Refractive Surgery – Presbyopic LASIK and Multifocal Intra-Ocular

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Refractive Surgery – Presbyopic LASIK and Multifocal Intra-Ocular Powered By Docstoc
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               MODULE 11 PART 10                                                                                                                                           COURSE CODE: C-8162



                 Refractive Surgery – Presbyopic
 30
                 LASIK and Multifocal Intra-Ocular
                 Lenses
 3/10/08 CET




                                                                                  Professor Dan Reinstein MD MA(Cantab) FRCSC FRCOphth
                                                             Presbyopia is the loss of the ability for the eye to accommodate or change focus
                                                             from viewing a distant object to viewing an object up close. This loss of
                                                             functionality is due to a gradual loss of amplitude of accommodation that is
                                                             provided by the crystalline lens. The loss of accommodation is a slow
                                                             progressive process that begins from birth. At age 8, the average amplitude of
                                                             accommodation is 14.00 to 16.00 diopters (D); it declines to 10.00 ± 2.0 D by
                                                             age 25, to 6.00 ± 2.00 D by age 40, and to 1.00 D ± 1.00 D by age 60 (Figure 1).1,2
                                                             However, the effect of accommodation loss is only felt from the age of
                                                             approximately 45 as it is at this stage when the residual focusing power of the
                                                             crystalline lens cannot provide sufficient near vision. A person unable to
                 maintain 3.00 D of accommodation for any length of time is considered to have symptoms of presbyopia. Presbyopia
                 occurs in 100% of the population and as longevity increases, presbyopes now represent one of the largest groups of
                 patients suffering from a refractive error.


               The ideal solution to correcting                                 Non-surgical solutions:                                                            spectacles.5 This effect is more
               presbyopia would be to restore                                   Spectacles                                                                         pronounced with high prescriptions,
               accommodation,        however,      no                           Traditional non-surgical methods of                                                particularly for high astigmatism and
               procedure up to now has been proven                              refractive correction for presbyopia                                               so a proportion of patients are unable to
               to reverse presbyopia and restore the                            include the use of dedicated reading                                               adapt to this mode of correction.
               natural focusing mechanism of the                                spectacles, bifocal, or varifocal
               eye. Although there is ongoing                                   spectacles, monovision contact lenses                                              Non-surgical solutions:
               research on techniques to achieve this,                          or multi-focal contact lenses. Studies                                             Monovision contact lenses
               clinical    applications    of   these                           have indicated that multi-focal                                                    The most widely used non-spectacle
               techniques will probably not be                                  spectacles impair depth perception                                                 method of presbyopia correction is the
               available for another 10 to 20 years.3                           and edge-contrast sensitivity at                                                   use of contact lenses through the
               As it is not possible to restore                                 critical distances for detecting                                                   application of monovision. In this
               accommodation, current treatments                                obstacles in the environment.4 While                                               technique, the eyes are dissociated by
               focus on compensating for the lack of                            in varifocal lenses, there is a corridor                                           focusing one eye for distance vision
               accommodation by providing a                                     of continuously changing lens power                                                and one eye for near vision (see Figure
               different refractive power at distance                           and optimal vision is only obtained                                                2). However, the large image disparity
               and near. The challenge of such                                  when looking though this corridor                                                  between the two eyes causes several
               treatment options is to provide both                             and directly facing the object of focus.                                           limitations to the quality of overall
               distance and near vision while                                   Outside this corridor, the vision is                                               vision. Although binocular distance
               simultaneously maintaining optical                               distorted and peripheral vision is                                                 visual acuity remains optimal with
               quality, with particular regard to                               reduced. For these reasons, older                                                  monovision contact lenses, subjective
               contrast sensitivity and night vision                            people are more than twice as likely                                               quality of vision is decreased. There is
               preservation.                                                    to fall when wearing multi-focal                                                   no change in distance visual acuity

