Ultraviolet radiation transmission of soft disposable contact lenses and ISO 18369: claims and compliance.

CLINICAL RELEVANCE: This study was carried out to provide advice to eye care practitioners on those soft disposable contact lenses that comply with the Class 1 or Class 2 requirements of the international standard ISO 18369 for ultraviolet radiation protection. BACKGROUND: This study was carried out to provide advice to eye care practitioners on those soft disposable contact lenses that comply with the Class 1 or Class 2 requirements of the international standard ISO 18369 for ultraviolet radiation (UVR) protection and to validate any claims made. It is intended to be used when a patient needs or requests UVR protection. A revised ISO 18369-3 was published in 2017. There is no Australian adoption nor equivalent. METHODS: The direct spectral transmittance of three specimens of each of the twenty soft disposable contact lens types available in Australia in 2018 was measured in saline in a quartz cuvette with a dual beam spectrophotometer from 200-780 nm. Transmittance values for each material were averaged and scaled according to a single measurement of its transmittance in the visible spectrum (380-780 nm). Based on the ISO 18369-3:2017 criteria, lens materials were denoted as Class 1, Class 2 or non-UVR protectors. This classification was compared with any claim made by the manufacturer. RESULTS: All claims of the manufacturers for Class 1 or Class 2 were valid. There were no examples of any missed opportunity to make a claim. Some claims were so general as to be untestable. Some numerical claims appeared to hide that only a Class 2 claim could be made. CONCLUSIONS: Claims of Class 1 or Class 2 were found to be appropriate. There were no missed opportunities to claim. UV protection claims that were not in the ISO 18369-3 format may be taken as Class 2 compliance but not Class 1 compliance. A two-class system of UV protectors and non-UV protectors may serve practitioners and their patients better.

Manipulation of Front-Surface Profile of Scleral Contact Lenses to Alter Peripheral Refraction.

SIGNIFICANCE: The front optic zone diameter of scleral contact lenses was manipulated to mimic the central treatment zone induced by orthokeratology contact lens wear, to explore potential effects on the peripheral refraction profile. PURPOSE: The purpose of this study was to investigate effects on the peripheral refraction profile of changing front optic zone diameters of scleral contact lenses. METHODS: Twelve young adults were fitted with scleral contact lenses (diameter, 16.5 mm) with two front optic zone diameters (6 and 4 mm) on one eye only on 2 separate days. Both lenses were fabricated with front optic zone power of -3.00 D and plano power outside the optic zone to mimic the orthokeratology treatment effect. All lenses had the same spherical back-surface design with a toric lens periphery. Peripheral refraction was measured at 10° increments along horizontal (±35°) and vertical (±30°) meridians before lens insertion and after 10 minutes of lens wear. Mixed-model analysis and post hoc t tests with Bonferroni correction were performed. RESULTS: Compared with baseline, no significant change in relative spherical equivalent refraction M was observed with 6-mm optic zone lenses along the horizontal meridian. However, a significant difference in relative M profile was found with 4-mm optic zone lenses (P = .009). M became myopic at all locations in the nasal visual field (P < .05) except at 35°. In contrast, compared with baseline, no significant changes in relative M were found with either 6- or 4-mm optic zone lenses along the vertical meridian. CONCLUSIONS: The greater myopic shift in relative peripheral refraction with 4-mm compared with 6-mm front optic zone lenses suggests that a reduced treatment zone diameter in orthokeratology may induce more myopic peripheral refraction changes. This may guide us toward novel orthokeratology lens designs for more effective myopia control.

Corneal Total and Epithelial Thickness Measured by Sonogage Ultrasound Pachometry and High-resolution Optical Coherence Tomography.

