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Corneal refractive therapy _CRT_ An alternative method of vision

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Corneal refractive therapy _CRT_ An alternative method of vision Powered By Docstoc
					Clinical                                            Marc Brian Taub OD




    Corneal refractive therapy (CRT)
    An alternative method of vision correction
                                                                                                     Getting started
                                                                                                     The most important part of CRT, as with
     Whether your patients admit it or not, almost every single one of                               laser correction, is managing the patient.
     them has entertained the thought of not having to wear spectacles                               At our practice, we embrace the policy of
     or contact lenses. Thousands of patients around the world have                                  putting everything in writing as well as
     taken that step and have had refractive surgery – but a multitude of                            verbally explaining the process, results and
     patients have not. There are various reasons why so many potential                              costs. When selecting patients, refractive
     refractive surgery candidates have not made that commitment –                                   error is as important as personality. If the
     cost, refractive stability, or fear of surgery – take your pick. There                          patient’s or even worse, the patient’s
     is and has been an alternative for almost 40 years – corneal                                    parents’ expectations are too high, you are
     refractive therapy (CRT), otherwise known as orthokeratology.                                   primed for failure. Take your time and
                                                                                                     explain what they can expect and the
                                                                                                     limitations of the process. We try to
    History                                         return zone, the landing zone and the edge       emphasise that CRT is a process which will
    The idea of flattening the cornea to reduce     terminus (Figure 1). The central base curve      take time and that results can vary from
    refractive error dates back many centuries      is the ‘workhorse’ of the design, providing      patient to patient.
    to China. Sandbags were laid on closed          the ‘mould’ by which the corneal changes             Who is a good candidate? The FDA has
    eyes, creating pressure on the cornea which     can occur. This curve is selected flatter than   approved corneal refractive therapy for
    improved vision. Earlier in the 20th            the cornea and will guide the reduction in       patients with refractive errors between
    century, a device which claimed to improve      refractive error. The second element is a        -0.50D and -6.00D, and up to -1.75 of
    myopia was available via mail order.            sigmoid-shaped curve which allows the            astigmatism10. Beginners should concentrate
    It essentially provided a quick jolt of         lens to have consistent and closer contact       on patients with little to no astigmatism
    pressure on the closed eye causing the          with the cornea as the changes are taking        and myopia between -2.00D to -4.00D. As
    cornea to flatten temporarily1.                 place. This element or zone is known as the      your experience with CRT grows, you can
        More recently, in the 1960s, the idea of    return zone. The third element, the landing      then begin to take on more difficult cases.
    flattening the cornea using contact lenses      zone, is concentric to the return zone and       Myopes as young as eight years of age can
    came to life. In 1962, Jessen reported to the   tangential to the cornea. The fluid forces       benefit since the procedure can slow or
    International Society of Contact Lens           arising from the ‘approximation’ of the          stop the progression of myopia9. Current
    Specialists on his “orthofocus techniques”      landing zone and the cornea, as well as          and previous hard and soft contact wearers,
    to deliberately change the shape of the         other factors, provide stabilisation to the      as well as patients who have never used any