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        because the dominant eye is able to                       refractive surgery. Traditionally, the        reversing the procedure and the
        suppress the blurred image from the                       principles used for monovision contact        increased time for adaptation. Early
        near vision eye to provide good                           lenses have been applied to corneal           outcomes for monovision induced by
        binocular vision. However, the loss of                    refractive surgery using Laser in-situ        refractive surgery show that 76% of
        fusion between the two eyes affects                       Keratomileusis (LASIK) or Photo               patients could read 6/6 at distance and
        subjective quality of vision and                          Refractive      Keratectomy         (PRK)     95% of patients could read N5 at near.12
        patients can complain of halos, glare,                    techniques. In LASIK, either a                The goal of monovision is to increase
        haze and starburst. The severity of                       microkeratome or a femtosecond laser          functional vision without the aid of
        these symptoms increases with                             is used to create a flap; the flap is then    eyeglasses for the majority of everyday
        increasing power difference between                       lifted and an excimer laser is used to        tasks. However, distance or near               31
        the distance eye and the near eye; the                    reshape the cornea. PRK is a surface          spectacle correction may be prescribed
                                            6
        older, the more difference required.                      ablation where no corneal flap is             for certain specialised tasks requiring




                                                                                                                                                               3/10/08 CET
          Further, as one eye is focused for                      created; instead, the epithelium is           either good binocular distance vision
        near and the fellow eye for distance                      removed, and the excimer laser is used        (ie, night driving) or good binocular
        vision,    another     limitation     of                  to reshape the cornea.                        near vision (ie, prolonged reading).
        monovision is the gap in the range of                        As with contact lenses, the dominant          Recently, with the advances made in
        clear vision at intermediate distance7                    eye is focused for distance vision and        laser eye surgery, experimental
        (computer, TV). Reduced stereopsis is                     the non-dominant eye for near vision.         approaches have been used to create a
        considered to be the major limitation                     However, many of the same limitations         number of different multi-focal ablation
        to monovision correction; both                            are found with monovision contact             profiles. “PresbyLASIK”, also called
        distance and near stereopsis have been                    lenses applied to monovision induced          “multifocal PresbyLASIK”, groups a
        shown to decrease while wearing                           by refractive surgery, including loss of      series of corneal surgical techniques
        monovision correction.6,8 Binocular                       fusion and stereoacuity.10 Fawcett            based on the principles of LASIK to
        contrast sensitivity has also been                        demonstrated that the reduced                 create a multifocal corneal surface
        shown to decrease with progressive                        stereoacuity due to longstanding              aimed to reduce near vision spectacle
        increase in contact lens power in the                     anisometropic blur induced by                 dependence in presbyopic patients.
        near eye.9 The combination of these                       monovision correction cannot be               Essentially, it is a corneal refractive
        limitations means that monovision                         immediately corrected by providing            surgery      technique     that   creates
        correction can only be tolerated by up                    full       binocular         correction.10    discontinuous optics and more than one
        to 60% of patients.7                                      Interestingly, monovision induced by          focal plane. In such techniques, either a
                                                                  refractive surgery can be tolerated by a      central corneal area is steepened for
        Surgical solutions: Excimer                               higher proportion of patients (92%)           near vision leaving the mid-peripheral
        laser treatments                                          than monovision induced by contact            cornea for far vision (central
        One surgical method of refractive                         lenses.11 It is unclear whether this          presbyLASIK) or a central area for
        correction for presbyopia is laser                        might be due to the difficulty of             distance vision is created with a mid-
                                                                                                                peripheral corneal area for near vision
                                                                                                                (peripheral presbyLASIK). For example,
                                            Amplitude of Accomodation with Age                                  for a central near vision treatment and a
                                                                                                                typical 6.00mm optical zone, the
                                                                                 Donders        Duane           distance correction is applied over the
                                                                                                                entire 6.00mm zone but the central
                                                                                                                3.00mm of the treatment zone is
         Accommodation of Amplitude (D)