SIGNIFICANCE: This research questions the validity of using the Sonogage ultrasound (US) pachometer to measure corneal epithelial thickness and coincidentally provides confirmation for the conventional view of the mechanism of orthokeratology (OK) based on central epithelial thinning. PURPOSE: The Sonogage (Corneo-Gage Plus 1) pachometer uses A-scan US to measure total corneal thickness. It is claimed that this instrument can also measure corneal epithelial thickness. We sought to validate this claim by comparing total and epithelial thickness measurements with the Sonogage with those obtained with high-resolution optical coherence tomography (OCT). METHODS: Fourteen non-contact lens wearers and 14 subjects who had worn Paragon CRT OK lenses overnight for greater than 1 month were recruited. Three OCT and five US measurements were taken in one eye of each subject. Depending on normality of data, paired t tests or Wilcoxon tests were used to compare total and epithelial thicknesses measured with the Sonogage pachometer and the Tomey Casia OCT. Pearson or Spearman correlation analyses were used to examine relationships between measurements obtained with the two instruments. RESULTS: There was a significant difference in total corneal thickness measurements between the two instruments. Although a significant correlation was found (r = 0.916, P < .001), the Sonogage consistently measured greater total corneal thickness than did the OCT (+19.5 ± 9.2 µm; P < .001). Epithelial thickness using the Sonogage showed little variation (range, 46.4 to 50.0 µm), whereas epithelial thickness using the OCT ranged from 30.7 to 54.7 µm. There was no significant correlation between epithelial thicknesses obtained with the two instruments (r = -0.135, P = .49). Epithelial thickness measured by OCT was significantly thinner in OK wearers (35.8 ± 2.8 µm) than in nonlens wearers (46.7 ± 4.5 µm, P < .001). CONCLUSIONS: The Sonogage is not able to measure epithelial thickness in vivo, returning essentially identical measurements over a range of epithelial thicknesses. Optical coherence tomography measurements confirm the conventional view of the mechanism of OK based on central epithelial thinning.

Changes in corneal subbasal nerve morphology and sensitivity during orthokeratology: Recovery of change.

PURPOSE: To investigate the recovery of orthokeratology (OK)-induced changes in corneal nerve morphology and sensitivity following lens wear discontinuation, over a 3-month period. METHODS: Sixteen myopic subjects who wore OK lenses during sleep for 3 months discontinued lens wear for 3 months. Corneal nerve morphology and sensitivity were assessed on the right eye only 3 h after waking at the pre-lens wear baseline and after lens wear discontinuation. Corneal nerve fiber density (NFD) and global nerve fiber orientation (GNFO) were assessed by sampling a 1 mm2 area of the subbasal nerve plexus at the corneal apex and temporal mid-periphery using in vivo confocal microscopy. Corneal sensitivity was measured using the Cochet-Bonnet aesthesiometer at similar corneal locations. RESULTS: Significant changes in corneal sensitivity, NFD, and GNFO were observed at various corneal locations during the lens wear discontinuation period. In the central cornea, NFD and corneal sensitivity increased during the 3-month non-lens wear period (p < 0.01); no significant changes in NFD or corneal sensitivity were noted in the mid-peripheral cornea. Central corneal sensitivity recovered to pre-lens wear levels after 1 month of non-lens wear. Central NFD appeared to remain slightly decreased after 3 months of non-lens wear compared to pre-lens wear levels, but this difference did not reach statistical significance (p = 0.09). GNFO did not change significantly at the central cornea during the 3-month non-lens wear period, but altered in a counter-clockwise rotational direction (reversal of OK-induced change) at the mid-peripheral cornea (p < 0.05), although it did not appear to fully recover to pre-lens wear orientation (p = 0.05). CONCLUSIONS: OK lens-induced reduction in corneal sensitivity recovers with cessation of lens wear, returning to pre-lens wear levels shortly after lens wear discontinuation. Changes to nerve morphology induced by OK lens wear, however, appear to recover more slowly towards pre-lens wear levels. This requires confirmation in a longer non-lens wear period.

Changes in Corneal Subbasal Nerve Morphology and Sensitivity During Orthokeratology: Onset of Change.