    cornea2-5. Others, such as Grant and May,       lens on the eye. The edge terminus, the          contact lenses, can undergo CRT. Contact
    and Tabb have tried various approaches          most peripheral element, promotes the            lens wearers could have an advantage since
    using lenses flatter than the flattest          comfort of this lens design. It curves away      they understand lens cleaning and insertion
    K-reading and constantly flattening the lens    from the cornea to merge with the anterior       and removal at a basic level. Presbyopes
    as the cornea changed2-4. These techniques      surface forming the edge of the lens7,8. The     need not be excluded from CRT. It must be
    were both unpredictable, often causing          material of the lens is fluorosilicone           explained that just as with refractive
    significant amounts of astigmatism, and         acrylate copolymer with a water content of       surgery, presbyopes will have to use near
    time-consuming1,4,5. The lenses used were       less than 1% and a Dk of 1008.                   vision spectacles when attempting to read
    PMMA lenses, which also caused some                 The Paragon CRT lens does not simply         or use the computer. Another option for
    corneal oedema5.                                press on the cornea to cause flattening; the     presbyopes is monovision. While not an
        The modern orthokeratology lens is          lens is fitted such that a tear reservoir is     option for all patients, some, especially
    based on the ‘reverse geometry’ lens            created. The secondary curve, which is           those wearing monovision contact lenses,
    designed by Stoyan, using a three zone          steeper than the central curve, creates a        may benefit from this type of correction9.
    system5. These lenses have a secondary          positive pressure on the central cornea and          The contraindications to the use of the
    curve that is steeper than the base curve.      a negative pressure in the tear reservoir        Paragon CRT lenses are the same as with
    This improvement led to better lens             area9. This will cause a redistribution of       any conventional RGP lens. Moderate to
    centration and the presence of a tear           epithelial tissue peripherally, essentially      severe dry eyes, reduced corneal sensitivity
    reservoir, which increased the efficacy and     flattening the central cornea7. Most             and any inflammation or infection of the
    speed of the procedure6. While this new         importantly, a lens which fits well should       anterior segment eliminates a potential
    design was an improvement, centration           have little or no central touch6.                candidate. A patient who has an eye
    and, therefore, predictability remained an                                                       disease, injury or abnormality which affects
    issue. The next improvement in lens design                                                       the cornea, conjunctiva, or eyelids, or has a
    was the four zone design, made by El Hage                                                        systemic disease which might affect the eye
    and Reim. This design led to better control                                           Figure 1   or be exacerbated by using CRT lenses,
    of the changes that were occurring and                                Paragon CRT lens design    should be disqualified. Of course, anyone
    better outcomes5.                                                                                who develops a corneal infection or who
                                                                                                     has an allergic reaction to the lens material
    Lens design                                                                                      or solution during the process should
    The Paragon CRT lens, which has recently                                                         discontinue immediately.
    received FDA approval in the United States                                                           Most of the information you need for
    for night-time use, consists of four                                                             fitting CRT lenses can be collected during a
    elements – the central base curve, the                                                           routine eye examination. Most importantly,