                                                                                                                purposely rendered hyperpositive by an
                                                                                                                additional 1.50 D. The rationale here is
                                                                                                                that as the pupil constricts during the
                                                                                                                accommodative effort of looking at near,
                                                                                                                the central corneal ‘add’ will kick-in. A
                                                                                                                1.50mm circumferential transition zone
                                                                                                                of gradually changing power connects
                                                                                                                the portion of the cornea corrected for
                                                                                                                distance with the region corrected for
                                                                                                                near. One of the limitations of this is
                                                                                                                that pupil size varies between
                                                                                                                individuals, with many possessing a
                                                                                                                smaller pupil size even at distance gaze.
                                                             Age/years                                          More work is needed in the multifocal-
                                                                                                                cornea domain to overcome these pupil
       < Figure 1                                                                                               size issues.
         The decline of amplitude of accommodation with age1,2                                                     Nevertheless, while an overall
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                                                                                                                   operative visit to -1.06 D at the three-
                                                        ¤ Dominant eye:
                                                                                                                   year post-operative visit. While 100%
                                                        Focused for distance, blurred at near
                                                                                                                   of patients maintained distance
                                                                                                                   binocular UCVA of 6/6 (the distance
                                                                                                                   eye was untouched), 78% of patients
                                                                   ~60%                                            could read N6 or better at near.16 In
                                                                   Patients Tolerate                               addition,      surgically      induced
                                                                                                                   astigmatism compromises visual
                                                                                                                   results. McDonald reported that 27%
 32                                                                                                                of eyes had a change in cylinder
                                                                                                                   between 1.00 D and 2.00 D at one
                                                                                                                   month and 8% of eyes at six months
 3/10/08 CET




                                                                                                                   post-operatively.17 The usefulness of
                                                                                                                   CK is therefore limited because it can
                                                                                                                   only be used to treat plano presbyopic
                                                                                                                   patients and regression appears to be
                                                                                                                   common and eventually, complete.
                                                                   2 Brain merges two images to see near and far
                                                                   without spectacles                              Surgical  solutions: Intra-
                                                                                                                   Ocular Lens Implantation
               2 Non-dominant eye: Focused for near,                                                               In addition to laser techniques, a
               blurred at distance                                                                                 popular     method      of   correcting
                                                                                                                   presbyopia is to perform intra-ocular
                                                                                                                   surgery, removing the patient’s
               < Figure 2
                                                                                                                   crystalline lens and replacing it with
                 Monovision: Brain splitting. Monovision correction adjusts each eye separately for distance and   an intra-ocular lens (IOL). Standard
                 near vision. There is a gap at intermediate.
                                                                                                                   IOLs are monofocal, aiming to provide
                                                                                                                   the patient with clear focused distance
               improvement in visual acuity has been               overcorrection and have shown                   vision and the need for spectacles for
               recorded for both near and distance                 significant regression. One year results        clear near vision. Multi-focal IOLs
               vision with multifocal corneal LASIK,               for the treatment of low to moderate            comprise multiple focal lengths
               safety and quality of vision have been              hyperopia demonstrated that, at one             within the optical zone while
               compromised.13 It has been reported                 year, 56% of eyes had a distance UCVA           accommodating IOLs18 use movement
               that 20% of eyes lost two lines of best             of 6/6 or better, and 63% of eyes were          of the IOL, both with the intention of
               spectacle corrected visual acuity                   within ± 0.50 D of the intended                 providing good unaided distance and
               (BSCVA) at distance and 52% of eyes                 refraction.14 The mean manifest                 near visual acuities.
               lost two lines of BSCVA at near, while              spherical equivalent (MRSE) changed
               only 48% of eyes achieved 6/6                       from -0.52 D at one month to +0.22 D at         Multifocal Intra-Ocular
               uncorrected visual acuity (UCVA).13                 12 months. Ehrlich15 demonstrated               Lenses
               Further, by creating discontinuous                  complete regression of the effect in all        There are two main types of multifocal
               optics between the central and the mid-             of 25 mild to moderate hyperopes over           IOLs: refractive IOLs and diffractive
               peripheral cornea, contrast sensitivity             the long-term after CK treatment; the           IOLs; each type comprising different
               was decreased and 12% of patients                   mean MRSE in their study was +1.47 D            optical designs. Both these lenses use
               reported night vision disturbances.                 pre-operatively, +0.36 D at 12 months,          the same principle of simultaneous
                                                                   +0.57 D at 24 months and +1.39 D at 73          vision and aim to correct both distance
               Conductive Keratoplasty                             months. Therefore, CK appears to be             and near vision through a series of
               Conductive Keratoplasty (CK) received               relatively ineffective for the correction       concentric circular bands, each band
               FDA approval in 2002 for the treatment              of mild to moderate hyperopia even in           alternating between distance and near
               of mild spherical hyperopia between                 the medium term. Recently, three-year           vision correction.
               +0.75 D and +3.00 D with astigmatism                post-operative results of CK performed            A typical refractive multifocal IOL
               of -0.75 D or less, and in 2004 for the             in only one eye (the non-dominant eye)          comprises of concentric optical zones
               treatment of presbyopic mild hyperopes              of 10 plano presbyopic patients for near        of varying diameters. For example, the
               and emmetropes. CK is a non-laser                   vision improvement have shown that              ReZoom (Advanced Medical Optics) is
               radio      frequency-based     thermal              the procedure was safe as no eye lost           a zonal progressive IOL that
               keratoplasty procedure that shrinks                 lines of BSCVA. However, at three-years         incorporates a continuous range of
               small amounts of corneal collagen to                post-op, only 44% of eyes were within ±         foci. The multifocal area is contained
               bend and increase the refractive power              0.50 D of the intended refraction and           within the full 6.00mm optical zone
               of the cornea. Initial attempts with                the mean spherical equivalent changed           and consists of five concentric zones:
               this    technique    required    initial            from -1.31 D at the one-year post-              1, 3 and 5 are distance dominant while
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       2 and 4 are near dominant. There is           visual acuity was N5 or better in 44%                 where the IOL is misaligned or tilted.
       an aspherical transition between              of patients, binocular uncorrected                    In addition, these methods ignore the
       zones to provide a smooth change in           intermediate visual acuity was N5                     fact that presbyopes under 65 years in
       the zonal power of the lens and also          or better in 50% of patients and                      age may have some remaining
       provide intermediate vision. The              binocular uncorrected distance visual                 accommodation which is sacrificed
       addition power is equivalent to 2.60          acuity was 6/6 or better in 60%                       when the crystalline lens is replaced
       D at the spectacle plane. Due to the          of patients.                                          by an artificial implant.
       annular zones of various refractive             Multi-focal         lenses       have
       powers, the performance of refractive         discontinuous optics and create more                  Accommodative Intra-
       multifocal IOLs depends on pupil              than one image to enable both distance                Ocular Lenses                                   33
       size; the pupil size will affect image        vision and near vision correction. This               Rather than using multifocal IOLs,
       quality at both distance and near.            has been shown to reduce contrast                     another possibility might be to use a




