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.