Purpose.
To investigate the mechanism of the refractive effect of orthokeratology by using measurements of the anterior and posterior radii of the corneal curvature and anterior chamber depth with a Pentacam analysis system.
Methods.
Nine women (18 eyes) with a mean age of 29.6 ± 3.8 years and low to moderate myopia (≤–4.00 diopters [D]) were recruited for a 53-week trial of overnight orthokeratology using RD171K lenses (hexafocon A). After wearing the orthokeratology lenses overnight, subjects were examined during the day. With a Pentacam analysis system, subjects were examined at 2, 4, 8, 12, 24, 36, and 53 weeks for the assessment of the anterior and posterior radii of the corneal curvature and anterior chamber depth.
Results.
Myopic refractive error significantly reduced during the trial (P<0.001, analysis of variance). The mean refractive error was –2.85 ± 0.46 D at baseline and significantly reduced to –0.28 ± 0.65 D at 2 weeks (P<0.01, Bonferroni–Dunn post hoc test). At any week, no significant differences were seen in the central posterior radius of the corneal curvature (P=0.55, analysis of variance) or the anterior chamber depth (P=0.69, analysis of variance). The amount of change in the central anterior radius of the corneal curvature significantly correlated with the change in refractive error at 24 weeks (r = 0.57, P<0.05, Pearson correlation coefficient).
Conclusions.
Overnight orthokeratology lens wear alters the anterior corneal shape rather than the posterior radius of the corneal curvature and the anterior chamber depth. This finding suggests that the primary factor in the refractive effect of orthokeratology is change in the anterior corneal shape rather than overall corneal bending.
