Quantitative evaluation of regular and irregular corneal astigmatism in patients having overnight orthokeratology☆

Purpose: To quantitatively assess changes in regular and irregular corneal astigmatism in patients having overnight orthokeratology.

Setting: Matsumoto Eye Clinic, Ibaraki, Japan.

Methods: A prospective study was conducted of 64 eyes of 39 patients having overnight orthokeratology for myopia. Inclusion criteria were an uncorrected visual acuity (UCVA) of 20/20 or better after treatment and a minimum follow-up of 3 months. Using Fourier series harmonic analysis, videokeratography data were decomposed into spherical component, regular astigmatism, asymmetry (tilt or decentration), and higher-order irregularity.

Results: Orthokeratology significantly reduced the manifest refraction from −2.60 diopters (D) ± 1.13 (SD) to −0.17 ± 0.31 D (P<.0001, paired t test) and improved the UCVA from 0.82 ± 0.30 to −0.11 ± 0.06 logMAR (P<.0001). Regular astigmatism increased significantly from 0.53 ± 0.23 D preoperatively to 0.63 ± 0.40 D postoperatively (P = .0206). The asymmetry component increased significantly from 0.35 ± 0.22 D to 0.64 ± 0.40 D (P<.0001). Higher-order irregularity did not change significantly: 0.14 ± 0.11 D before treatment and 0.17 ± 0.20 D after treatment (P = .2166). The amount of myopic correction correlated significantly with the increase in the asymmetry component (Pearson correlation coefficient, R = 0.40, P = .0009) but not with the increase in regular astigmatism (R = 0.24, P = .055).

Conclusions: Irregular corneal astigmatism significantly increased, even in clinically successful orthokeratology cases. The effect of the changes on visual function should be studied further.