                                                                                                                                                           3/10/08 CET
          Diffractive multifocal IOLs in             sensitivity 20 and increase night vision              monofocal IOL mechanism which can
       which distance and near corrections           disturbances. The first multifocal IOLs               vault forward and backwards on it’s
       are simultaneously present across the         were discontinued because of halo and                 haptics in order to provide the patient
       full area of the pupil are rarely used.       glare disability, refractive instability,             with accommodative ability and
       Most so-called diffractive IOLs are a         decreased contrast sensitivity and                    therefore better image quality at both
       combination of refractive and                 decreased quality of vision.18 Whilst                 distance and near. Current evidence
       diffractive lenses, including a central       there has been some improvement,                      suggests that significant ciliary body
       diffractive optical regi--on in which         current lenses have not overcome                      function remains throughout ageing. If
       concentric diffractive zones divide           many of these drawbacks. For example,                 so, replacement of the crystalline lens
       light into two diffractive orders. For        Chiam reported moderate glare in 20%                  with an intraocular lens that responds
       example, the ReSTOR (Alcon                    of ReSTOR patients and 30% of                         to ciliary body contraction should
       Laboratories) has a central 3.6mm             ReZoom patients.19 Moderate halos                     restore     some       accommodative
       diffractive optic region in which             were reported by 14% of ReSTOR                        function.
       twelve concentric diffractive zones           patients and 28% of ReZoom patients.                    Ideally, one option would be to
       on the anterior surface of the lens           Other studies have shown that                         preserve the lens capsule and fill it
       divide the light into two diffractive         approximately 4-8% of patients                        with an elastic polymer that matches
       orders. The addition power is                 experienced severe night vision                       the behaviour of a young crystalline
       equivalent to 3.20 D at the spectacle         disturbances.21,22 This is particularly               lens. However, until now, the
       plane.                                        evident in patients with large pupils or              intraocular lens optics were not
          Clinically, although multi-focal
       lenses do appear to increase the range
       of vision from distance to near, and                                                     ¤ Dominant eye:
       spectacle independence is often more                                                     Focused for distance, slightly blurred at near
       likely with use of these IOLs than
       with the standard practice of
       monocular IOLs implantation, there                                                                  ~98%
       are a few shortcomings, including a                                                                 Patients Tolerate
       limited depth of field, reduced
       contrast sensitivity and an increase in
       night vision disturbances.
          As a result of the limited depth of
       field inherent to the type of lens used,
       the patient may experience poor
       vision at certain distances. For
       example, in a study comparing
       functional vision with the ReSTOR
       and the ReZoom IOLs19 six months
       after surgery, the following results
                                                                                                           2 Brain merges two images to see near and far
       were found. With ReSTOR, binocular                                                                  without spectacles
       uncorrected near visual acuity was
       N5 or better in 88% of patients,
                                                     2 Non-dominant eye: Focused for near,
       binocular uncorrected intermediate
                                                     blurred at distance
       visual acuity was N5 or better in 24%
       of patients and binocular uncorrected
       distance visual acuity was 6/6 or             < Figure 3
       better in 46% of patients. With                 Blended Vision: Integration. Blended vision correction allows for a natural continuous focus from
       ReZoom, binocular uncorrected near              distance to near with an overlap in intermediate focus.
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                                                                                                 Accuracy         Binocular Efficacy                        Safety