      28 | May 16 | 2003 OT
                                                                                                                                    Clinical




an up-to-date refraction should be                absent treatment zone would result if the         proper fit. Visual acuity as well as an over-
performed and keratometry readings                sagittal depth was too deep. A decentred          refraction is performed both with and
taken. If a patient uses hard lenses, instruct    lens can lead to corneal changes, which can       without the lenses in place. Most
them to discontinue lens use for several          affect the visual outcome. Minimal edge lift      importantly, a corneal topography should
days prior to the examination to get the          or a tight periphery is also a problem for        be taken.
most accurate readings. The K-readings can        long-term success. If the initial lens does           As previously stated, the most important
be gleaned from either an autorefraction or       not fit properly, alterations must be made        method for evaluating the fit of the
corneal topography.                               prior to dispensing. Changes can be made          overnight CRT lens is corneal topography.
   While corneal topography is not needed         to the base curve, RZD or LZA.                    Figures 7a and 7c compare a pre-fit and
for the initial fitting, it is absolutely             The RZD is adjusted in steps of               post-fit topography with a well-centred
necessary to truly evaluate the fit of lenses     0.025mm, which is equal to 25 microns,            lens. This is often referred to as a Bull’s Eye
and to make changes in lens design to             while the LZA can be altered in one or two        pattern. You can see the central corneal
maximise the refractive error changes.            step increments. The base curve should be         flattening as well as the mid-peripheral
Topography allows for pre-fitting screening       changed if under-treatment is an issue after      steepening13. Studies have shown that the
for pathologic corneas and establishes the        the first two weeks of treatment. Most            maximum unaided visual improvement is
baseline shape of the cornea11. While you         changes should wait that two-week                 made within one week14, 15, so changes must
can view the lenses on the patient’s eye in       ‘purgatory’ period unless there are obvious       be made immediately to ensure success. If
your examination chair and even evaluate          fitting problems or the cornea is                 an improperly fitting lens is left on the eye
them after overnight wear, only topography        compromised12.                                    for too long, it will become increasingly
provides information on contraction                   After the proper lens has been chosen,        difficult to alter the cornea with a different
vertically and horizontally.                      the patient must be taught to insert and          lens.
                                                  remove the lens as well as about the care             In contrast, when the lens is not well
Fitting the lens                                  regime, both of which may be different            centred, the topography will appear
The initial lens choice is based on the           than they are used to with their soft lenses.     different depending upon the lens position
refractive error and the keratometry              We teach the patient to remove the lens           at night. If the lens is riding too low, a
readings. The flat K and the amount               with a DMV and to place a drop of artificial      ‘frowny face’ pattern will appear (Figure 3).
of myopia are cross-referenced on the             tears in prior to removal. This will keep the     This would represent a lens that is slightly
Paragon CRT Initial Lens Selector. This           lens from roughening the cornea. The              too steep. The superiorly riding lens would
chart provides a set of three numbers for         solution which we recommend patients use          create a ‘smiley face’ pattern (Figure 4).
your lens – the base curve (BC), the return       in conjunction with the Paragon CRT lenses        This pattern would result from a flat fitting
zone depth (RZD) and the landing zone             is Unique pH Multi-Purpose. The patient is        lens11. The lens can also be decentred
angle (LZA). That lens is placed on the eye       instructed to clean the lens with the             laterally or a combination of both vertical
during the in-practice fitting. It is best to     Unique pH and to also use one drop of             and horizontal (Figure 5). A ‘central
use a drop of anaesthetic prior to placing        Supraclens in each well nightly.                  islands’ pattern, or one in which there are
the first lens on the eye.                            The morning after the fit, the patient        untreated areas located below the retainer
    There are several factors to evaluate,        returns wearing the lens. Another                 lens, can result from a lens with a sag that
both on the initial fit as well as throughout     evaluation of the fit is made using               is too deep8 (Figure 7d).
the process. A properly fitting lens shows a      fluorescein and a Burton lamp or slit lamp.           After the patient returns to the practice
‘black, green, black, green’ pooling pattern      If some staining of the central cornea is         the next morning, you should plan to see
(Figure 2). The borders of these zones            present, advise the patient to instil two         them again within the first week. If a
should be distinct and not smudged. The           drops of artificial tears both before going to    change in lens parameters was made, see
lens should be centred on the pupil and           sleep and in the morning prior to lens            the patient in three to four days. If no
limbus-to-limbus. The treatment zone in           removal. Permanent staining indicates that        change is made, a week will suffice. Since
the centre of the lens should measure at          mechanical irritation or some defect in the       the corneal changes are occurring gradually,
least 4mm. The edge lift must be                  corneal physiology is creating a problem5.        the patient should be prepared to re-insert
acceptable. Use the Goldilocks approach in        Changes might be needed to ensure a               the Paragon CRT lenses as daily wear and
this case, i.e. not too much, not too little,
but just right.
    On the other side of the spectrum, the
lens can also be unacceptable. A small or                                                                                                   Figure 3
                                                                       This topography indicates a ‘frowny face’ pattern or an inferiorly riding lens


                                      Figure 2
      This lens provides acceptable centration,
                  treatment zone and edge lift




                                                                                                                        29 | May 16 | 2003 OT
Clinical                                            Marc Brian Taub OD




                       Figure 4 This topography indicates a ‘smiley face’                                 Figure 5 This topography shows a pattern
                                      pattern or a superiorly riding lens                                             indicative of a decentred lens

