. The mean ± age of the subjects was 21.22

                    ± 1.66 years, and the mean ± contact lens experience was 3.61 ± 2.36 years. The

                    majority of subjects were using chemical disinfecting regimen (85%), whereas the

                    others were using a hydrogen peroxide system (15%). There were 34% subjects

                    using biweekly disposable, 29% using monthly disposable and 37% using

                    conventional contact lenses.


                    7.4.2 Overall non-compliance

                    The questionnaire indicated that all (100%) of our subjects (65/65) were

                    non-compliant to some degree. All of them failed in at least one lens care

                    procedures. The number of non-compliant lens care procedures per subject ranged

                    from one to 11.


                                            Number                               Cumulative number

                    70

                    60

                    50
Number of subject




                    40

                    30

                    20

                    10

                     0
                          1      2      3         4        5       6        7        8        9      10     11

                                               Number of non-compliant lens care procedures


                    Figure 7.4.1 Distribution of subjects according to the number of non-compliant lens
                    care procedures.


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                                                                                                                          Chapter 7


               Over half of the subjects (39/65, 60%) were found to be non-compliant with at

               least six lens care procedures (Figure 7.4.1).



               7.4.2.1            Non-compliant lens care procedures identified

               Most of the non-compliant lens care procedures identified were associated with

               care of accessories. The percentages of compliant and non-compliant subjects for

               each lens care procedure are summarized in Figure 7.4.2.



                                                      Percentage of non-compliant subjects (non-compliance score greater than 2)
                                                      Percentage of compliant subjects (non-compliant score less than or equal to 2)
             100

             90

             80

             70

             60
Percentage




             50

             40

             30

             20

             10

              0
                    1         2        3        4       5        6        7        8   9       10       11      12       13      14       15
                                                                     Lens care procedures#



               # The corresponding lens care procedures:

                        1.   Wash hands with soap before handling contact              8.    Discard solution and air dry lens case after lens
                             lenses                                                          insertion
                        2.   Clean contact lenses after lens removal                   9.    Clean lens case with MPS/cleaner/saline everyday
                        3.   Rinse lenses with lens care solution after cleaning       10.   Disinfect lens case weekly
                        4.   Fill lens case with adequate disinfecting solution        11.   Change lens case every three months
                             as indicated                                              12.   Recap solution bottles every time after use
                        5.   Rinse lenses with MPS/saline before lens insertion        13.   Check the expiry dates of lens care solutions
                        6.   Disinfect contact lenses for time recommended or                regularly
                             longer                                                    14.   Use MPS containing enzymatic cleaning agent or
                        7.   Re-disinfect contact lenses, if they have been left             carry out enzymatic cleaning at least once a week
                             in case as longer than indicated                          15.   Change contact lenses regularly as indicated


                        Figure 7.4.2 Percentages of non-compliant and compliant subjects for each lens care
                        procedure.




                                                                                                                                 122
                                                                                 Chapter 7


With regard to daily cleaning procedures, 34% of the subjects did not clean their hands

before they handled their contact lenses; 35% did not clean their contact lenses; 17%

did not rinse their lenses with contact lens solution after cleaning.

With regard to disinfection, 3% of the subjects did not fill their contact lens case with

adequate solution as indicated; only 39% did not rinsed their contact lenses every time

before lens insertion; 11% did not disinfected their contact lenses for the time indicated

or longer; 74% did not re-disinfect their contact lenses after they had been left in the

case longer than indicated.

With regard to accessories care, 55% of the subjects did not discard the solution and air

dry the lens case; 65% did not clean their lens case everyday; 85% did not disinfect

their lens case weekly; 66% did not change their lens cases every three months; 5% did

not recap their solution bottles after use and 54% did not check the expiry dates of their

lens care solutions regularly.

With regard to enzymatic cleaning, 37% of the subjects neither used MPS with

contained enzymatic cleaning agent nor carried out enzymatic cleaning regularly.

With regard to the lens replacement schedule, 22% of the subjects did not change their

contact lenses regularly as instructed.



Lens extract, case extract and lens care solutions were collected for microbiological

assessment. Forty-two percent (27/65) of our subjects had either contact lenses or lens

care accessories contaminated by microorganisms. In total, 6% (4/65) of contact lenses,

40% (26/65) of lens cases and 14% (9/65) of lens care solutions were contaminated

(Table 7.4.1).




                                                                                      123
                                                                                                   Chapter 7


Table 7.4.1 Incidence of microbial contamination in contact lenses, lens cases and lens
care solutions at the first visit (all subjects).


                                             No. of contaminated samples / No. of tested samples

Lens                                                                4/65

Case                                                               26/65

Solution                                                            9/65




7.4.3 Compliance enhancement strategy

In the second part of the study, we studied the effect of compliance enhancement

strategy on the level of compliance. After receiving a standard review of their lens care

procedures, subjects were randomly allocated into two groups. Both Group 1 and 2

subjects received their regular consultation every six months; where as Group 2

received the additional compliance enhancement strategy once every three months.



Table 7.4.2. Subject demographics of Group 1 and 2.


                                                     Group 1               Group 2
                                                                                                    p
                                                 Mean ± SD            Mean ± SD
                                                Median (Range)       Median (Range)


                                                      21.2 ± 1.6          21.3 ± 1.8
Age (years)                                                                                        0.879
                                                    21 (20 - 27)        21 (19 - 28)

                                                       4.1 ± 2.3          3.3 ± 2.4
CL experience (years)                                                                              0.190
                                                    4 (0.5 - 10)       2.25 (0.5 - 10)

Wearing Schedule                                     5.8 ± 1.3             5.3 ± 1.7
                                                                                                   0.230
(Days/week)                                          6 (3 - 7)             6 (1 - 7)

Wearing Schedule                                     10.9 ± 2.1             10.7 ± 2.2
                                                                                                   0.765
(Hours/day)                                         10 (6 - 16)            10 (8 - 16)
p – probability values of unpaired Student t test




                                                                                                           124
                                                                               Chapter 7


A total of 60 subjects completed the 12-month study, including 30 (26 females; 4 males)

in Group 1 and 30 (21 female; 9 males) in Group 2. Data from four subjects who did not

attend the 12-month aftercare visit and one who changed to daily disposable lenses

were excluded from this part of the study. A summary of the subjects' demographics is

shown in Table 7.4.2. No significant differences in the mean age (unpaired Student t

test: t-value = -0.153, p = 0.879), contact lens experience (unpaired Student t test:

t-value = 1.327, p = 0.190), wearing schedule (days per week) (unpaired Student t test:

t-value = 1.288, p = 0.230), ands wearing time (hours per day) (unpaired Student t test:

t-value = 0.3, p = 0.765) were found between Groups 1 and 2.




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                                                                                                       Chapter 7


Table 7.4.3 Non-compliance scores for each lens care procedure between the two groups
of subjects at baseline.