PURPOSE: To investigate changes in corneal subbasal nerve fiber density and orientation during a 3-month orthokeratology (OK) lens wear period and their relationship with concurrent changes in corneal sensitivity. METHODS: Sixteen subjects wore overnight OK lenses for 90 days and were assessed at baseline, Day 30, and Day 90. Nerve images at the corneal apex and temporal mid-periphery were captured from the right eye only using in vivo confocal microscopy and analyzed to calculate nerve fiber density (NFD) and global nerve fiber orientation (GNFO). Corneal sensitivity was measured using the Cochet-Bonnet aesthesiometer at similar corneal locations. Control groups of non-lens (NL) wearing and conventional rigid gas-permeable (GP) lens-wearing subjects were also examined. RESULTS: Significant changes in NFD, GNFO and corneal sensitivity were observed during OK lens wear over the study period. In the central cornea, both NFD and corneal sensitivity decreased by Day 30, with further reductions at Day 90. Reduced NFD was associated with reduced corneal sensitivity. In the mid-peripheral cornea only, GNFO was rotated in a clockwise direction at Day 30, with further rotation at Day 90. Corneal sensitivity reduction plateaued by Day 30. In the GP lens-wearing subjects, only corneal sensitivity decreased by Day 30 at both corneal locations. No changes were observed in the NL control subjects. CONCLUSIONS: Alterations in corneal nerve morphology occur rapidly with commencement of OK lens wear and appear to underpin functional sensitivity loss. Nerve fiber orientation can provide a useful index for changes in corneal nerve morphology.

Reduced Corneal Sensitivity and Sub-Basal Nerve Density in Long-Term Orthokeratology Lens Wear.

OBJECTIVES: To investigate changes in corneal sensitivity and nerve morphology in orthokeratology (OK) contact lens wear. METHODS: In a cross-sectional study, 54 subjects (aged 18-45 years) were grouped into three categories: nonlens (NL), soft lens (SCL), and OK lens wearers. Corneal sensitivity was measured at the corneal apex and 2.5 mm temporal to the apex using the Cochet-Bonnet aesthesiometer. Corneal nerve morphology was assessed by sampling a 1 mm area of the corneal sub-basal nerve plexus using the Heidelberg Retinal Tomograph with Rostock Corneal Module at the corneal apex and 2.5 mm temporal to the apex. Nerve fiber density (NFD) was calculated by measuring the total length of nerve fibers per square millimeter using Image-Pro Analyser. Comparisons between groups were made using mixed analysis of variance and post hoc paired t tests with Bonferroni correction or the Kruskal-Wallis test and post hoc Mann-Whitney U tests as appropriate. RESULTS: There was a significant difference in corneal sensitivity between the three groups (P=0.027). Central threshold was significantly higher in the OK than NL group (0.69±0.42 g/mm vs. 0.45±0.12 g/mm; P=0.048). Mid-peripheral threshold was not different between the three groups (P>0.05). There was a significant difference in NFD between the three groups (P<0.001). Central NFD was significantly less in the OK than NL and SCL groups (OK: 17.89±4.42 mm/mm, NL: 25.87±5.00 mm/mm; SCL: 24.52±4.93 mm/mm; P<0.001). Mid-peripheral NFD was not different between the three groups (P>0.05). CONCLUSIONS: Long-term OK lens wear is associated with a decrease in central corneal sensitivity and NFD. The mechanism underlying refractive change during OK treatment seems to impact both corneal sensitivity and nerve morphology.

Treatment Zone Decentration During Orthokeratology on Eyes with Corneal Toricity.

