Pauline Kang

Peripheral Refraction in Myopic Children Wearing Orthokeratology and Gas-permeable Lenses

Purpose. To investigate changes in peripheral refraction after orthokeratology (OK) and rigid gas-permeable (GP) lens wear in progressing myopic children and to compare these peripheral defocus changes with reported changes in adults wearing OK. Methods. Sixteen myopic children subjects were fitted with an OK lens in one eye for overnight wear and a GP lens in the other eye for daily wear. Central and peripheral refraction were measured at baseline and then after 3 mo of lens wear. Results. At baseline, myopic children showed relative peripheral hyperopia compared with central refraction at and beyond 20° in the temporal visual field (VF) and 30° in the nasal VF. Three months of OK lens wear produced hyperopic shifts in refraction between 30° in the temporal VF and 20° in the nasal VF. Peripheral refraction was similar to center at all positions in the temporal VF while remaining significantly myopic at all locations in the nasal VF. No change in either central or peripheral refraction was found after 3 mo in the eye assigned for GP lens wear. Conclusions. OK significantly reduced myopia in the central 20° VF in myopic children, converting relative peripheral hyperopia measured at baseline to relative peripheral myopia. These changes in children are similar to changes reported in myopic adults wearing OK lenses. No change in either central or peripheral refraction was found after 3 mo of daily GP lens wear. OK lenses can be used to induce myopic defocus in the periphery in myopic children and may thus provide a potential mechanism for myopia control.

Myopia control during orthokeratology lens wear in children using a novel study design.

PURPOSE To investigate the effect of overnight orthokeratology (OK) contact lens wear on axial length growth in East Asian children with progressive myopia. DESIGN A prospective, randomized, contralateral-eye crossover study conducted over a 1-year period. PARTICIPANTS We enrolled 26 myopic children (age range, 10.8-17.0 years) of East Asian ethnicity. METHODS Subjects were fitted with overnight OK in 1 eye, chosen at random, and conventional rigid gas-permeable (GP) lenses for daytime wear in the contralateral eye. Lenses were worn for 6 months. After a 2-week recovery period without lens wear, lens-eye combinations were reversed and lens wear was continued for a further 6 months, followed by another 2-week recovery period without lens wear. Axial eye length was monitored at baseline and every 3 months using an IOLMaster biometer. Corneal topography (Medmont E300) and objective refraction (Shin-Nippon NVision-K 5001 autorefractor) were also measured to confirm that OK lens wear was efficacious in correcting myopia. MAIN OUTCOME MEASUREMENTS Axial length elongation and myopia progression with OK were compared with conventional daytime rigid contact lens wear. RESULTS After 6 months of lens wear, axial length had increased by 0.04±0.06 mm (mean±standard deviation) in the GP eye (P=0.011) but showed no change (-0.02±0.05 mm) in the OK eye (P=0.888). During the second 6-month phase of lens wear, in the OK eye there was no change from baseline in axial length at 12 months (-0.04±0.08 mm; P=0.218). However, in the GP eye, the 12-month increase in axial length was significant (0.09±0.09 mm; P<0.001). The GP lens-wearing eye showed progressive axial length growth throughout the study. CONCLUSIONS These results provide evidence that, at least in the initial months of lens wear, overnight OK inhibits axial eye growth and myopia progression compared with conventional GP lenses. Apparent shortening of axial length early in OK lens wear may reflect the contribution of OK-induced central corneal thinning, combined with choroidal thickening or recovery due to a reduction or neutralization of the myopiogenic stimulus to eye growth in these myopic children.

Peripheral Refraction in Different Ethnicities

PURPOSE Peripheral refraction is commonly used to infer retinal shape. Because of the different prevalence of myopia in the white compared with East Asian populations, peripheral refraction along the horizontal meridian was compared in white and East Asian young adults with emmetropic, low myopic, and moderately myopic refractive errors. METHODS Thirty-five white and 37 East Asian subjects were recruited with central refraction between +1.00 DS and -5.50 DS and ≤ -1.50 DC. Central and peripheral noncycloplegic autorefraction was measured along the horizontal meridian at 5° intervals up to ± 35°, and corneal topography maps were also quantified. RESULTS There were no significant differences between whites and East Asians in peripheral refraction profiles in the emmetrope and low myope groups, which had peripheral myopic and emmetropic refraction, respectively. However, in the moderate myope group, there was a statistically significant difference between whites and East Asians in peripheral refraction, which was generally hyperopic. East Asian moderate myopes had more relative peripheral hyperopia than did whites of similar central refractive error. Corneal shape and power were comparable between white and East Asian subjects in the three refractive groups. CONCLUSIONS East Asian moderate myopes have a greater degree of relative peripheral hyperopia and hence a more prolate ocular shape than do white subjects of similar central refractive error. Differences in ocular shape may play a role in the greater propensity for East Asians to develop and progress in myopia compared with whites.

Effect of single vision soft contact lenses on peripheral refraction.