                                                                  Group 1                 Group 2        p

                                                              Mean ± SD               Mean ± SD
                Lens care procedures
                                                             Median (Range)          Median (Range)

 1.    Wash hands with soap before handling                     2.27 ± 1.11              1.90 ± 1.03
                                                                                                       0.190
       contact lenses                                           2.0 (1 − 4)              2.0 (1 − 4)

                                                                1.83 ± 1.09              2.03 ± 1.16
 2.    Clean contact lenses after lens removal                                                         0.512
                                                                1.0 (1 − 4)              1.5 (1 − 4)

 3.    Rinse lenses with lens care solution after               1.63 ± 1.03              1.63 ± 0.89
                                                                                                       0.812
       cleaning                                                 1.0 (1 − 4)              1.0 (1 − 4)

 4.    Fill lens case with adequate disinfecting                1.10 ± 1.03              1.20 ± 0.48
                                                                                                       0.248
       solution as indicated                                    1.0 (1 − 3)              1.0 (1 − 3)

 5.    Rinse lenses with MPS/saline before lens                 2.00 ± 1.26              2.53 ± 1.36
                                                                                                       0.129
       insertion                                                1.0 (1 − 4)              2.5 (1 − 4)

 6.    Disinfect contact lenses for time                        1.67 ± 0.80              1.67 ± 0.68
                                                                                                       0.718
       recommended or longer                                    1.5 (1 − 4)              1.0 (1 − 3)

 7.    Redisinfect contact lenses, if they have                 2.93 ± 0.91              2.90 ± 0.88
                                                                                                       0.918
       been left in lens case longer than indicated             3.0 (1 − 4)              3.0 (1 − 4)

 8.    Discard solution and air dry lens case after             2.47 ± 1.31              2.63 ± 1.22
                                                                                                       0.627
       lens insertion                                           2.5 (1 − 4)              3.0 (1 − 4)

 9.    Clean lens case with MPS/cleaner/saline                  2.87 ± 1.17              2.93 ± 1.05
                                                                                                       0.926
       everyday                                                 3.0 (1 − 4)              3.0 (1 − 4)

                                                                3.43 ± 0.68              3.40 ± 0.77
 10. Disinfect lens case weekly                                                                        0.993
                                                                4.0 (2 − 4)              4.0 (2 − 4)

                                                                3.00 ± 1.08              2.73 ± 1.11
 11. Change lens case every three months                                                               0.338
                                                                2.0 (1 − 4)              3.0 (1 − 4)

                                                                1.17 ± 0.38              1.12 ± 0.41
 12. Recap solution bottles every time after use                                                       0.741
                                                                1.0 (1 − 2)              1.0 (1 − 2)

 13. Check the expiry dates of lens care                        2.67 ± 1.03              2.53 ± 1.14
                                                                                                       0.645
     solutions regularly                                        3.0 (1 − 4)              2.5 (1 − 4)
 14. Use MPS containing enzymatic cleaning
                                                                2.30 ± 1.51              2.00 ± 1.44
     agent or carry out enzymatic cleaning at                                                          0.430
     least once a week                                          1.0 (1 − 4)              1.0 (1 − 4)

 15. Change contact lenses regularly as                         1.90 ± 0.84              2.00 ± 1.05
                                                                                                       0.937
     indicated                                                  2.0 (1 − 4)              2.0 (1 − 4)
p – probability values of Mann-Whitney U tests for differences between Group 1 and Group 2 subjects




                                                                                                             126
                                                                                                           Chapter 7


Initial non-compliance scores for each lens care procedure and contamination rates

of contact lenses and lens care accessories were compared between Groups 1 and 2.

No significance differences (Mann Whitney U tests, p > 0.05) were found between

the non-compliance scores for all lens care procedures (Table 7.4.3) and the

contamination rates of contact lenses and lens care accessories for Group 1 versus

Group 2 (Table 7.4.4).



Table 7.4.4 Incidence of microbial contaminants in contact lenses, lens cases and
lens care solutions between Group 1 and 2 at baseline.


                                   Group 1                        Group2
                                                                                                       p
                                    No. contaminated/ No. samples

Lens                                  3/30                           1/30                             0.321

Case                                 12/30                          12/30                             1.000

Solution                              3/30                           6/30                             0.282
p – probability values of Mann-Whitney U tests for differences between Group 1 and Group 2 subjects




7.4.3.1       The level of compliance before and after treatment

At the final visit (12-month visit) the same questionnaire was used to assess the

level of each subject’s compliance. The percentages of compliant subjects for each

lens care procedure at the first and final visits are shown in Figures 7.4.3 (a) to (o).




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                                                                                                                                                                                       Chapter 7




                                    (a) Wash hands before handling contact lenses                                                     (b) Clean contact lenses after lens rem oval

                                                                       Baseline      Final visit                                                                          Baseline      Final visit
                              100                                                                                               100
                               90                                                                                                90
% of compliant subjects




                                                                                                      % of compliant subjects
                               80                                                                                                80
                               70                                                                                                70
                               60                                                                                                60
                               50                                                                                                50
                               40                                                                                                40
                               30                                                                                                30
                               20                                                                                                20
                               10                                                                                                10
                                0                                                                                                 0
                                               Group 1                     Group 2                                                              Group 1                      Group 2




                                  (c) Rinse lenses w ith lens care solution after
                                                     cleaning                                                                    (d) Fill lens case w ith adequate disinfecting solution
                              100                                   Baseline     Final visit                                                            as indicated
                                                                                                                                                                        Baseline    Final visit
                               90                                                                                               100
% of c om pliant s ubjec ts




                               80                                                                                                90
                                                                                                      % of compliant subjects

                               70                                                                                                80
                               60                                                                                                70
                               50                                                                                                60
                               40                                                                                                50
                                                                                                                                 40
                               30
                                                                                                                                 30
                               20                                                                                                20
                               10                                                                                                10
                                0                                                                                                 0
                                             Group 1                   Group 2                                                                   Group 1                   Group 2




                                     (e) Rinse lenses w ith MPS/saline before lens                                                (f) Disinfect contact lenses for time recomm ended
                                                       insertion                                                                                         or longer
                                                                      Baseline     Final visit                                                                         Baseline  Final visit
                              100
                               90                                                                                               100
% of compliant subjects




                               80
                                                                                                     % of compliant subjects




                               70                                                                                                80
                               60
                                                                                                                                 60
                               50
                               40
                                                                                                                                 40
                               30
                               20                                                                                                20
                               10
                                0                                                                                                 0
                                               Group 1                     Group 2                                                             Group 1                      Group 2




                               (g) Redisinfect contact lenses, if they have been left                                             (h) Discard solution and air dry lens case after lens
                                       in lens case for longer than indicated                                                                           insertion
                              100                                       Baseline     Final visit                                                                       Baseline      Final visit
                                                                                                                                100
                               90                                                                                                90
% of compliant s ubjec ts




                                                                                                   % of compliant subjects




                               80                                                                                                80
                               70                                                                                                70
                               60                                                                                                60
                               50                                                                                                50
                               40                                                                                                40
                               30                                                                                                30
                               20                                                                                                20
                               10                                                                                                10
                                0                                                                                                  0
                                               Group 1                     Group 2                                                             Group 1                     Group 2




                                                                                                                                                                                       128
                                                                                                                                                                                    Chapter 7


                                                                                                                                            (j) Disinfect lens case w eekly
                             (i) Clean lens case w ith MPS/cleaner/saline everyday

                                                                                                                                                                      Baseline      Final visit
                                                                    Baseline      Final visit                                 100
                             100
                              90                                                                                               90




                                                                                                    % of compliant subjects
                                                                                                                               80
  % of compliant subjects
                              80
                              70                                                                                               70
                              60                                                                                               60
                              50                                                                                               50
                              40                                                                                               40
                              30                                                                                               30
                              20                                                                                               20
                              10                                                                                               10
                               0                                                                                                0
                                             Group 1                    Group 2                                                               Group 1                     Group 2