PURPOSE: To compare the magnitude of treatment zone decentration between eyes with minimally toric corneas (≤1.50 DC, LoTor group) and eyes with moderately toric corneas (1.50 to 3.50 DC, HiTor group) after a single overnight wear of spherical orthokeratology lenses. METHODS: In the LoTor group, 21 participants (9 M, 12 F, 20-40 years) were fitted using a conventional fitting approach based on the flat corneal meridian. In the HiTor group, 12 participants (5 M, 7 F, 19-45 years) were fitted using the conventional fitting method in one eye (HiTor group I) and the other eye was fitted with a lens with slightly deeper sagittal height (HiTor group II). In all groups, BE spherical orthokeratology trial contact lenses (Boston XO) were used and corneal topography data (Medmont E300) were obtained at baseline and after a single overnight wear. The magnitude of treatment zone decentration relative to vertex normal was determined from corneal topography refractive power difference maps. Treatment zone parameters including magnitude and direction of decentration were analyzed and related to baseline corneal parameters. RESULTS: After a single overnight wear, the mean magnitude of treatment zone decentration was 0.48 ± 0.20 mm in the LoTor group, 1.06 ± 0.57 mm in HiTor group I, and 0.95 ± 0.44 mm in HiTor group II. Treatment zone decentration in the LoTor group was significantly different from HiTor group I (p < 0.001), both fitted using a conventional fitting method. Treatment zone decentration was not significantly different between HiTor group I and II (p = 0.606). The magnitude of treatment zone decentration was positively correlated with the amount of baseline corneal toricity (LoTor and HiTor group I combined, p = 0.048). CONCLUSIONS: Eyes with higher amounts of corneal toricity give rise to increased amounts of treatment zone decentration in overnight orthokeratology.

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.

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.

Corneal versus ocular aberrations after overnight orthokeratology.

PURPOSE: To investigate relationships between changes to corneal and ocular aberrations induced by orthokeratology (OK) and their influence on visual function. METHODS: Eighteen subjects (aged 20 to 23 years) were fitted with OK lenses (BE Enterprises Pty Ltd, Australia), manufactured in Boston XO material (Bausch & Lomb Boston, Wilmington, MA), and worn overnight for seven nights. Corneal and ocular aberrations were simultaneously captured (Discovery, Innovative Visual Systems, Elmhurst, IL), and contrast sensitivity function was measured on days 1 and 7, within 2 and 8 hours after lens removal on waking. Data from the eye achieving the higher myopic correction were analyzed for changes over time. RESULTS: There was a significant refractive effect at all visits. Orthokeratology induced an increase in corneal and ocular root mean square higher order aberrations (HOAs) and a positive shift in spherical aberration (SA) on day 1, with further increases by day 7. Increases in root mean square coma became significant by day 7. Changes to corneal and ocular SA were similar on day 1; however, by day 7, there was a greater increase in corneal than ocular SA, indicating a change in internal SA. Orthokeratology led to an overall decrease in contrast sensitivity function, which was isolated to spatial frequency changes on day 1 at 1 cycle per degree and on day 7 at 1 and 8 cycles per degree. CONCLUSIONS: A greater positive shift in corneal compared with ocular SA on day 7 suggests a negative shift in internal SA, which would be consistent with an increased accommodative response. Lack of any difference on day 1 indicates that this may be an ocular adaptation response toward neutralizing induced positive SA, rather than a direct effect of SA changes on the accommodation mechanism.

Refractive changes from hyperopic orthokeratology monovision in presbyopes.