Purpose. To investigate changes in peripheral refraction with under-, full, and over-correction of central refraction with commercially available single vision soft contact lenses (SCLs) in young myopic adults. Methods. Thirty-four myopic adult subjects were fitted with Proclear Sphere SCLs to under-correct (+0.75 DS), fully correct, and over-correct (−0.75 DS) their manifest central refractive error. Central and peripheral refraction were measured with no lens wear and subsequently with different levels of SCL central refractive error correction. Results. The uncorrected refractive error was myopic at all locations along the horizontal meridian. Peripheral refraction was relatively hyperopic compared to center at 30 and 35° in the temporal visual field (VF) in low myopes and at 30 and 35° in the temporal VF and 10, 30, and 35° in the nasal VF in moderate myopes. All levels of SCL correction caused a hyperopic shift in refraction at all locations in the horizontal VF. The smallest hyperopic shift was demonstrated with under-correction followed by full correction and then by over-correction of central refractive error. An increase in relative peripheral hyperopia was measured with full correction SCLs compared with no correction in both low and moderate myopes. However, no difference in relative peripheral refraction profiles were found between under-, full, and over-correction. Conclusions. Under-, full, and over-correction of central refractive error with single vision SCLs caused a hyperopic shift in both central and peripheral refraction at all positions in the horizontal meridian. All levels of SCL correction caused the peripheral retina, which initially experienced absolute myopic defocus at baseline with no correction, to experience absolute hyperopic defocus. This peripheral hyperopia may be a possible cause of myopia progression reported with different types and levels of myopia correction.

Time course of the effects of orthokeratology on peripheral refraction and corneal topography

To describe the time course of changes in both peripheral refraction and corneal topography in myopic adults wearing myopic orthokeratology (OK) lenses.

Can manipulation of orthokeratology lens parameters modify peripheral refraction

Purpose To investigate changes in peripheral refraction, corneal topography, and aberrations induced by changes in orthokeratology (OK) lens parameters in myopes. Methods Subjects were fitted with standard OK lenses that were worn overnight for 2 weeks. Peripheral refraction, corneal topography, and corneal surface aberrations were measured at baseline and after 14 nights of OK lens wear. Subsequent to a 2-week washout period, subjects were refitted with another set of lenses where one eye was randomly assigned to wear an OK lens with a smaller optic zone diameter (OZD) and the other eye with a steeper peripheral tangent. Measurements were taken again at a second baseline and after 14 days of overnight wear of the second OK lens set. Results Standard OK lenses with a 6-mm OZD and 1/4 peripheral tangent caused significant changes in both peripheral refraction and corneal topography. Significant hyperopic shift occurred in the central visual field (VF) while a myopic shift was found at 35 degrees in the nasal VF. OK induced significant reductions in corneal power at all positions along the horizontal corneal chord except at 2.4 mm nasal where there was no significant change and at 2.8 mm nasal where there was an increase in corneal refractive power. A positive shift in spherical aberration was induced for all investigated lens designs except for the 1/2 tangent design when calculated over a 4-mm pupil. Reducing OZD and steepening the peripheral tangent did not cause significant changes in peripheral refraction or corneal topography profiles across the horizontal meridian. Conclusions OK lenses caused significant changes in peripheral refraction, corneal topography, and corneal surface aberrations. Modifying OZD and peripheral tangent made no significant difference to the peripheral refraction or corneal topography profile. Attempting to customize refraction and topography changes through manipulation of OK lens parameters appears to be a difficult task.

The effect of multifocal soft contact lenses on peripheral refraction.

Purpose To compare changes in peripheral refraction with single-vision (SV) and multifocal (MF) correction of distance central refraction with commercially available SV and MF soft contact lenses (SCLs) in young myopic adults. Methods Thirty-four myopic adult subjects were fitted with Proclear Sphere and Proclear Multifocal SCLs to correct their manifest central refractive error. Central and peripheral refraction were measured with no lens wear and subsequently with the two different types of SCL correction. Results At baseline, refraction was myopic at all locations along the horizontal meridian. Peripheral refraction was relatively hyperopic compared with center at 30 and 35 degrees in the temporal visual field (VF) in low myopes, and at 30 and 35 degrees in the temporal VF, and 10, 30, and 35 degrees in the nasal VF in moderate myopes. Single-vision and MF distance correction with Proclear Sphere and Proclear Multifocal SCLs, respectively, caused a hyperopic shift in refraction at all locations in the horizontal VF. Compared with SV correction, MF SCL correction caused a significant relative myopic shift at all locations in the nasal VF in both low and moderate myopes and also at 35 degrees in the temporal VF in moderate myopes. Conclusions Correction of central refractive error with SV and MF SCLs caused a hyperopic shift in both central and peripheral refraction at all positions in the horizontal meridian. Single-vision SCL correction caused the peripheral retina, which initially experienced absolute myopic defocus at baseline with no correction to experience an absolute hyperopic defocus. Multifocal SCL correction resulted in a relative myopic shift in peripheral refraction compared with SV SCL correction. This myopic shift may explain recent reports of reduced myopia progression rates with MF SCL correction.

New Perspective on Myopia Control with Orthokeratology.