                                                                                                                                    (l) Recap solution bottles every tim e after use
                                     (k) Change lens case every three months
                                                                                                                                                                       Baseline     Final visit
                                                                    Baseline      Final visit                                 100
                             100
                              90                                                                                               90


                                                                                                    % of compliantsubjects
                                                                                                                               80
  % of compliant subjects




                              80
                              70                                                                                               70
                              60                                                                                               60
                              50                                                                                               50
                              40                                                                                               40
                              30                                                                                               30
                              20                                                                                               20
                              10                                                                                               10
                               0                                                                                                0
                                             Group 1                    Group 2                                                               Group 1                     Group 2




                               (m ) Check the expiry dates of lens care solutions                                               (n) Use MPS contam ining enzym atic cleaning agent
                                                   regularly                                                                   or carry out enzym atic cleaning at least once a w eek
                                                                  Baseline     Final visit
                                                                                                                                                                     Baseline     Final visit
                             100                                                                                              100
  % of compliant subjects




                                                                                                    % of compliant subjects




                              80                                                                                               80

                              60                                                                                               60

                              40                                                                                               40

                              20                                                                                               20

                               0                                                                                                0
                                             Group 1                    Group 2                                                               Group 1                     Group 2




                                   (o) Change contact lenses regularly as indicated
                                                                       Baseline       Final visit
                             100
                              90
   % of compliant subjects




                              80
                              70
                              60
                              50
                              40
                              30
                              20
                              10
                               0
                                              Group 1                     Group 2




Figure 7.4.3. Graphs (a) to (o) represent the percentage of compliant subjects
(included both Group 1 and 2)for each lens care procedure at the beginning and at
the final visit.


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                                                                                       Chapter 7


Table 7.4.5 Incidence of microbial contamination in contact lenses, lens cases and
lens care solutions for Groups 1 and 2 subjects.


                                Baseline                                  Final
                     No. of contaminated samples /           No. of contaminated samples /
                           No. of tested samples                   No. of tested samples


               Group 1          Group 2            Total   Group 1      Group 2            Total

Lenses              3/30           1/30            4/60     2/30           2/30            4/60

Cases           12/30             12/30            24/60    8/30          10/30            18/60

Solutions           3/30           6/30            9/60     3/30           4/30            7/60



Except for a few lens care procedures, the percentages of compliant subjects for

most lens care procedures increased throughout the study (Figure 7.4.3 (a) to (o)).

For Group 1, the percentage of subjects who cleaned their lens cases with

MPS/cleaner/saline everyday decreased by 10% (from 40% to 30%) at the end of

the study. The percentage of compliant subjects, who recapped their solution

bottles every time after use decreased by 7% (from 100% to 93%) for Group 1 and

by 3% (from 100% to 97%) for Group 2. The percentage of Group 2 subjects, who

changed their contact lenses regularly, decreased by 7% (from 80% to 73%) at the

end of the study.

The number of subjects with contaminated items also decreased from 42% (25/60)

to 38% (23/60). When comparing the first and final visits, there was no change in

the contamination rates of contact lenses, while the contamination rates for lens

cases and lens care solutions were decreased by 10% and 3%, respectively (Table

7.4.5).




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                                                                                                          Chapter 7


7.4.3.2              The effect of compliance enhancement strategy

At the 12-month visit, the non-compliance scores and contamination rates for

Groups 1 and 2 were assessed and compared. Any significant differences in the

non-compliance scores and contamination rates between the two groups were

assumed to be caused by compliance enhancement strategy.

Table 7.4.6 Non-compliance scores for each lens care procedure between the two
groups of subject at final visit.


                                                                     Group 1                 Group 2                  p
                                                                 Mean ± SD               Mean ± SD
                Lens care procedures#
                                                                Median (Range)          Median (Range)
 1. Wash hands with soap before handling contact                   1.57 ± 0.73              1.50 ± 0.86
                                                                                                                 0.453
 lenses                                                            1.0 (1 − 3)              1.0 (1 − 4)
                                                                   1.73 ± 0.98              1.63 ± 0.85
 2. Clean contact lenses after lens removal                                                                      0.811
                                                                   1.0 (1 − 4)              1.0 (1 − 4)
 3. Rinse lenses with lens care solution after                     1.40 ± 0.62              1.33 ± 0.61
                                                                                                                 0.606
 cleaning                                                          1.0 (1 − 3)              1.0 (1 − 3)
 4. Fill lens case with adequate disinfecting                      1.03 ± 0.18              1.03 ± 0.18
                                                                                                                 1.000
 solution as indicated                                             1.0 (1 − 2)              1.0 (1 − 2)
 5. Rinse lenses with MPS/saline before lens                       1.50 ± 0.90              1.80 ± 1.06
                                                                                                                 0.203
 insertion                                                         1.0 (1 − 4)              1.0 (1 − 4)
 6. Disinfect contact lenses for time                              1.47 ± 0.73              1.53 ± 0.63
                                                                                                                 0.486
 recommended or longer                                             1.0 (1 − 4)              2.0 (1 − 3)
 7. Redisinfect contact lenses, if they have been                  3.03 ± 1.07              2.57 ± 0.94
                                                                                                                 0.058
 left in lens case longer than indicated                           3.0 (1 − 4)              3.0 (1 − 4)
 8. Discard solution and air dry lens case after                   1.97 ± 1.10              2.03 ± 1.03
                                                                                                                 0.724
 lens insertion                                                    1.5 (1 − 4)              2.0 (1 − 4)
 9. Clean lens case with MPS/cleaner/saline                        2.97 ± 1.07              2.23 ± 1.00
                                                                                                                 0.008†
 everyday                                                          3.0 (1 − 4)              2.0 (1 − 4)
                                                                   3.30 ± 0.84              3.03 ± 0.89
 10. Disinfect lens case weekly                                                                                  0.200
                                                                   3.5 (1 − 4)              3.0 (1 − 4)
                                                                   2.40 ± 0.93              2.10 ± 0.99
 11. Change lens case every three months                                                                         0.178
                                                                   2.0 (1 − 4)              2.0 (1 − 4)
                                                                   1.10 ± 0.40              1.17 ± 0.46
 12. Recap solution bottles every time after use                                                                 0.750
                                                                   1.0 (1 − 3)              1.0 (1 − 3)
 13. Check the expiry dates of lens care solutions                 2.43 ± 1.17              2.20 ± 1.03
                                                                                                                 0.439
 regularly                                                         2.5 (1 − 4)              3.0 (1 − 4)
 14. Use MPS containing enzymatic cleaning                         2.20 ± 1.49              2.00 ± 1.44
                                                                                                                 0.595
 agent or carry out enzymatic cleaning at least                    1.0 (1 − 4)              3.0 (1 − 4)
            k
                                                                   1.60 ± 0.77              1.80 ± 1.00
 15. Change contact lenses regularly as indicated                                                                0.545
                                                                   1.0 (1 − 3)              1.0 (1 − 4)
p – probability values of Mann-Whitney U tests for differences between Group 1 and Group 2 subjects
† Significant at the 0.05 level



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                                                                                                      Chapter 7



The non-compliance scores of Groups 1 and 2 in the final visit are summarized in

Table 7.4.6, and the contamination rates of contact lenses and lens care accessories

are shown in Table 7.4.7. At the final visit, the only significant difference between

the compliance scores for cleaning lens cases with MPS/cleaner/saline

(Mann-Whitney U test, p = 0.008) between Groups 1 and 2. No significant

differences (Mann-Whitney U tests, p > 0.05) were found for the level of

compliance of other lens care procedures or for the contamination of contact lenses

or lens care accessories between Groups 1 and 2.