                                      Extra or Astigmatism Range treated          Range           ±0.50D          6/6           N5          Contrast       Loss of    Night Vision
                Procedure           Intra ocular Correction  in study           treatable                                                  Sensitivity     ≥2 lines   Disturbances

                                       Extra           Yes         Myopes        Same as           No data        76%           95%          No data       No data       No data
                PRK Monovision12                                                PRK/LASIK

 34                                                                                                                                                        20% Dist
                PresbyLASIK13          Extra         No data       No data        No data           64%           48%           82%         Decrease       50% Near    Night halos
 3/10/08 CET




                Conductive                                           Plano         Plano
                Keratoplasty16         Extra           No         presbyopes    presbyopes          44%          100%         78% N6         No data         0%          No data


                ReSTOR IOL19           Intra        No (<1D)
                                                                   Mean SE      ~ -10.00 to                                                                               Glare
                                                                  -1.0±0.57      +8.00 D*                         46%           88%          No data       No data        Halos
                                                                                                NA (px outside
                                                                                                ±0.75D were
                                                                   Mean SE      ~ -14.00 to       excluded)                                                               Glare
                ReZoom IOL19           Intra        No (<1D)      -0.50±0.74    +8.00 DΔ                          60%           44%          No data       No data        Halos

                Tetraflex
                Accommodative          Intra           No                       ~ -15.00 to                       96%
                                                                   Not given    +14.00 D•           73%          (6/7.5)        63%          No data       No data       No data
                IOL28

                                                                   0.0 D to    Up to                                                       Increase at 6
                                       Extra       Up to -3.00D    -9.00 D     -13.0 D 0 to         91%           98%           96%         and 12 cpd       0%           None
                Laser Blended                                                           -6.00
                Vision32                                                                D cyl
                                                                   0.0 D to    Up to                                                       Increase at 3
                                       Extra       Up to -3.25D                +6.0 D
                                                                                                    79%           95%           81%                          0%           None
                                                                   +5.75 D                                                                   and 6 cpd


               * IOL power range +10.00D to +30.00 D in 0.50 D increments. Treatable range will vary depending on axial length and keratometry.
               Δ IOL power range +6.00 D to +30.00 D in 0.50 D increments. Treatable range will vary depending on axial length and keratometry.
               • IOL power range +5.00 D to +36.00 D; +5.0 to +18.0 D and +25.0 to + 36.0 D in 0.50 D increments, +18.0 to +25.0 D in 0.25 D increments and
               +31.0 D to +36.0 D in 1.0 D increments. Treatable range will vary depending on axial length and keratometry.