PURPOSE: To investigate the time course of refractive and corneal topographic changes in overnight hyperopic orthokeratology (OK) for emmetropic presbyopes. METHODS: Sixteen adult emmetropic presbyopic subjects were fitted with rigid hyperopic OK lenses (BE Enterprises, Brisbane, Australia/Capricornia, Slacks Creek, Australia) targeted to correct +2.00 D, in one eye only. The fellow eye acted as a non-lens-wearing control. Thirteen subjects completed the study. Lenses were worn overnight for a 7-day period, and changes in subjective refraction and corneal topography were measured in the morning on lens removal (A.M.) and 8 hr after lens removal (P.M.). RESULTS: There were statistically significant changes from baseline in all variables at all visits in lens-wearing eyes. Hyperopic OK caused a -1.00 (0.33) D shift in best vision sphere refraction at Day1 A.M., and -1.11 (0.61) D, at Day7 A.M., with -0.91 D of best vision sphere change from baseline still apparent by Day7 P.M. (mean [SD]). This led to an improvement in monocular near visual acuity (VA) from Jaeger 10.8 (2.4) at baseline to Jaeger 4.6 (2.5) at Day1 A.M., Jaeger 3.2 (2.3) at Day7 A.M., and Jaeger 3.9 (3.0) at Day7 P.M. Binocular distance VA did not change from baseline. The central cornea steepened, and the mid-peripheral nasal cornea flattened at lens removal after one night of wear. There was no significant difference in central corneal steepening between A.M. visits, but there was longer retention of effect by Day7 P.M. Nasal paracentral corneal flattening also showed a greater effect and longer retention of effect by Day7. CONCLUSIONS: Hyperopic OK induced central corneal steepening and paracentral corneal flattening, which led to a monovision myopic shift in refraction that was sufficient to provide functional correction of near vision. Lack of change in binocular distance VA indicates that hyperopic OK offers a viable option for providing monovision correction in emmetropic presbyopia.

Posterior corneal shape changes in myopic overnight orthokeratology.

PURPOSE: To evaluate changes in the shape of the posterior cornea at the end of the day based on anterior corneal topography and corneal thickness during myopic overnight orthokeratology (OK) over 14 nights' wear of reverse geometry gas-permeable (GP) contact lenses. METHODS: Eighteen subjects (aged 19 to 32 years) with low myopia and astigmatism were fitted with reverse geometry lenses (BE; Capricornia Contact Lens Pty Ltd) for myopic OK, which were worn overnight only for a 14-day period. A separate group of 10 subjects (aged 19 to 32 years) with low astigmatism wore J-Contour conventional GP lenses (Capricornia Contact Lens Pty Ltd) for one night. Corneal topography (Medmont E-300) and total corneal thickness (Holden-Payor optical pachometer) across the horizontal meridian were measured at baseline and approximately 8 to 10 hours after lens removal on days 1, 4, 7, and 14 of overnight OK lens wear and after one night of GP lens wear for the control group. Posterior corneal apical radius of curvature and asphericity (Q) were calculated using an in-house program based on the anterior corneal ellipse curve and corneal thickness. RESULTS: Myopia reduced from -2.64 ± 0.99 diopters (mean ± SD) to -0.39 ± 0.49 diopters during 14 days of overnight OK lens wear. In the OK lens-wearing eyes, there were no statistically significant changes in posterior corneal apical radius of curvature during 14 days of overnight OK. However, there were statistically significant increases in posterior corneal Q on days 4 and 7. In the conventional GP lens-wearing eyes, there were no statistically significant changes in either posterior corneal apical radius or Q after overnight lens wear. CONCLUSIONS: The results of this study support the current hypothesis that the OK refractive effect is achieved primarily through remodeling of the anterior corneal layers, without overall corneal bending.

Ocular aberrations and visual function with multifocal versus single vision soft contact lenses.

PURPOSE: To investigate differences in ocular aberrations induced by centre-near multifocal soft contact lenses (SCL) relative to single vision SCLs and their effect on contrast sensitivity function (CSF). METHODS: Ocular aberrometry was measured in 18 cyclopleged subjects (19-24 years) while wearing Ciba Air Optix low (AOlow) and high (AOhigh) add, Bausch & Lomb PureVision low (PVlow) and high (PVhigh) add multifocals, and a Bausch & Lomb PureVision single vision (PVsv) control with the same -3.00 D distance back vertex power. Zernike polynomials were scaled to 4, 5 and 6 mm pupils. CSF was measured at equivalent distances of 6 m, 1 m and 40 cm while fully corrected with spherical trial lenses at 6m. RESULTS: AOlow, AOhigh and PVhigh induced a negative shift in primary spherical aberration (Z12) from PVsv and all multifocal SCLs induced a positive shift in secondary spherical aberration (Z24) (all p<0.01), without significantly increasing coma. Area under the CSF (AUCSF) reduced at 40 cm for all multifocals relative to PVsv (p<0.05), but was not significantly different at 6 m or 1 m. A moderate correlation (r = -0.80, p<0.005) was found between changes in Z12 and AUCSF at 40 cm for AOhigh, with an increase in negative Z12 reducing multifocal-induced loss of CSF. CONCLUSIONS: Centre-near multifocal SCLs induced a negative shift in Z12 and a positive shift in Z24. Although CSF was unaffected at 6 m and 1m it was reduced at 40 cm, possibly because changes in Z12 and Z24 were not great enough to induce a significant shift in centre of focus and increase in depth of field.