Table 7.4.7 Incidence of microbial contamination in contact lenses, lens cases and
lens care solutions at the final visit.


                                    Group 1                        Group 2
                            No. contaminated /              No. contaminated /                    p
                              No. of samples                  No. of samples

Lenses                                2/30                            2/30                       1.000

Cases                                 8/30                           10/30                       0.576

Solutions                             3/30                            4/30                       0.690
p – probability values of Mann-Whitney U tests for differences between Groups 1 and 2 subjects




7.5 Discussion

This study demonstrates that non-compliance with lens care procedures among a

group of young, healthy, university-based soft contact lens wearers is very

common. Our results showed that all of our subjects had some degree of

non-compliance and the use of contaminated contact lenses or lens care

accessories is not uncommon.




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                                                                        Chapter 7



7.5.1 Compliance assessment techniques

Interview, a questionnaire, a health belief model and a demonstration are the

compliance assessment techniques adopted by previous investigators (Collins and

Carney, 1986; Chun and Weissman, 1987; Soni et al., 1995; Coopersmith and

Weinstock, 1997; Ky et al., 1998). In this study, we tried to assess the level of

compliance with a questionnaire in combination with microbial examination. We

included microbial examination in addition to a questionnaire because in the

assessment of compliance, a questionnaire alone may not accurately reflect the

behaviour of a subject in the home environment. The microbial examination serves

as an objective way of assessing the subjects’ compliance. In previous studies

where questionnaire were used (Chun and Weissman, 1987; Sokol et al., 1990),

subjects were usually only asked about whether they did or never did each lens

care procedure. Considering that contact lens wearers may be totally or partially

non-compliant (Efron, 1997), we also took into account the frequency that each

lens care procedure was carried out during our study period. We believe that this

should help to increase the sensitivity of our questionnaire in assessing each

subject’s compliance, and this may be the reason why our results have shown a

higher level of non-compliance, when compared with previous studies (Collins

and Carney, 1986; Chun and Weissman, 1987; Sokol et al., 1990; Turner et al.,

1993a & 1993b; Gower et al., 1994; Ky et al., 1998).



7.5.2 Level of compliance among contact lens wearers

The percentage of compliant subjects is highly dependent on the method of

assessment applied and also on the criteria used to define non-compliance. If we

used the criteria applied by Collins and Carney (1986), all of our subjects were



                                                                         133
                                                                            Chapter 7


non-compliant, as they defined non-compliance as failing in any one of the lens

care procedures. On the other hand, the percentage of non-compliant subjects in

the current study decreased to 93% if we used the criteria in the study out carried

by Sokol et al. (1990), subjects were considered as non-compliant only if they

failed in three or more lens care procedures.

In the studies by Turner et al., (1993a &b) and Gower et al. (1994), subjects’

compliance were assessed according to the number of lens care procedures with

which they failed to comply. In addition, the non-compliant behaviour was

subjected to a weighting factor which the investigators developed to investigate

whether the non-compliant behaviour is clinically significant in relation to the safe

use of contact lenses.




                                                                             134
                                                                                           Chapter 7



Table 7.5.1 The percentage of non-compliant subjects and importance rating of
safety of each lens care procedure (Gower et al., 1994).


                                                       Percentage of     Importance Rating (Safety)*
                                                       non-compliant
                                                       subjects in the   Opti-     ReNu       AOSept
                                                        current study    Free
                                                           (before
                                                        intervention)
1. Wash hands with soap before handling
                                                             35%         7.25       7.58        7.77
   contact lenses
2. Clean contact lenses after lens removal                   35%         6.87       7.33        6.96
3. Rinse lenses with lens care solution
                                                             17%         6.79       5.79        6.32
   after cleaning
4. Fill lens case with adequate
                                                                 3%      6.04       6.62        5.64
    disinfecting solution as indicated
5. Rinse lenses with MPS/saline before
                                                             40%           /          /           /
    lens insertion
6. Disinfect contact lenses for time
                                                             12%         5.21       6.46        6.09
   recommended or longer
7. Redisinfect contact lenses, if they have
    been left in lens case for longer than                   73%         5.21         /         6.32
    indicated
8. Discard solution and air dry lens case
   after lens insertion                                      53%
a) Discard solution                                                      6.46       7.79        7.91
b) Air dry lens case                                                     5.37       6.21        4.86
9. Clean lens case with
                                                             65%         5.33       6.42        5.36
    MPS/cleaner/saline everyday
10. Disinfect lens case weekly                               87%           /          /           /
11. Change lens case every three months                      63%           /          /           /
12. Recap solution bottles every time
                                                                 0%        /          /           /
    after use
13. Check the expiry dates of lens care
                                                             58%           /          /           /
    solution regularly
14. Use MPS containing enzymatic
    cleaning agent or carry out enzymatic                    38%           /          /           /
    cleaning at least once a week
15. Change contact lenses regularly as
                                                             22%           /          /           /
    indicated
* Ratings ranged from 1= least important to 9 = most important




A summary of the percentages of non-compliance found in the current study,

together with the importance rating for safety used in the studies by Turner et al.

(1993a and 1993b) and Gower et al. (1994) are shown in Table 7.5.1. These

importance ratings for safety indicate the clinical significance of such

non-compliant behaviour with respect to safety in contact lens wear. Our results



                                                                                            135
                                                                            Chapter 7


indicate that at least one third of our subjects did not comply with lens care

procedures that are clinically significant with regard to safety in contact lens wear

which, according to Turner et al., (1993) should achieve an importance rating of at

least 6. Thirty-five percent of our subjects did not regularly wash their hands with

soap before handling contact lenses (importance rating 7.25 - 7.77); 35% did not

always clean their contact lenses after lens removal (importance rating 6.87 - 7.33);

and 53% did not discard their solutions and air dry their lens cases (importance

rating 4.86 - 7.91).



Among our subjects, most were non-compliant with up to seven lens care

procedures. Of the five different categories of lens care procedure, our subjects

had the worst level of compliance in accessories care. Aspects of lens care that

displayed the worst levels of compliance included questionnaire items:

7. Redisinfect contact lenses after they have been left in lens case for longer than

indicated (73% non-compliant).

8. Discard solution and air dry lens case after lens insertion (53% non-compliant).

9. Clean lens case with MPS/cleaner/saline everyday (65% non-compliant).

10. Disinfect lens case weekly (87% non-compliant).

11. Change lens case every three months (63% non-compliant).

13. Check expiry dates of lens care solutions regularly (58% non-compliant).




7.5.3 The effect of compliance enhancement strategy

At the end of the 12-month study, except for a few lens care procedures, there was

an increase in the percentage of compliant subjects (Section 7.4.3.1) and a

decrease in the contamination rates of lens cases and lens care solution (Section



                                                                             136
                                                                            Chapter 7


7.4.3.2). Our results indicate that the level of compliance of our subjects, both

Groups 1 and 2, improved throughout the study. The improvement in the level of

compliance of our subjects was probably due to the review of the lens care

procedures at the beginning of the longitudinal study and the regular aftercare

given to all of our subjects. Furthermore, there was an outbreak of severe acute

respiratory syndrome in Hong Kong during the period of our longitudinal study

(between March and June of 2003). Although this should not directly affect the

results of our compliance enhancement study, as no sample collections were

carried out within this period, all of our subjects may have become more alert

regarding their personal hygiene during this outbreak. This awareness may have

continued after the outbreak.