               < Table 1
                 Summary of available presbyopic treatments


               sufficiently elastic to change their form               increase in effective lens power of 0.80                 Recent clinical results with the
               in conjunction with the contraction of                  to 2.30 diopters (D), depending on                       Tetraflex accommodative IOL have
               the ciliary muscle.23                                   axial length and IOL power.25 However,                   shown that only 50.6% of eyes
                 One currently available option is to                  a number of investigations have shown                    achieved 6/6 or better uncorrected
               use specific intraocular lenses in which                that objective measurements are                          distance visual acuity and 48.1% of
               the haptic design is such that it is able               unable to demonstrate any significant                    eyes achieved N8 or better uncorrected
               to move the optic forward along the                     forward movement of the IOL.26 The                       near      visual     acuity.28 Finally,
               optical axis of the eye, thereby                        average forward movement produced                        accommodative IOLs have not yet
               increasing the effective power of the eye               by an accommodative stimulus was                         incorporated design features that are
               and aiming to provide the patient with                  0.010mm, and the maximum forward                         now available in monofocal lenses to
               pseudophakic accommodation. These                       movement using pilocarpine was                           prevent      posterior    sub-capsular
               IOLs have hinged optics designed to                     0.455mm.27 Therefore, in patients                        opacification (PCO), and subsequently
               allow the IOL to move forward as a                      showing good near vision with                            have shown very high rates.29
               result of increased vitreous pressure                   accommodative IOLs, it is unlikely                         Although accommodative IOLs
               and/or ciliary body contraction in                      that this was due to forward movement                    appear to reduce the incidence of night
               keeping with the Coleman hydraulic                      of the lens; these patients might be                     vision problems such as halos and glare
               catenary     suspension      theory     of              using other pseudoaccommodative                          compared to multifocal IOLs, while
               accommodation.24             Theoretical                factors such as myopic astigmatism,                      performing better than monofocal IOLs,
               calculations     suggest    a    forward                pupillary miosis, or the results might                   the accommodative ability they
               movement of 1.00mm equates to an                        be influenced by test conditions.                        provide can be limited.27
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       New approaches                                where the brain can merge the images           6/6 at distance and 95% could read N5
       New developments suggest the                  of the two eyes. Therefore, much less          at near.
       possibility of a laser surgical technique     suppression is required and there is no          Laser Blended Vision can be applied
       with significantly less disadvantages         dissociation between the eyes. This has        to patients with spherical refraction
       than both intra-ocular implants and           been evidenced by measuring a                  between -13.00 D and +6.00 D, and
       existing laser refractive presbyLASIK         statistically significant improvement in       with cylindrical refraction up to -6.00
       procedures. Recent laser refractive           the distance UCVA binocularly when             D. Further, Laser Blended Vision can
       surgery       approaches      focus    on     compared to that of the distance eyes          be applied to patients who have
       modifying the asphericity of the              monocularly, which demonstrates the            already had cataract surgery and are
       cornea30 which has the advantage of           presence       of    neural     binocular      implanted with monofocal IOL lenses.            35
       maintaining more natural continuous           summation of images from each eye.33
       optics. The primary objective in the          Further, due to the increased depth of         Conclusion and




