Retention and regression of orthokeratology with time

Abstract

The exact changes that occur with accelerated orthokeratology over time have not been fully described to date. This paper attempts to answer the questions of the degree of retention and regression of the effect over a period of 8 to 9 hours post-wear. A retrospective study of 48 patients who had undergone orthokeratology for the correction of mild to moderate myopia was performed, with the subjects presenting for review at intervals of approximately 7, 30 and 90 days. The lenses had been worn overnight for a mean time of 9.27 ± 0.38 hours, with a mean post-wear interval of 8.52 ± 0.57 hours between initial and final assessment. A paired student t-test was used to compare the post-wear apical corneal power (ACP) changes and the retention of the induced effect over the period of time. The regression of the orthokeratology effect was analyzed by non-parametric means (chi-square analysis) due to the non-normal distribution of the results. The change in apical corneal power showed a statistically significant difference between 7 and 30 days ( p = 0.014), 7 and 90 days ( p = 0.0002), and a lower significance at 30 vs 90 days ( p = 0.06). Retention of the effect was also significant for 7 vs 30 days ( p = 0.001) and 7 vs 90 days ( p < 0.0001), but less so for 30 vs 90 days ( p = 0.06). Regression for degrees of 0.75 D or less showed variances in significance (chi-square) of 7 vs 30 ( p = 0.08), 7 vs 90 ( p = 0.003) and 30 vs 90 ( p = 0.026). For changes of 0.50 D or less regression, the results were 7 vs 30 ( p = 0.12), 7 vs 90 ( p = 0.0012) and 30 vs 90 ( p = 0.06). The results indicate that the major change in refraction occurs within the first 30 days, and that there is a significant increase in the degree of retention over the first 90 days of treatment. This is reflected in the degree of regression, which appears to stabilize between 0.50 to 0.75 D per day, by the 90-day period. The effects of regression should be taken into account prior to initiating a course of treatment with orthokeratology.