Self-review exercise was chosen as our compliance enhancement strategy because

it is simple to use, easy to deliver and not very time consuming. Moreover, it

allowed subjects to respond directly and helped to ensure that the enhancement

strategy was delivered to our subjects successfully. Our results have shown that

this enhancement exercise (self-review) had little effect on the level of compliance.

However, as the study relied on self-report of compliance, our results are subject to

recall bias. Subjects may either fail to admit poor compliance or be over-react of

their behaviour reporting themselves as non-compliant if failures are rare. Thus

there will be misclassification bias making the groups more similar to each other

and reducing the like hood to see a significant effect. Group 2 contact lens wearers

were found to be significantly more compliant in only one lens care procedure,

namely, number (9) cleaning lens case with MPS/cleaner/saline everyday, when

compared with Group 1.




                                                                             137
                                                                            Chapter 7


Wilson et al. (1990) compared the contamination of solutions and lens cases used

by contact lens wearers who received or did not receive reinforcement of lens care

instructions. They found a significantly lower contamination rate in the group of

contact lens wearers, who received reinforcement of manufacturer’s lens care

instructions. However, no such effect was observed in our study. This may be

because our subjects had a relatively lower contamination rate of their contact

lenses (6%) and contact lens accessories (15% to 40%). The results of our study

were similar to the results of the study carried by Claydon et al., (1997). They used

a similar method but a more complex enhancement strategy, which included video,

booklets, posters, checklist and a health care contract. At the end of their study,

they also found a slightly better compliance among subjects receiving a

compliance enhancement strategy, but there was no statistically significant

difference in the levels of compliance between the groups. The effect of the

enhancement strategy on levels of compliance and on contamination rates in our

study could also be limited by our sample size. We recommend larger subject

groups should be used in any future study of compliance.

Other reasons why our enhancement exercise did not show a statistically

significant effect on levels of compliance include the fact that one year may not be

long enough to show the difference between groups, and all of our subjects were

existing contact lens wearers. The failure of the intervention may be due to the

apparent/improvements of the control group as a result of the initial review as well

as the effect of being in a study, the “Hawthorne effect”. This change in behaviour

due to participation in a trial can make assessment of the intervention difficult.

Prolonging the length of a trial can overcome this as the effect of participation

declines. Non-compliance is related to the duration of the prescription (Claydon



                                                                             138
                                                                             Chapter 7


and Eforn, 1994) and contact lens care is a long-term preventative measure. Hence,

we believe that if we were to extend our study to a longer period, a stronger effect

of the compliance enhancement strategy would be shown. As mentioned earlier, it

is more difficult to increase the compliance of previous contact lens wearers, as

they tend to fall back into their old habits (Chun and Weissman et al., 1987). The

sensitivity of the study on compliance enhancement strategy could be increased, if

our subject group were formed of new contact lens wearers.



It has been suggested that a higher level of non-compliance with a care and

maintenance regimen may result in more contaminated lens cases (Wilson et al.,

1990; Mowrey-McKee et al., 1992). We found 73% of our subjects were

non-compliant with the care of lens cases, but there were only 40% (26/65) of our

subjects had contaminated lens cases. With the improvement in compliance of

lens care at the end of the study (from 73% to 66%), the contamination rate of lens

cases decreased by 10% (from 40% to 30%). The exact mechanism regarding the

influence of lens care compliance on the contamination of contact lenses and lens

care accessories is still unknown, but we believe the contamination of contact

lenses and lens care accessories is influenced by the level of compliance.



Although improving the compliance of contact lens wearers is seen to be difficult,

as primary eye care providers, we should promote lens care compliance more

strongly as an improvement in compliance will help in the prevention of

contamination of contact lenses and lens care accessories. Although it is relatively

easy to put the blame on patients for poor compliance, this can be avoided or at




                                                                             139
                                                                          Chapter 7


least reduced by proper training at the initial fitting of contact lenses and

reinforced at the follow-up visits.



7.6 Conclusion

Our study illustrates that all of the contact lens wearers showed some degree of

non-compliance in the care of their contact lenses and lens care accessories. Of 15

lens care procedures, most subjects were non-compliant with up to seven

procedures. The lens care procedures with the worst levels of compliance were

associated with care of lens case. Although our compliance enhancement strategy

did not significantly improve the level of compliance, mainly because compliance

improved in both groups of subjects, our results suggest that contamination of

contact lenses and lens care accessories is related to the level of compliance. The

contamination of contact lenses and lens care accessories was lowered with the

improvement in the level of compliance. Therefore, in order to lower the risk of

ocular complications induced by improper usage of contact lenses, regular review

of lens care procedures should be given to all contact lens wearers, no matter

whether they are existing or new contact lens wearers. Further studies with larger

samples and different population (non-student with different age and gender) are

required. In addition, changes to the design of the study may be necessary to

examine more fully the effects of compliance and non-compliance with contact

lens procedures.




                                                                           140
                                                                             Chapter 8




Chapter 8

Conclusion

8.1 The usage of contact lenses

Our results indicate that the usage of contact lens in Hong Kong is similar to that of

other countries. The increased popularity of PR contact lenses is likely to be part of

a global trend. Usage of rigid lenses has not increased over the past few years, and

the contact lens market in Hong Kong is driven by younger contact lens wearers.

The usage of over-night wear contact lenses (ortho-k and SH lenses) has been

limited by practitioners’ concern about safety. Practitioner’s felt that there is a

need to develop better speciality contact lenses with a wider range of parameters to

give better visual performance. Contact lens practitioners are also looking forward

to continuing education courses which could fulfil their requirements for updates

in contact lens practices.




8.2 Contamination of contact lenses

The use of contaminated contact lenses and lens care accessories by contact lens

wearers is not uncommon. From our results, around half of the contact lens

wearers were using contaminated contact lenses and lens care accessories.

Potential pathogenic microorganisms were frequently isolated from the test

samples, especially lens cases. Daily disposable/new/occasional wearers are at a

higher risk of having contaminated contact lenses or lens care accessories when



                                                                                  141
                                                                          Chapter 8


compared with experienced and regular contact lens wearers. Rinsing contact

lenses with either saline or MPS after cleaning is necessary to minimise contact

lens contamination. Our findings demonstrate that contact lenses, lens cases, and

lens care accessories were not well maintained by contact lens wearers.



8.3 The level of compliance and the effect of
    intervention on the level of compliance
Our results show that the spectrum of non-compliance is wide and every contact

lens wearers is a potential defaulter. All our subjects showed some degree of

non-compliance, and most subjects were non-compliant with up to seven (out of

15) lens care procedures; where some of these lens care procedures are clinically

significant with regard to safety in contact lens wear. Our compliance

enhancement strategy did not significantly improve the level of compliance,

mainly because compliance improved in both groups of subjects. The

contamination of contact lenses and lens care accessories was reduced with the

improvement in the level of compliance.




8.4     Further investigations

It is important for contact lens practitioners to keep up to date with the

developments in the contact lens practice in order to provide a high standard of

professional care to all contact lens wearers. Therefore regular and continue

monitoring of the usage and development of different contact lenses are important

and necessary.

Daily disposable/new/occasional wearers are at higher risk of having

contaminated contact lenses or lens care accessories. Further investigations with a


                                                                               142
                                                                          Chapter 8


larger sample size are needed to study contamination rates of contact lenses and

lens care accessories of contact lens wearing using different lens modalities.