                                                                                                                                                    3/10/08 CET
       aspheric correction of presbyopia is to       field in both eyes, it was reported that       future developments
       create an optical surface that can            the distance vision of the near eyes and       Advances in the treatment of
       modify the optical properties of the          the near vision of the distance eyes           presbyopia have brought a multitude of
       entire eye to improve the depth of            were better than might be expected.33          refractive corrective options to the
       field.31, 32                                  At distance, for a typical eye, 0.25 D of      patient (table 1), and techniques are
          Research in this area was adopted by       myopic defocus results in the loss of          constantly improving. While most
       Reinstein et al in 2003 in collaboration      one logMAR line of UCVA.34 Hence, an           procedures are efficient in enhancing
       with Carl Zeiss Meditec (Jena,                untreated eye with myopia of -1.50 D           the ability of achieving distance and
       Germany), with the aim of improving           would be expected to achieve distance          near correction, many also come with
       on the concept of simple asphericity or       UCVA of 6/24. The near eyes in this            significant side effects and drawbacks.
       prolaticity      to     develop      more     study had a mean refraction of -1.32 ±           Currently, it seems that the best
       sophisticated non-linear aspheric             0.61 D, but the mean distance UCVA             outcomes, lowest complications rates
       ablation profiles. This approach              was 6/13 (17.7% achieved a distance            and least side effects are afforded by
       enables a less extreme method of              UCVA of 6/6 or better, 46.9% achieved          non-linear aspheric refractive corneal
       monovision which also allows the              6/12 or better and 80.5% achieved 6/19         surgery by Laser Blended Vision. This
       combined correction of presbyopia             or better). At near, a 55-year-old would       technique offers better refractive
       and any existing refractive error to be       be expected to need a near addition in         accuracy, minimal night vision
       more effective.                               the range of +1.50 to +2.25 D.35 The           disturbances, better control of optical
          The non-linear aspheric profile            mean patient age in this study was 56          centration, no reduction and possibly
       treatment is designed to increase the         years and the mean achieved spherical          an increase in contrast sensitivity, and
       prolate shape of the cornea, but unlike       equivalent in the non-dominant eye             lower surgical risks than intraocular
       simple (linear) aspheric profiles, the        was only -1.32 ± 0.61 D, while still           surgery. In my opinion, Laser Blended
       ablation depth required is much lower.        enabling 100% of patients to read              Vision represents the best modality to
       Increasing       the     prolaticity   or     newsprint (N8) and 80.7% to read N5.           help restore the youthful functionality
       asphericity of the cornea increases the          Termed ‘Laser Blended Vision’ rather        which presbyopia compromises.
       amount        of   negative     spherical     than monovision (because there is
       aberration (OSA notation) and hence           fusion between the two eyes at mid-            About the author
       increases depth of field. The increased       distances) this mode of correction has         Professor Dan Reinstein has published
       depth of field in each eye means that         shown a 98% tolerance rate on                  extensively in the field of refractive
       good binocular near and distance              preoperative screening. The technique          surgery. In 2002, he established the
       vision can be achieved with a lower           not only facilitates the tolerance of this     London Vision Clinic, where he
       degree       of   anisometropia      than     mode of correction, it also maintains or       continues as medical director. Professor
       traditional monovision. This results in       improves contrast sensitivity and              Reinstein has developed advanced
       one eye being clearly focused for             prevents night vision disturbances             excimer      applications      including
       distance vision, but with reduced blur        from being induced.                            biomechanically based ablation profiles
       at near, and the other eye being clearly         In addition, when distance and near         using non-linear aspherics for treating
       focused for near vision, but with             vision were measured post-operatively          very high myopia with very low
       reduced blur at distance. Unlike the          no eye lost two lines of BSCVA in a            induction of aberrations, and very low
       traditional monovision approach, the          study including 343 patients.36 In             tissue consumption, and has further
       increase in depth of field is such that       myopes, 98% of patients without                developed these to enable presbyopic
       the range of clear vision achieved by         correction could read 6/6 at distance          LASIK based on increasing the depth of
       the distance eye and the near eye             and 96% could read N5 at near. In              field of the cornea. Both these
       overlap at intermediate distances (see        hyperopes, 95% of patients without             applications have been adopted by Carl
       Figure 3).                                    correction could read 6/6 at distance          Zeiss Meditec for future product releases.
          The major advantage of this method         and      81%       could      read     N5
       is in creating an intermediate and far-       at near. 37 In plano patients, 96% of          References
       intermediate distance zone of fusion,         patients without correction could read         See www.optometry.co.uk/references
CETBLUE OCTOBER 5.qxd:CET                    1/10/08         11:36      Page 36




                                    CONTINUING

               CET                  EDUCATION &
                                    TRAINING                                                                                               Sponsored by:


               This issue CET: Free ✔ Worth 2 standard CET points
                                                To gain more standard CET points for this year’s PAYL series, enter online at: www.otcet.co.uk or ¥ 0207 878 2412




