Malleability of the Ocular Surface in Response to Mechanical Stress Induced by Orthokeratology Contact Lenses

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Abstract
To determine the malleability of the ocular surface by examining the acute effects of local mechanical stress on optical performance, corneal shape, and corneal/epithelial thickness after corneal refractive therapy for myopia and hyperopia (CRT and CRTH). Twenty ametropes (spherical equivalent: -2.08 +/- 2.31 D) wore CRT and CRTH lenses in a random order on 1 eye (randomly selected). The lenses were worn for 15, 30, and 60 minutes (randomly ordered, with each period taking place on a different day). Refractive error, aberrations, corneal topography, and corneal/epithelial thickness (using OCT) were measured before and after lens wear. The measurements were performed on the control eyes at the 60-minute visit only. With both CRT and CRTH lens wear, significant changes occurred in many parameters from the 15-minute time point. The refractive error and defocus decreased after CRT lens wear (all P < 0.05) and increased after CRTH lens wear from baseline (all P < 0.05). Astigmatism did not change (both P > 0.05). Higher-order aberrations, including coma and spherical aberration (SA), increased after CRT and CRTH lens wear (all P < 0.05) from baseline, but the signed SA shifted from positive to negative after CRTH lens wear (P < 0.05). The central cornea flattened and the midperiphery steepened after CRT lens wear, whereas the central cornea steepened and paracentral region flattened after CRTH lens wear (P < 0.05). The central cornea swelled less than the midperiphery after CRT lens wear (P < 0.05), whereas the central cornea swelled more than the paracentral region after CRTH lens wear (P < 0.05). The central epithelium was thinner than the midperiphery after CRT lens wear (P < 0.05) and thicker than the paracentral region after CRTH lens wear (P < 0.05). Optical performance, corneal curvature, and epithelial thickness did not change from baseline in the control eyes (all P > 0.05). CRT lenses for myopia and hyperopia induce significant structural and optical changes in as little as 15 minutes. The cornea, particularly the epithelium, is remarkably malleable, with rapid steepening and flattening possible in little time.