Contact lenses and lens care accessories were found to be frequently contaminated

with potential pathogens. We suggest that further studies are performed to look for

new methods to protect contact lenses and lens care accessories from contaminants

such as stronger disinfecting solutions or bacterial-resistant contact lens or lens

case materials.

Although our compliance enhancement strategy did not significantly improve the

level of compliance, we believe this may due to our limited study period which did

not allow the effect of the strategy to be seen. Further study with larger samples,

better study design, and longer study periods are required. Different enhancement

strategies and different methodologies (e.g. observation method instead of

questionnaire) may also be useful to determine a more effective way to improve

compliance.




                                                                               143
                                                                                   Appendix I




                                      Appendix I

              A market survey of contact lens practice in Hong Kong

1.   What is the nature of your practice?
        Chain store                    Private Practice                Hospital
            Others (please specify)


2.   Under which part of registration are you registered in?
              Part I                     Part II                         Part IV


3.   How many people in your practice (include yourself) fit contact lenses?


4.   Indicate the percentage of your clients who are in each of the following category and
     the percentage of contact lens wearers in each category.
                                                                  Contact lens wearers
      Emmetropic                                            %                               %
      Hyperopic                                             %                               %
      Myopic                                                %                               %
      Total                                         100%


5.   Within the last 12 months, how many percent of your clients are new contact lens wea
     rers and how many are refits?
     New                                                    %
     Refits                                                 %
     TOTAL                                             100%


6.   On average, how many aftercare visits do you see your clients during their first year
     and second year of contact lens wear?
                                       1st year                         2nd year
     PMMA
     RGP
     Soft
     Orthokeratology



7.   How old are your youngest and eldest contact lens clients?

     Youngest                                      Eldest




                                                                                         144
                                                                                Appendix IV



8.    What percentage of your clients is prescribed with each of the following type of lenses?
      PMMA                                                                                   %
      RGP                                                                                    %
      Orthokeratology                                                                        %
      Soft                Conventional       Daily wear                                      %
                                             Extended wear                                   %
                          Disposable         Daily                                           %
                                             Biweekly                                        %
                                             Monthly                                         %
      Silicone hydrogel   (Pure Vision/      Daily wear                                      %
                          Night &Day)        Extended wear                                   %
                                             TOTAL                                      100%


9.    What is your recommended wearing schedule for the following types of lenses?
                                                                  Hours/Day Days/Week
      PMMA                                                               / 24        /7
      RGP                                                                / 24        /7
      Orthokeratology                                                    / 24        /7
      Soft               Conventional   Daily wear                       / 24        /7
                                        Extended wear                    / 24        /7
                         Disposable     Daily                            / 24        /7
                                        Biweekly                         / 24        /7
                                        Monthly                          / 24        /7
      Silicone hydrogel  (Pure Vision/  Daily wear                       / 24        /7
                         Night & Day)   Extended wear
                                        (Longest wearing                           Days
                                        schedule)


10.   On average, what percentage of your astigmatic clients (> -0.75D cyl) is prescribed
      with each of the following types of lenses?
      Spherical lenses
      Toric lenses
      TOTAL                                                            100 %


11.   Considering the existing disposable toric lenses available in the market, do you agree
      with the following phrases?
                                                                       Agree       Disagree
      Most of them provide stable and clear vision
      There are enough choices of back optical zone radius
      The range of spherical power are wide enough
      The range of cylindrical power are wide enough
      There are enough choices of axis




                                                                                         145
                                                                                 Appendix IV



12.   On average, what percentage of your presbyopic clients is prescribed with each of the
      following corrections?
      Monovision contact lenses                                                           %
      Bifocal contact lenses                                                                  %
      Multifocal contact lenses                                                               %
      Single vision contact lenses with over-spectacles                                       %
      TOTAL                                                                           100 %


13.   What percentage of your (asymptomatic) clients is prescribed with each of the
      following cleaning regimens?
      None                                                                        %
      Hydrogen Peroxide                 AOSEPT                                                %
                                        Oxysept B12                                           %
                                        Titmus                                                %
      Multipurpose Solutions            ReNu MultiPlus                                        %
                                        OPTI-FREE Express                                     %
                                        Complete                                              %
                                        Solo Care                                             %
      Others (please specify)                                                                 %
      TOTAL                                                                            100%


14.   Do you routinely advise your clients who use each of the following care regimens to
      rub their lenses during cleaning?
                                 Rubbing with     Rubbing without
                                                                           No rubbing
                                    cleaner           cleaner
      AOSEPT
      Oxysept B12
      Titmus
      ReNu MultiPlus
      OPTI-FREE Express
      Complete
      Solo Care


15.   How often do you advise your clients to carry out enzymatic cleaning?
                                                                                    Others
                                       Weekly       Biweekly   Monthly   Never      (please
                                                                                   specify)
      Conventional soft lens
      Biweekly disposable
      Monthly disposable
      Silicone hydrogel
      RGP/PMMA




                                                                                        146
                                                                                Appendix IV



16.   What are the most common complaints of your contact lens clients?
      (Please rank by putting in 1 to 6, with 1 - the most common complaint and 6 - the least
      common complaint)
              Dryness
              Tearing
              Foreign body sensation
              Blur/unstable vision
              Burning/Pain
              Redness
       Others (please specify)


17.   What percentage of your clients is prescribed with each of the following artificial
      tears?
      No artificial tear                                                                %
      Multi-dose                     Tears Naturale II                                     %
                                     Opti-Tear                                             %
                                     Senju                                                 %
                                     Hyoptears                                             %
                                     Renu Comfort Drop                                     %
                                     Refresh contacts                                      %
      Unit-dose                      Tears Naturale Free                                   %
                                     Hypotear Plus SDU                                     %
      Others (please specify)                                                              %
      TOTAL                                                                           100 %


18.   In your opinion, which of the following lenses have the highest potential for
      development in the contact lens market in Hong Kong? Are they available in your
      shop?
      (Please rank by putting in 1 to 6, with 1 - highest potential and 6 – least potential.)
       Market       Available in
       potential     your work
                       place
                                 Custom-make toric lenses
                                 Multifocal lenses
                                 Bifocal lenses
                                 Orthokeratology
                                 Silicone hydrogel (Daily wear)
                                 Silicone hydrogel (Extended wear)
       Others (please specify)




                                                                                        147
                                                                                    Appendix IV




19.    Where do you usually get new contact lens information?
       (Please rank by putting 1 to 5, with 1 - the most common source to 5 - the least
       common source.)
               Advertisements
               Colleagues
               Professional journals
               Contact lens suppliers/ Manufacturers
               Continuous education courses
        Others (please specify)




20.    Which of the following is/are helpful in increasing your sale of contact lenses?
       (Please rank by putting in 1 to 5, with 1 - the most helpful and 5 - the least helpful.)
               Advertising (e.g. TV, radio, road show)
               Free trial fit
               Package deals (e.g. buy 9 get 2 free)
               Extra gift (e.g. Towels)
               Special discount
        Others (please specify)




21.   If there is any other information that you think may be of use to this survey, please add
      your comments or suggestions below. You may also use this space for expanding on any
      of the areas of the questionnaire.