   as necessary for good vision throughout the     period.                                           increases. A patient who has 2.00D of
   initial treatment period. Remember,                 Some may use temporary soft contact           myopia probably will not complain much
   patients can always see perfectly through       lenses during the day. This circumstance          of some fuzziness beyond the first day, but
   the Paragon CRT lenses throughout this          arises as the refractive error being corrected    someone who has 3.50D and above might
                                                                                                     need at least a night time lens for the first
                                                                                                     week until the new shape takes hold. For
                                                                                                     example, a 4.00D myope is given a -1.50D
                                                                                                     for day time use the first few days and a -
                                                                                                     2.50D to 3.00D for the night for the same
                                                                                                     time frame. At the next follow-up visit, that
                                                                                                     daytime lens becomes the night-time lens.
                                                                                                     This slight blur, especially at night, may
                                                                                                     take several weeks to abide.
                                                                                                         Keeping in mind that every individual
                                                                                                     will have a slightly different CRT
                                                                                                     experience, a general schedule for
                                                                                                     follow-up visits is similar to one after
                                                                                                     cataract surgery. You see the patient the
                                                                                         Figure 6    next day, at one week, one month, three
                                                      Case one – three-month post-fit topography     months, six months and then for their
                                                                                                     yearly visit. Once the patients vision has
                                                                                                     become stable throughout the day and
                                                                                                     does not seem to fade at night, I advise the
                                                                                                     patient to experiment with leaving the lens
                                                                                                     off one night to check the stability into the
                                                                                                     next day. This usually takes place at around
                                                                                                     the one-month visit.
                                                                                                         A spare pair of CRT lenses should be
                                                                                                     part of your CRT plan. Once the vision is
                                                                                                     stable and you are positive the lenses will
                                                                                                     not be changed, issue the spare pair. With
                                                                                                     discontinued lens use (for any reason), the
                                                                                                     visual and refractive data will regress
                                                                                                     toward baseline levels at a rate of about
                                                                                 Figure 7 a and b    0.50D to 0.75D per day15. With all of your
                                                                     Case two – pre-fit topography   hard work to attain changes in the cornea,
                                                                                                     you do not want to see it lost.
                                                                                                         Once you get started with CRT, you will
                                                                                                     realise that it is not as complicated as it
                                                                                                     might initially appear. We are so lucky to
                                                                                                     practise in a time when there are so many
                                                                                                     choices in vision correction. Spectacles,
                                                                                                     contact lenses, laser vision correction, and
                                                                                                     now CRT provide patients with so many
                                                                                                     options. While there are so many other eye
                                                                                                     professionals prescribing spectacles, fitting
                                                                                                     contact lenses and co-managing refractive
                                                                                                     surgery, dare to be different. With this new
                                                                                                     easy-to-fit, easy-to-predict and easy-to-use
                            Figure 7c and d Case two – two and a half month post-fit topography;     corneal refractive therapy lens system, this
                         Figure 7d shows central island represented by an area of under treatment    is your chance.


      30 | May 16 | 2003 OT
                                                                                                                               Clinical




