Abstract
Purpose. Quantifying adaptation to light distortion of subjects undergoing orthokeratology (OK) for myopia during the first month of treatment. Methods. Twenty-nine healthy volunteers (age: 22.34 ± 8.08 years) with mean spherical equivalent refractive error −2.10 ± 0.93D were evaluated at baseline and days 1, 7, 15, and 30 of OK treatment. Light distortion was determined using an experimental prototype. Corneal aberrations were derived from corneal topography for different pupil sizes. Contrast sensitivity function (CSF) was analyzed for frequencies of 1.50, 2.12, 3.00, 4.24, 6.00, 8.49, 12.00, 16.97, and 24.00 cpd under photopic conditions. Results. Average monocular values of all light distortion parameters measured increased significantly on day 1, returning to baseline after 1 week (P < 0.05 in all cases). Spherical-like aberration stabilized on day 7 for all pupil diameters, while coma-like for smaller pupils only. CSF was significantly reduced on day 1 for all spatial frequencies except for 1.5 cpd, returning to baseline afterwards. Significant correlation was found between light distortion and contrast sensitivity for middle and high frequencies (P < 0.05) after 15 days. Conclusion. Despite consistently increased levels of corneal aberrations, light distortion tends to return to baseline after one week of treatment, suggesting that neural adaptation is capable of overcoming optical quality degradation.
Highlights
Modern corneal refractive therapy (CRT) or orthokeratology (OK) aims to reshape the anterior corneal surface by the overnight application of reverse geometry contact lenses (CL)
It is assumed that the increase in corneal higher order aberrations and related optical quality degradation will remain during the treatment [11]; we hypothesize that the increase in light distortion phenomena is a transient process that might be independent of the optical quality changes in the corneal surface and might have an impact on visual quality
Size-related light distortion parameters (LDI and Best Fit Circle Radius (BFCr)) and regularity-related parameters (BFCirr and BFCsd) showed a statistically significant change over time on ANOVA analysis (P < 0.05) but there were no significant changes from baseline to any of the subsequent analyses (Bonferroni correction for multiple comparisons)
Summary
Modern corneal refractive therapy (CRT) or orthokeratology (OK) aims to reshape the anterior corneal surface by the overnight application of reverse geometry contact lenses (CL). In the case of myopia correction, the central cornea is flattened to achieve the desired reduction in the power of the anterior corneal surface, while the midperipheral cornea steepens [1, 2] as a result of the epithelial thickness redistribution from the corneal center These histological modifications occurring in orthokeratology [3, 4] drive a change in the optical quality of the cornea, significantly increasing spherical aberration in the positive direction [5, 6] with an impact on visual quality, under low luminance conditions [7,8,9]. It is assumed that the increase in corneal higher order aberrations and related optical quality degradation will remain during the treatment [11]; we hypothesize that the increase in light distortion phenomena is a transient process that might be independent of the optical quality changes in the corneal surface and might have an impact on visual quality
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