                                       ~        END      ~




                                                                                             148
                                                                 Appendix II




                             Appendix II

                     香港隱形眼鏡使用研究
1.   你工作的眼鏡店屬於以下那一種性質?
          連鎖店                      私營                     診所
          其他(請註明)



2.   你屬於哪一部份的註冊之中?
          第一部份                     第二部份                   第四部份



3.   在你工作的地方(包括你自己在內)總共有多少人從事驗配隱形眼鏡的工作? _________


4.   在你的客人當中需要不同視力矯正的分別有多少個百分比?他們當中有多少個百分比
     配戴隱形眼鏡?
                             當中配戴隱形眼鏡有
     平光                                   %                           %
     遠視                                   %                           %
     近視                                   %                           %
           總數                    100%




5.   在過去十二個月之中,經你驗配的客人分別有多少個百分比是隱形眼鏡的初次配戴者和
     重配人士?
     初次配戴者                                                %
     重配人士                                                 %
     總數                                    100%



6.   在初戴隱形眼鏡的第一年和第二年起,你的客人平均每年會作多少次覆檢檢查?
                                 第一年               第二年起
     硬鏡 PMMA
     透氣硬鏡 RGP
     軟性鏡片 Soft
     角膜矯視鏡 Ortho-K




7.   經你驗配的隱形眼鏡客人中最年輕及最年長的客人的年齡分別是多少?
     最年輕     _________________          最年長       _________________




                                                                          149
                                                              Appendix II



8.   配戴以下鏡種的客人的百分比分別是多少?
     硬鏡 PMMA                                                      %
     透氣硬鏡 RGP                                                     %
     角膜矯視鏡 Ortho-K                                                %
     軟性鏡片 傳統鏡                 日戴鏡                                 %
                              高透氧鏡                                %
               拋棄式            日戴鏡                                 %
                              兩星期鏡                                %
                              一個月拋棄鏡                              %
               超高透氧鏡          作日戴使用                               %
               (PureVision/
               Night & Day)
                              連續戴用模式                              %
                              總數                     100%



9.   你通常建議客人的佩戴時間是?
                                                   小時/天 天/星期
     硬鏡 PMMA                                        /24      /7
     透氣硬鏡 RGP                                       /24      /7
     角膜矯視鏡 Ortho-K                                  /24      /7
     軟性鏡片 傳統鏡                 日戴鏡                   /24      /7
                              高透氧鏡                  /24      /7
            拋棄式               日戴鏡                   /24      /7
                              兩星期鏡                  /24      /7
                              一個月拋棄鏡                /24      /7
            超高透氧鏡             用作日戴使用                /24      /7
            (PureVision/
            Night & Day)      連續戴用模式   最長連續佩戴多少天?                 天



10. 在有散光的客人中(散光>-0.75D)當中,平均有多少個百分比的客人會選擇佩戴近視鏡或
     散光鏡?
     近視鏡                                             %
     散光鏡                                             %
     總數                                     100%



11. 根據現時拋棄式散光鏡的市場,你會同意以下各項嗎?
                                                   同意       不同意
     大部份鏡片都能提供清晰及穩定的視力
     有足夠的弧度選擇
     有足夠的近視度數選擇
     有足夠的散光度數選擇
     有足夠的散光線位選擇




                                                                      150
                                                                           Appendix II




12. 在患有老花的客人中,平均有多少個百分比的客人會選擇以下的矯視方法?
    單光隱形眼鏡                         %
  雙光隱形眼鏡                                                               %
  漸進式隱形眼鏡                                                              %
  單光隱形眼鏡配合眼鏡一同使用                                                       %
  總數                                                           100 %


13. 你建議客人使用的以下隱形眼鏡藥水的百分比是?
  不使用任何隱形眼鏡藥水                                                    %
   雙氧水系列   AO Sept                                               %
                          Oxysept B12                            %
                          Titmus                                 %
   多工能藥水                  Renu MultiPlus                         %
                          Opti-Free Express                      %
                          Complete                               %
                          Solo Care                              %
   其他 (請註明)                                                      %
                                      總數               100%

14. 你建議客人使用的以下隱形眼鏡藥水的百分比是?

  不使用任何隱形眼鏡藥水                                                    %
  雙氧水系列    AO Sept                                               %
                          Oxysept                                %
                          Titmus                                 %
  多工能藥水                   Renu                                   %
                          Opti-Free                              %
                          Complete                               %
                          Solo Care                              %
  其他 (請註明)                                                       %
                                      總數               100%


15. 你通常建議佩戴以下鏡種的客人相隔多久才進行一次除蛋白程序?
                                           一星期   兩星期   一個月    不進行 其他(請註明)

   傳統性鏡片
   兩星期拋棄式
   一個月拋棄式
   超高透氧拋棄式
   (PureVision/ Night & Day)

   硬性鏡片 PMMA/RGP




                                                                                 151
                                                              Appendix II



16. 請將以下各項由佩戴隱形眼鏡最常見的投訴排列至最不常見的投訴。
    (請用 1 至 6 排列出來,以 1 為最常見,6 為最不常見。)
          眼乾
       流眼淚
       異物感
       視力模糊/不穩定
       刺痛感
       眼紅
       其他 (請註明)



17. 你建議客人使用人工淚液水/潤滑劑的百分比是?
    不使用任何人工淚水/潤滑劑                                         %
  支裝        淚然                                            %
            Opti-Tear                                     %
            目藥                                            %
            優樂沛                                           %
            Renu Comfort Drop                             %
            亮視                                            %
  獨立包裝      淚然 II                                         %
            優樂沛                                           %
  其他(請註明)                                                 %
  總數                                            100%




18. 你認為在現時的市場中以下那一種鏡最有市場發展的潛力?哪一種正在你們的
    店中出售? (請用 1 至 6 排列出來:以 1 為最有潛力,6 為最少潛力的鏡種。)
       預計市場             在店中有售
        潛力              的鏡片加
                                訂造散光隱形眼鏡
                                漸進式隱形眼鏡
                                雙光隱形眼鏡
                                角膜矯視鏡
                                超高透氧軟性鏡        (作日戴使用)
                                (PureVision/
                                Night & Day)   (連續戴用模式)
                                其他 (請註明)




                                                                    152
                                            Appendix II



19. 你通常從甚麼途徑中取得最新的隱形眼鏡資料?
    (請用 1 至 5 排列出來:以 1 為最常用,5 為最少用的途徑。)
           廣告
           同事
           專業期刊
           生產商/營業代表
           持續進收課程
           其他 (請註明)




20. 你認為以下哪一項最能幫助增加隱形眼鏡的銷售?
    (請用 1 至 5 排列出來:以 1 為最有幫助,5 為最少幫助的途徑。)


             廣告 (例:電視, 收音機, road show)
             免費試戴計劃
             套裝銷售 (例:買 9 送 2 優惠)
             贈品 (例:毛巾,眼鏡盒)
             折扣優惠
             其他 (請註明)




21. 如你認為有任何資料會對這項研究有幫助可利用此頁的空白地方發表你的意見如對以
   上的問卷有任何補充亦可在此提出。




                        ~     完     ~




                                                  153
                                                                                Appendix III




                                   Appendix III
         Research Study Information Sheet (For control group)

Title of Project:
Longitudinal Study of Contact Lens Care in Hong Kong and the Effect of
Interventions on Compliance.
Project Leader:
Dr. Pauline Cho, Rm. HJ539 (Tel:27666100)
Project Member:
Miss Alice Yung (Tel: 27664163)

Why is the study being performed?
This study aims to determine the level of compliance of contact lens wearers in Hong Kong
via a survey research and a microbiological study. Furthermore the effect of an intervention
on the level of compliance will also be studied.