Repeatability of internal aberrometry with a new simultaneous capture aberrometer/corneal topographer.

PURPOSE: To compare repeatability of internal eye aberrations derived from aberrometry and corneal topography (CT) measured simultaneously by the Innovative Visual Systems Discovery, against time displaced but same instrument measurement (Nidek OPD-Scan 3), and time displaced different instrument measurement (Medmont E300 and Imagine Eyes irx3). METHODS: Three aberrometry and CT measurements were captured with each instrument, except for the OPD-Scan 3 where three aberrometry scans were followed by a single CT. Measurements were repeated across 2 days. Corneal surface Zernike coefficients were derived from CT and subtracted from aberrometry to establish internal aberration coefficients. For the OPD-Scan 3, internal Zernike coefficients were derived by the instrument's software. Repeatability for second-order root mean square (RMS), spherical aberration, coma RMS, trefoil RMS, and the refraction components M, J0, and J45 were assessed using intraclass correlation coefficient (ICC). RESULTS: Intrasession repeatability was similar between the Discovery and E300/irx3, with the E300/irx3 slightly more repeatable for second-order RMS. Across days, the Discovery was most repeatable for second-order RMS (ICC 0.98) followed by the E300/irx3 (ICC 0.96) and OPD-Scan 3 (ICC 0.88). All instruments were less repeatable for higher order aberrations with only the Discovery moderately repeatable for spherical aberration and trefoil RMS (both ICC ≥ 0.75). The Discovery was highly repeatable for all derived refractive components (ICC ≥ 0.96). The E300/irx3 was highly repeatable for M (ICC 0.98) and moderately repeatable for J0 (ICC 0.89). The OPD-Scan 3 was highly repeatable for the M component (ICC 0.98) but not repeatable for the cylindrical components. CONCLUSIONS: The Discovery was highly repeatable for second-order RMS and derived refractive components. The lower repeatability for internal higher order aberrations measured with all instruments suggests caution in their use until further work is carried out to investigate sources of error and to develop methods to improve repeatability.

Mapping the corneal sub-basal nerve plexus in orthokeratology lens wear using in vivo laser scanning confocal microscopy.

PURPOSE: This study was designed to map the sub-basal nerve plexus (SBNP) in the cornea of orthokeratology (OK) lens wearers. METHODS: Laser scanning confocal microscopy (LSCM) was performed in vivo on three subjects: a non-lens wearer and two OK lens wearers. Scans were performed on the right eye while the left eye fixated a moving target. A total of 575, 430, and 676 contiguous images of the SBNP were taken from the non-lens wearing and the OK lens wearing subjects, respectively, and used to construct maps of the central to mid-peripheral SBNP. RESULTS: In the non-lens wearing eye, nerves radiated towards a whorl-like complex centered nasally and inferiorly in an overall pattern consistent with previously reported studies. In the OK lens wearing eyes, this whorl pattern was absent, replaced by a tortuous network of nerve fibers centrally, and thicker curvilinear fibers mid-peripherally, particularly in the nasal, inferior, and temporal regions. CONCLUSIONS: This study maps the corneal SBNP in OK lens wearers and provides compelling evidence that OK lens wear alters the normal SBNP distribution observed in healthy, non-lens wearing eyes.

Corneal thickness changes in hyperopic orthokeratology measured by optical pachometry.