                      RE/LE      Unaided VA    Refraction              Keratometry                References
                                                                                                  1. Tabb R (2000) Overnight
     Dispensing         RE            NA       -3.00-0.50 x 085        44.75/45.00@125                orthokeratology. Contact Lens Spectrum
                        LE            NA       -3.00-0.75 x 102        44.50/45.25@123                15; 10: 22-25.
                                                                                                  2. Coon L (1982) Orthokeratology
        One day         RE           6/12      -0.50-0.25 x 090                                       historical perspective: Part I. Journal of
                        LE           6/30      -1.25-0.50 x 110                                       the American Optometric Association
                                                                                                      53 (3): 187-195.
       One week         RE          6/7.5-     +0.50-0.75 x 080                                   3. Carkeet N, Mountford J and Carney L
                        LE           6/9-      PL -0.75 x 090                                         (1995) Predicting success with
                                                                                                      orthokeratology lens wear: a
    Three weeks         RE           6/6-      No improvement                                         retrospective analysis of ocular
                        LE           6/9+      PL -0.75 x 095                                         characteristics. Optometry and Vision
                                                                                                      Science 72 (12): 892-898.
    Three and a         RE           6/6-      No improvement                                     4. Dave T and Ruston D (1998) Current
    half months         LE           6/6-      No improvement                                         trends in modern orthokeratology,
                                                                                                      Ophthal. Physiol. Opt. 18 (2): 224-233.
                                                                                                  5. Polymer Technology Corporation
  Table 1 Vision correction for case one                                                              (2002) A guide to overnight
Case one                                                   Case two                                   orthokeratology.
Carmen was a lifelong contact lens wearer                  Jonathan came into our practice        6. Bauman R (2001) Getting started with
who complained of some dryness when using                  for a LASIK screening. After the           accelerated ortho-K. Optometric
her two-week disposable lenses. Her anterior               screening was completed and the            Management 36; 5.
segment, including the cornea, was healthy                 surgery scheduled, the patient got     7. Caroline P (2002) What makes CRT
showing a slight amount of neovascularisation              cold feet. He jumped at the                different. Contact Lens Spectrum 17;
inferiorly in both eyes. The original lenses               chance to undergo CRT. He was              9 (Suppl): 10-13.
selected were 8.3 BC, 550 RZD, 33 LZA for                  fitted with 8.3 BC, 550 RZD,           8. Paragon Vision Sciences (2002).
both eyes. These lenses were well centred, and             34 LZA OD, 8.1 BC 550 RZD,                 Dispensing set guide.
showed the typical ‘black, green, black, green’            34 LZA. The lenses were dispensed      9. West W (2002) Integrating CRT into
pattern. The lenses were dispensed to the                  and fitted well the next morning.          your practice. Contact Lens Spectrum
patient.                                                   The patient was given two pairs of         17; 9 (Suppl): 4-7.
   The appearance of the lenses after one                  disposable soft lenses, for            10. Bauman R (2001) A Night and day
night of use was different than seen the                   temporary use during the day               difference Part 1. Optometric
previous day. The lens appeared ‘sucked’ onto              (-1.00D) and night (-2.00D) until          Management 36; 4.
the eye. They were removed, reinserted and                 the changes were more permanent        11. Mountford J, Caroline P and Noack D
then appeared sealed off temporally. The LZA               (Table 2). The baseline                    (2002) Corneal topography and
was lowered to 32 in both eyes and the left                topography can be contrasted               orthokeratology: pre-fitting
lens BC was flattened to 8.4. This produced                with the two and a half month              evaluation. Contact Lens Spectrum
the expected pattern for a well fitting lens. As           topography (Figures 7 a to d).             17; 4.
shown in Table 1, the vision correction                    You can see the central flattening     12. Jackson J and Rah M (2002) Managing
peaked at around one week and continued to                 with the mid-peripheral                    CRT challenges. Contact Lens Spectrum
improve. Soft disposable lenses of powers                  steepening on the right eye                17; 9 (Suppl): 14-15.
-2.00D and -1.00D were dispensed for the first             topography. While the topography       13. Mountford J and Noack D (2002)
few days for night-time and daytime use                    on the left eye shows central              Corneal topography and
respectively. The weaker lenses were then                  islands, the vision is acceptable to       orthokeratlogy: post fit assessment.
switched to only night-time use after several              the patient. In this case, I chose         Contact Lens Spectrum 17; 6.
days. The vision is now stable and the lens is             not to alter the parameters of the     14. News (2002) Ortho-K eyes peak in
worn every third night. The topography seen                lens. If further flattening was            one week. Review of Optometry 139;
here was taken at the three-month visit                    indicated by poor vision, the base         1: 10.
(Figure 6). While not perfect, the patient’s               curve would be flattened and the       15. Nichols J, Marsich M, Nguyen M, Barr
success dictates the process.                              LZA decreased.                             J and Bullimore M (2000) Overnight
                                                                                                      orthokeratology. Optometry and Vision
                                                                                                      Science 77 (5): 252-259.
  Table 2 Vision correction for case two
                                                                                                  About the author
                    RE/LE      Unaided VA     Refraction             Keratometry                  Marc Taub is in private practice
                                                                                                  at Rummel Eye Care in Jackson,
    Dispensing        RE            NA        -3.50 sph              45.00/46.00@160              New Jersey, USA. He begins a
                      LE            NA        -3.00-0.50 x 068       45.50/46.25@133              paediatric residency at Nova
                                                                                                  Southeastern University in South
       One day        RE            6/6       -0.25 sph                                           Florida in July.
                      LE            6/9       -0.75-1.00 x 075

     One week


    Two and a
   half months
                      RE
                      LE

                      RE
                      LE
                                    6/6+
                                    6/6+

                                    6/6
                                    6/6-
                                              No improvement
                                              No improvement

                                              No improvement
                                              No improvement
                                                                                                       ot
                                                                                                        www.optometry.co.uk


                                                                                                                   31 | May 16 | 2003 OT

				
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