What do volunteers for the study have to do?
1.   If you would like to volunteer yourself for the study, you will be asked to sign
     an informed consent form that states you understand the information
     presented on this sheet.
2.   You will be asked to come for 3 contact lens after-care visits. In each visit you
     will be provided a routine contact lens after- care consultation. You have to
     wear your current contact lenses, and bring along your contact lens case and
     contact lens solution (contact lens accessories). Swabbing samples will be
     taken from your contact lens surface and contact lens accessories.
3.   In the first visit, examiner will review contact lens cleaning procedures with
     you, and your old contact lens case will be replaced with a new one.
4.   In the first and last visit, you are required to complete a questionnaire.

Is there any benefit or risk if I participate in the study?
Benefits: You may not gain any personal benefits. The results however would be useful in
providing professional and ethical advice for contact lens wearing.
Risk: There is minimal risk as you will be examined by a professional optometrist, and all
the tests (except fluorescein instillation) are non-invasive. Very rarely, some patient may
react to the fluorescein dye but this will usually only cause some discomfort and corneal
staining which will do not harm to the patient and will disappear within a few hours.

Can a volunteer withdraw from the study?
You are free to quit this project at any time without any penalty.
Can I get more information on the study?
Yes, you can contact Miss Alice Yung/ Dr. Pauline Cho and she will try to answer any
questions you may have.

This study was approved by the Ethics Sub-Committee of The Hong Kong Polytechnic
University. However, if you think there are any procedures that seem to violate your welfare,
you may complain in writing to the Ethics Sub-Committee of the Hong Kong Polytechnic
University.




                                                                                        154
                                                                                 Appendix III




                                       Appendix III
             Research Study Information Sheet (For test group)

Title of Project:
Longitudinal Study of Contact Lens Care in Hong Kong and the Effect of
Interventions on Compliance.
Project Leader:
Dr. Pauline Cho, Rm. HJ539 (Tel:27666100)
Project Member:
Miss Alice Yung (Tel: 27664163)

Why is the study being performed?
This study aims to determine the level of compliance of contact lens wearers in Hong Kong
via a survey research and a microbiological study. Furthermore the effect of an intervention
on the level of compliance will also be studied.

What do volunteers for the study have to do?
1. If you would like to volunteer yourself for the study, you will be asked to sign
   an informed consent form that states you understand the information
   presented on this sheet.
2. You will be asked to come for 3 contact lens after-care visits. In each visit you
   will be provided a routine contact lens after- care consultation. You have to
   wear your current contact lenses, and bring along your contact lens case and
   contact lens solution (contact lens accessories). Swabbing samples will be
   taken from your contact lens surface and contact lens accessories.
3. In the first visit, examiner will review contact lens cleaning procedures with
   you, and your old contact lens case will be replaced with a new one.
4. In the first and last visit, you are required to complete a questionnaire.
5. Within the study period, you will receive a checklist of lens care reminder,
   which requires you to complete and return every 3 months.

Is there any benefit or risk if I participate in the study?
Benefits: You may not gain any personal benefits. The results however would be useful in
providing professional and ethical advice for contact lens wearing.
Risk: There is minimal risk as you will be examined by a professional optometrist, and all
the tests (except fluorescein instillation) are non-invasive. Very rarely, some patient may
react to the fluorescein dye but this will usually only cause some discomfort and corneal
staining which will do not harm to the patient and will disappear within a few hours.

Can a volunteer withdraw from the study?
You are free to quit this project at any time without any penalty.
Can I get more information on the study?
Yes, you can contact Miss Alice Yung/ Dr. Pauline Cho and she will try to answer any questions
you may have.

This study was approved by the Ethics Sub-Committee of The Hong Kong Polytechnic
University. However, if you think there are any procedures that seem to violate your welfare,
you may complain in writing to the Ethics Sub-Committee of the Hong Kong Polytechnic
University.




                                                                                         155
                                                                       Appendix III




                                Appendix III

      Longitudinal Study of Contact Lens Care in Hong Kong
           and the Effect of Interventions on Compliance.

Informed Consent Form

Have you read the information sheet provided?                           Yes / No

Have you had an opportunity to ask questions and discuss this study?    Yes / No

Have your received satisfactory answers to all of your questions?       Yes / No

Have you received enough information about the study?                   Yes / No

Who provided the information / answered your questions

Miss Alice Yung, OR, 27664163
Dr. Pauline Cho, OR, 2766 6100.


Do you understand that participation is entirely voluntary?             Yes / No

Do you understand that you are free to withdraw from the study

•   at any time                                                         Yes / No

•   without having to give a reason                                     Yes / No



Do you agree to take part in this study                                 Yes / No




Name: …………………………………………………………….




Signature: …………………………………                            Date: ………………………




                                                                              156
                                                                                  Appendix IV




                                    Appendix IV

Compliance Item 護理隱形眼鏡程序:

For the items below, please respond by circling the most appropriate number/answer.
請在以下各題填上你認為最適合的數字/答案。
  1 – Always 最常                                    2 – Often 時常
  3 – Sometimes 有時                                 4 – Seldom 很少時候

Cleaning 清潔程序:
  1. I wash my hands with soap before I handle my contact lenses.
      接觸鏡片前我會先用肥皂洗手
  2. I clean my contact lenses after lens removal.
      除下隱形眼鏡後我都會捽洗鏡片。
  3. I rinse my lenses with contact lens solution after cleaning.
      在清洗鏡片後我會用藥水沖洗隱形眼鏡。
Disinfecting 消毒過程:
  4. When I soak my contact lenses, I fill my contact lens case with
       adequate solution as indicated.
       在消毒時,我會依照指示把足夠的隱形眼鏡藥水注入鏡盒之內。
  5. I rinse my contact lenses with saline/multipurpose solution every time
       before lens insertion.
       在每次戴上隱形眼鏡前我會先用生理鹽水/多功能藥水沖洗鏡片。
  6. I disinfect my lenses with time longer than or as recommended.
      我都會用足夠的時間消毒鏡片。
  7. I redisinfect my contact lenses, if they have been left in lens case for
       longer than indicated.
      在不常戴隱形眼鏡的時候我會定期替鏡片消毒。
Accessories care 附件護理:
  8. I discard solution and let allow the case to be air dry after lenses are
      inserted.
      戴上鏡片後我會把鏡盒內的藥水倒出及讓鏡盒風乾。
  9. I clean my lens case with multipurpose solution/ cleaner with saline/
      disinfecting solution everyday.
      我每天都會用多功能藥水/清潔劑和盬水/消毒藥水清洗鏡盒一次。
  10. I disinfect my lens case weekly.
      我每星期都會替鏡片盒消毒。
  11. I change my lens case every 3 months.
      我每三個月便會更換鏡盒一次。
  12. I recap my solution bottle right after use.
      使用藥水後我會把瓶蓋蓋好。
  13. I always check the expiry dates of my contact lens solutions.
      在使用藥水時我常常會留意有限日期。
Enzymatic cleaning 除蛋白程序:
  14. I use multipurpose solutions containing enzymatic cleaning agent/               Yes 是/ No 否
       I carry out enzymatic cleaning at least once a week.
      我使用有除蛋白功能的藥水/我最少每星期進行一次除蛋白程序。
Replacement schedule 更換鏡片:
  15. I change my contact lenses regularly as indicated.
      我會在指定的日期內更換鏡片。




                                                                                          157
                                                                References


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