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.