Corneal Sensation After Overnight Orthokeratology

Purpose: The purpose of this study was to investigate the influence of overnight orthokeratology on corneal sensation. Methods: A prospective study was conducted in 34 eyes of 17 patients undergoing overnight orthokeratology. Their ages ranged from 21 to 33 years (23.5 +/- 3.2 years, mean standard deviation). The logarithm of minimum angle of resolution of uncorrected visual acuity at baseline ranged from 0.22 to 1.52 (0.71 +/- 0.32), and myopic refractive error ranged from -1.00 to -4.00 D (-2.15 +/- 0.90 D). Corneal sensation was measured using the Cochet-Bonnet esthesiometer before and 3 months after the start of treatment, and each eye was tested at 5 different corneal locations: one central point and 4 peripheral points at the superior, inferior, temporal, and nasal positions 2 turn away from the limbus. Results: Overnight orthokeratology significantly reduced corneal sensation from 58.24 +/- 6.14 mm at baseline to 49.12 +/- 13.90 mm at 3 months after the start of treatment at the central point (P = 0.0003, Wilcoxon signed-rank test), from 58.24 +/- 6.14 to 47.65 +/- 14.37 mm at the superior point (P = 0.0002), from 57.50 +/- 6.43 to 48.09 +/- 14.82 mm at the inferior point (P = 0.0004), from 58.24 +/- 6.14 to 50.44 +/- 13.73 mm at the temporal point (P = 0.0009), and from 57.65 +/- 6.54 to 48.68 +/- 14.84 mm at the nasal point (P = 0.0022). There were no significant differences in corneal sensation among these 5 points 3 months after the treatment (P = 0.9549, Kruskal-Wallis test). The induced change in corneal sensation at the central cornea was further analyzed in relation to the amount of myopic correction. There was no significant correlation between the loss of corneal sensation and the amount of myopic correction (r = -0.211, P = 0.2245, Spearman rank correlation). Conclusions: Overnight orthokeratology significantly reduced corneal sensation at both central and peripheral locations, and the reduction was not correlated with the amount of myopic correction. At present, the clinical significance of this sensory loss is not clear, but practitioners should take this effect into account in the practice of orthokeratology.