CORNEAL RESPONSE TO ORTHOKERATOLOGY

Purpose. The technique of orthokeratology produces a corneal response to the mechanical pressures exerted by rigid contact lenses. This pape r reports a study which investigated the topographic and pachometric c orneal changes induced by orthokeratology, Methods. Six young myopic s ubjects (11 eyes) wore ''accelerated orthokeratology'' lenses (OK-74; Center Inc., Sherman Oaks, CA) in a high Dk material (AirPerm; Dk = 88 ) for 28 days. Corneal and epithelial thickness were measured topograp hically using the Holden-Payor optical micropachometer, and corneal to pography was monitored using the EyeSys system. Results. Refractive er ror change reached 1.71 +/- 0.59 D reduction in myopia after 28 days. After 1 day of lens wear, statistically significant central corneal fl attening was noted, which progressed to reach 0.22 +/- 0.07 mm (1.19 /- 0.38 D) at 28 days. A trend toward central epithelial thinning was apparent, reaching statistical significance on day 28 (7.1 +/- 7.1 mu m; 9.6%). Midperipheral corneal thickening was also found approximatel y 2.5 mm from the corneal center, which was statistically significant by day 14 (13.0 +/- 11.1 mu m; 2.4%). Calculations using Munnerlyn's f ormula indicate that changes in corneal sagittal height based on topog raphical thickness changes across the flattened central 5.25-mm zone c an account for the refractive changes observed. Conclusions. These fin dings suggest that the initial corneal response to orthokeratology may be explained by redistribution of corneal tissue, rather than by over all bending of the cornea.