Posterior corneal changes with orthokeratology

Purpose. To investigate changes in corneal thickness and the radius of curvature of the posterior corneal surface after orthokeratology (OK) rigid lens wear. Methods. Nineteen young myopic subjects wore reverse-geometry OK lenses (BE/ABE, Ultravision Contact Lenses, Brisbane, Australia) every night for 1 month. Central and midperipheral corneal thickness (Allergan Humphrey ultrasound, Carl Zeiss Meditec, Dublin, CA), topography (EyeSys v.3.1, Houston, TX), subjective refraction, and posterior corneal radii (video photography of Purkinje images) were evaluated within 2 h of waking, prelens wear, and on four occasions postlens wear during a 1-month period. A mixed-models approach was used to analyze the data. We modeled the changes in posterior corneal radius of curvature and corneal thickness in terms of the sagittal height of the anterior and posterior cornea using an ellipsoidal model for the corneal surfaces. Results. Refractive error reduced from -2.28 to -0.01 DS within 1 month. A significant thinning of the cornea was evident between 1 (p = 0.03) and 2 weeks (p = 0.0048) postlens wear. A significant increase in the anterior corneal radius of curvature was present at all time periods beyond I night (p < 0.001), and a significant posterior corneal flattening occurred centrally and midperipherally after 1 week (p = 0.04 and p = 0.013, respectively). Conclusions. These findings suggest that in addition to the significant topographic flattening of the anterior corneal surfaces, there is also a significant flattening of the posterior surface during the early adaptive stages of OK lens wear.