Purpose To compare peripheral refraction along both the horizontal and vertical retinal meridians before and after orthokeratology (OK) lens wear. Methods Nineteen young adult myopic subjects (mean age, 28 ± 7 years) were fitted with OK lenses in both eyes. Central and peripheral refraction and corneal topography measurements were taken before and after 14 nights of OK. All measurements were taken with no correction or OK lens in place. Results At baseline before OK, peripheral spherical equivalent refraction (M) across the horizontal meridian did not vary significantly from center. M across the vertical meridian was more myopic than the center (p < 0.05). After OK, there was a significant hyperopic shift in M (p < 0.001); both meridians now experienced myopic peripheral refraction. At baseline, J180 across the horizontal meridian was more negative than the center, and along the vertical meridian, it was more positive than the center (all p < 0.05). At baseline, J45 was more positive than center with increased eccentricity in the temporal and inferior retina and more negative than center with increased eccentricity in the nasal and superior retina. Orthokeratology caused greater rate of change of peripheral J180 across both retinal meridians (p < 0.001). Furthermore, compared with baseline, J45 became more positive in the nasal and superior retina and more negative in the temporal and inferior retina (all p < 0.05). Conclusions Orthokeratology lenses induced significant changes in peripheral refraction along the horizontal and vertical meridians. As peripheral myopia was measured at baseline along the vertical meridian, the results of our study suggest that inducing greater degrees of myopic defocus on to the peripheral retina, more than habitually experienced, may be required for effective myopia control. Further investigation into the critical threshold of retinal area receiving myopic defocus and the impact of duration of exposure is necessary to improve the efficacy of current myopia control treatments.

Acute and short-term changes in visual function with multifocal soft contact lens wear in young adults

PURPOSE To characterise the effects on accommodation and binocular vision in young adults of 2 distance centre multifocal soft contact lenses (MFSCLs), differing in add power. METHODS Twenty-four young adult myopes (18-28 years; 20 females, 4 males) had baseline visual acuity, accommodation, near phoria, fixation disparity and stereopsis data collected with single vision (SV) SCLs. The same set of measurements was repeated immediately after subjects were fitted with each of two MFSCLs (with either +1.50 or +3.00 D add), and after 2 weeks of daily wear in each case. The order of testing was randomised and a one-week washout period was allowed between the first and second MFSCL trials. RESULTS Differences in distance and near acuities with MFSCLs compared to SVSCLs were small and clinically insignificant. Compared to responses with SVSCLs, MFSCLs increased accommodative lags with this change reaching statistical significance for the +1.50 D add lens. Furthermore, both MFSCLs induced significant shifts in near phorias in the exo direction. Finally, there were no significant differences in stereopsis and fixation disparity with MFSCLs compared to SVSCLs. CONCLUSION Differences in acuities, accommodation accuracy and binocular posture with MFSCLs compared to SVSCLs were clinically small and mostly not significant. These results predict good tolerance of MFSCLs in young patients fitted with them for myopia control.

Changes to corneal aberrations and vision after Presbylasik refractive surgery using the MEL 80 platform.

PURPOSE To investigate changes to corneal surface aberrations and vision between PresbyLASIK and LASIK for correction of presbyopia using the MEL 80 platform (Carl Zeiss Meditec, Jena, Germany). METHODS The retrospective data of 31 patients who underwent PresbyLASIK (the PresbyLASIK group) between January 2009 and November 2011 and 20 matched patients who underwent LASIK (the LASIK group) were analyzed for changes to refraction, corrected distance visual acuity, and corneal surface wavefront aberrations calculated over 4- and 6-mm pupils. Outcomes at the 3-month follow-up visit were compared to data collected immediately prior to surgery and between PresbyLASIK and LASIK correction. Associations between induced corneal aberrations and best spherical equivalent refraction were explored. RESULTS PresbyLASIK and LASIK significantly reduced refractive error in both myopes and hyperopes. Residual refractive error was not significantly different between treatment groups, except for spherical equivalent refraction, which was significantly more myopic following LASIK treatment compared to PresbyLASIK in myopes. There was no significant difference in postoperative corrected distance visual acuity between groups. LASIK and PresbyLASIK induced positive spherical aberration in myopes and negative spherical aberration in hyperopes, with significant differences between treatments only apparent in myopes when analyzed over a 4-mm pupil (PresbyLASIK group: 0.07 ± 0.06 µm; LASIK group: 0.03 ± 0.04 µm, P < .05). In hyperopes, induced spherical aberration was more highly associated with refractive change after LASIK (r = 0.82, P < .05) than PresbyLASIK (r = 0.64, P < .001); instead PresbyLASIK led to a more consistent shift of approximately 0.3 µm independent of induced change to refraction. CONCLUSIONS PresbyLASIK using the MEL 80 platform induced significant changes in spherical aberration in myopes and hyperopes. PresbyLASIK appears to offer an improved response over LASIK when correcting myopes due to an apparent increase in depth of focus resulting from changes in spherical aberration. For hyperopes, PresbyLASIK provides a more consistent spherical aberration effect independent of refractive change.