                 Module questions                                                                                                                     Course code: c-8162
                 Please note, there is only one correct answer. Enter online or by form provided
                 An answer return form is included in this issue. It should be completed and returned to CET initiatives (c-8162)
                 OT, Ten Alps plc, 9 Savoy Street, London WC2E 7HR by October 29 2008.
                1.   What is the average amplitude of accommodation of a 60-year-old subject?             7. Which presbyopic treatment has been reported to give the worst outcomes
                a.   between 2.00 D and 2.90 D                                                               in terms of safety (loss of 2 lines or more of BSCVA)?
                b.   between 0.00D and 2.00 D                                                             a. PresbyLASIK
                c.   between 2.00 D and 5.00 D                                                            b. Conductive Keratoplasty
                d.   between 3.00 D and 3.90 D                                                            c. Multifocal IOLs
 36                                                                                                       d. Laser Blended Vision
                2. What percentage of patients can tolerate monovision contact lenses
 3/10/08 CET




                   correction?                                                                            8. Which one of the following treatment(s) have not been reported to cause
                a. 60%                                                                                       significant night vision disturbances?
                b. 80%                                                                                    a. Diffractive IOLs
                c. 90%                                                                                    b. Refractive IOLs
                d. 98%                                                                                    c. Laser Blended Vision
                                                                                                          d. PresbyLASIK
                3. Conductive Keratoplasty has been shown to be effective for the permanent
                   treatment of:                                                                          9. Which one of the following is correct regarding Accommodative IOLs?
                a. Astigmatism                                                                            a. Accommodative IOLs are able to move forward along the optical axis
                b. Spherical hyperopia                                                                       of the eye
                c. Myopia                                                                                 b. Accommodative IOLs are able to move upwards
                d. None of the above                                                                      c. Accommodative IOLs are able to move downwards
                                                                                                          d. Ciliary body function is obselete by the age of 40 years
                4. How do Laser Blended Vision procedure and Multifocal presbyLASIK
                   procedure differ?                                                                      10.   Which one of the following is incorrect regarding Laser Blended Vision?
                a. Multifocal presbyLASIK is a corneal refractive surgery technique that                  a.    it creates an aspheric corneal surface
                   creates discontinuous optics and more than one focal plane                             b.    it increases the depth of field of both the distance eye and the near eye
                b. Laser Blended Vision is a corneal refractive surgery technique that creates            c.    it creates a zone of fusion between the two eyes
                   discontinuous optics and more than one focal plane                                     d.    it can only be used in myopes
                c. Multifocal presbyLASIK is independent of pupil size
                d. Laser Blended Vision is a corneal refractive surgery technique that                    11. What percentage of patients can tolerate Laser Blended Vision based on
                   decreases depth of field                                                                   pre-operative screening?
                                                                                                          a. 60%
                5. What presbyopic treatments are currently available that can also correct               b. 70%
                   significant astigmatism?                                                               c. 80%
                a. Conductive keratoplasty                                                                d. 98%
                b. Laser Blended Vision
                c. Accommodative IOLs                                                                     12. In Laser Blended Vision, increased depth of field is achieved by:
                d. None of the above                                                                      a. correcting the central part of the treatment zone on the cornea for near
                                                                                                              vision, and the peripheral part of the treatment zone on the cornea for
                6. Which presbyopic treatment is the most capable of giving the best refractive               distance vision
                   control of sphere and cylinder (accuracy of spherical equivalent within 0.50           b. correcting all of the eye's higher order aberrations
                   D of the intended)?                                                                    c. modifying the asphericity of the cornea
                a. PresbyLASIK                                                                            d. increasing the size of the ablation zone
                b. Conductive Keratoplasty
                c. Multifocal IOLs
                d. Laser Blended Vision



                 Please complete on-line by midnight on October 29 2008 - You will be unable to submit exams after this date – answers to the module will be published in our October 31 issue
CETBLUE OCTOBER 5.qxd:CET   1/10/08    11:36    Page 37




                                                                                                    CONTINUING

       Sponsored by:                                                              CET               EDUCATION &
                                                                                                    TRAINING

                                                                                  This issue CET: Free ✔ CET points
                                                                                                         Worth 2 standard

                             To gain more standard CET points for this year’s PAYL series, enter online at: www.otcet.co.uk or ¥ 0207 878 2412




                                                                                                                                                 37




                                                                                                                                                 5/09/08 CET

				
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