PURPOSE: To investigate the time course of corneal thickness changes in overnight hyperopic orthokeratology (OK) lens wear for a 4-day lens-wearing period. METHODS: Fourteen subjects (age range, 20-37 years) were fitted with hyperopic OK lenses in one eye only. The fellow eye acted as a non-lens wearing control. Lenses were worn overnight only for 4 nights, and changes from baseline in subjective refraction, corneal topography, and corneal thickness (Holden-Payor optical pachometer) at central and para-central locations were measured on days 1 and 4 after overnight lens wear, at lens removal (AM), and 8 hours after lens removal (PM). RESULTS: There was a significant refractive and corneal topographic effect at all visits. The central total cornea thickened significantly at AM visits only because of significant stromal thickening consistent with the overnight lens wearing edema response, and returned to baseline at PM visits once edema resolved. The para-central epithelium significantly thinned at all AM and PM visits. This counteracted para-central stromal thickening at AM and resulted in significant thinning of the total para-central cornea at PM visits when stromal thickness had returned to baseline. CONCLUSIONS: Para-central corneal epithelial thinning explains corneal anterior surface steepening in hyperopic OK and is sufficient to account for the lens-induced refractive response. Whereas corneal thickening is an additional factor reported in myopic OK, this was not the case in hyperopic OK. Constraint of corneal surface change mechanisms to para-central corneal epithelial thinning alone in hyperopic OK may explain the reduced refractive effect compared with myopic OK.

Lens Dk/t influences the clinical response in overnight orthokeratology.

PURPOSE: To investigate the influence of lens oxygen transmissibility (Dk/t) on the clinical response to overnight (ON) orthokeratology (OK) lens wear over 2 weeks. METHODS: Eleven subjects (age, 20 to 39 years) were fitted with OK lenses (BE; Capricornia Contact Lens) in both eyes. Lenses in matched design/fitting but different materials (Boston EO and XO; nominal Dk/t: 26 and 46 ISO Fatt, respectively) were worn ON only in the two eyes over a 2-week period. Changes in logarithm of the minimum angle of resolution visual acuity, subjective refraction (spherical equivalent), corneal apical radius ro and asphericity Q (Medmont E300), and central stromal thickness (Holden-Payor optical pachometer) were measured. RESULTS: There were statistically significant differences in outcomes between the two lens materials (analysis of variance, p < 0.001) throughout the study. After 2 weeks of ON OK lens wear, changes from baseline (mean ± standard deviation) with the EO lenses were significantly less than XO for visual acuity (-0.72 ± 0.37 vs. -0.83 ± 0.41; p = 0.012), refraction [+2.19 ± 0.73 diopter (D) vs. +2.74 ± 0.70 D; p = 0.004], ro (0.34 ± 0.08 mm vs. 0.46 ± 0.11 mm; p < 0.001), and Q (0.26 ± 0.08 vs. 0.36 ± 0.08; p < 0.001). After the first ON OK lens wear, change in central stromal thickness was greater for EO compared with XO (27 ± 36 µm vs. 10 ± 31 µm; p = 0.05), but ON edema was reduced after 2 weeks for both lens materials (8 ± 25 µm vs. -1 ± 33 µm; p > 0.05). CONCLUSIONS: An increase in lens Dk/t appears to increase the clinical effects of ON reverse-geometry lens wear over the medium term. This adds further support to the recommendation that high Dk materials should be used for ON OK not only to provide physiological advantages but also to optimize clinical outcomes.

Residual corneal flattening after discontinuation of long-term orthokeratology lens wear in asian children.

