Effect of overnight orthokeratology on corneal surface morphology and corneal aberrations

Objective To evaluate the changes of the corneal surface morphology and corneal aberrations undergoing overnight orthokeratology treatment and to assess the effect of the amount of decentration on corneal aberrations. Methods This was a prospective clinical study. Twenty-two patients with low and moderate myopia [(-2.23±0.74)D] aged (24.4±2.2)years were included and fitted with Ortho-K contact lenses (CL). The center refractive status was measured with an open field infrared refractometer (Grand Seiko 5500); corneal topography and the amount of decentration (including the magnitude and the orientation) were measured with Medmont E-300 Corneal Topographer, corneal topography data were converted into aberrations data by a Matlab software. The measurements were taken in fight eyes, at pre-wear, 7 days and 30 days after orthokeratology. Data were analyzed with a paired t test, an independent samples t test, an one-way ANOVA, or a Pearson correlation analysis. Results The myopia amount of all subjects were significantly reduced after Ortho-K CL wear within the first week. The reduction also happened in central corneal curvature. The average amount of decentration of 1 week was (0.49±0.24)mm, no more significant changes thereafter.The direction of decentration was mainly in the temporal side, followed by the bottom side. Root mean square (RMS) of corneal total higher-order aberrations, third-order aberration, fourth-order aberration were significantly increased compared to before wear and the changes were stabilized after 1 week. Corneal third-order aberrations variation correlated with decentration (r=0.492, P＜0.05); corneal fourth-order aberration variation did not show significant correlation with decentration; the combined coma variation significantly correlated with both orientation and magnitude of decentration (r=0.546, P＜0.05; r=0.710, P＜0.05). Initial higher astigmatism did not induce the greater amount of decentration. Conclusion Myopia amount reduction along with corresponding corneal curvature changes occurre mostly within 1 week after orthokeratogy; corneal total higher-order aberrations, third-order aberration and fourth-order aberration increase, the addition of coma relate to the decentration after orthokeratology; the decentration after orthokeratology do not relate to the initial astigmatism. Key words: Myopia;  Orthokeratologic procedures;  Decentration;  Aberrations