Posterior corneal curvature change and recovery after 6 months of overnight orthokeratology treatment

Purpose: To investigate the changes in, and recovery of, posterior corneal curvature after 6 months of overnight orthokeratology (ortho‐k). Methods: Twenty‐eight healthy young adults were recruited for a 6‐month period of ortho‐k treatment and data from their right eyes were analyzed. The mean ± standard deviation spherical equivalent refraction (SER) at baseline was ?2.95 ± 0.88 D. Posterior simulated keratometry (Sim K) readings were measured with a corneal topographer based on rotating Scheimpflug imaging. The three phases in the study were the 6‐month treatment period (Phase I); diurnal changes over a period of 8 h immediately after lens removal at the completion of the treatment period (Phase II); and a 2‐month recovery period after cessation of treatment (Phase III). Measurements were taken after lens wear overnight, and after 1 week, and 1, 2, 3 and 6 months of lens wear in Phase I. In Phase II, measurements were taken immediately, and then 2, 4 and 8 h after lens removal. In Phase III, corneal parameters were monitored 1 week, 2 weeks, 1 month and 2 months after cessation of ortho‐k treatment. Results: In Phase I, the posterior Sim K readings were significantly steepened after the first overnight lens wear. These significant changes were not found at other visits. In Phase II, the posterior Sim K readings were the steepest immediately after lens removal and significantly flattened 2 h after lens removal. In Phase III, all the posterior Sim K readings were similar to the baseline results. Conclusions: Steepening of the posterior cornea was only observed immediately after lens removal. It returns to its original shape within 2 h after cessation of lens wear. These changes appear to be in line with recent reports of the diurnal variation in the posterior corneal shape in non‐contact lens wearers. The reduction in myopia from ortho‐k treatment is therefore mainly due to a flattening of the anterior cornea.