OBJECTIVES: Most patients treated with orthokeratology (OK) in Asia are children. The effects of long-term OK on corneal curvature among children after lens wear discontinuation have not previously been reported. METHODS: This study investigated 28 subjects, aged 10.4 +/- 2.5 years at commencement of OK lens wear, who had been treated with OK for 50.2 +/- 27.4 months. Corneal curvature was measured with a Canon RK3 autokeratometer before commencement of OK and again approximately 2 weeks (17.3 +/- 8.6 days) after discontinuation of OK lens wear. Data were analyzed using paired Student t tests, with a critical P value of 0.05. RESULTS: Compared with baseline, residual flattening of the cornea was found after cessation of OK lens wear, averaging 0.07 +/- 0.04 mm in the flat meridian (P<0.001) and 0.02 +/- 0.07 mm in the steep meridian (P=0.07). This was confirmed by power vector analysis of curvature data, with a significant reduction in M (-0.27 +/- 0.23 diopter (D); P<0.001), and a slight increase in J0 (0.17D +/- 0.36D; P=0.02). A trend toward greater residual corneal flattening was found among subjects with more pretreatment myopic refractive error (P=0.04). CONCLUSIONS: Corneal curvature may not necessarily return completely to baseline after discontinuation of long-term OK lens wear in children. Intermittent temporary discontinuation of OK lens wear and close monitoring of corneal recovery are recommended during long-term OK treatment.

The effect of treatment zone diameter in hyperopic orthokeratology.

PURPOSE: To investigate the time course of treatment zone (TZ) diameter changes in hyperopic orthokeratology (OK) lens wear from 1 h in the open eye through to seven nights in the closed eye. METHODS: Twelve subjects were fitted with rigid hyperopic OK lenses. Lenses were worn in the open eye for 1 h then one night in the closed eye, separated by a washout period of 4 days. Changes in best corrected visual acuity (BCVA) and corneal topography (Medmont E-300) were measured on lens removal. The TZ, comprising the central steepened zone (CSZ) and surrounding annular flattened zone (AFZ), was measured from corneal topography. Subsequently, ten subjects wore the same lens design overnight for seven nights, and measurements were taken on lens removal and 8 h later on Days 1 and 7. RESULTS: Both CSZ and AFZ were apparent after 1 h of hyperopic OK lens wear. CSZ decreased while AFZ increased with longer periods of lens wear. BCVA reduced with longer periods of lens wear and was associated with decreasing CSZ (r = -0.866, p < 0.001) and increasing AFZ (r = 0.447, p < 0.05). CONCLUSIONS: The association of changes of treatment zone size with reductions in BCVA suggests that increasing CSZ may lead to better visual outcomes in hyperopic OK.

Mechanism for corneal reshaping in hyperopic orthokeratology.

PURPOSE: To investigate the mechanism underlying hyperopic orthokeratology (OK) by comparing the short-term clinical effect of lenses before and after central lens fenestration. METHODS: Twelve subjects (age 21 to 24 years) were fitted with rigid hyperopic OK lenses (BE Enterprises/Capricornia) in one eye only. The fellow eye acted as a non-lens wearing control. Lens specifications were matched to provide the same post lens tear film profile in all subjects. Non-fenestrated lenses were worn in the open eye for 1 h and in the closed eye for four nights. Subjective spherical equivalent refraction and corneal topography (Medmont E300) were measured at baseline, after 1 h of lens wear, and within 1 h of waking on days 1 and 4 of overnight lens wear. The lenses were then sent for three 0.75 mm fenestrations within the central optic zone, and lens wearing and measurement procedures were repeated. RESULTS: There was a statistically significant change from baseline in all variables at all visits in lens wearing eyes. Refraction changed after 1 h of lens wear, with greater effect after overnight wear. Para-central corneal flattening was apparent after 1 h of lens wear, with greater flattening after overnight wear. Central corneal steepening was only statistically significant after overnight wear. Central fenestrations did not lead to a difference in clinical effect in any variables. However, a correlation between apical corneal curvature change and refractive change became apparent only after lens fenestration. CONCLUSION: A hyperopic OK effect was established after 1 h with increased effect with longer lens wearing time. Central fenestrations did not affect the clinical outcomes, indicating that corneal compression by the lens in the para-central region as opposed to central post lens tear film suction may be the primary mechanism behind the hyperopic OK clinical effect.