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T. Hiraoka, Y. Kaji, F. Okamoto, T. Oshika; Corneal Sensation After Overnight Orthokeratology. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5625.
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It is well known that contact lens wear causes loss of corneal sensation regardless of the lens material and wearing modality. However, little is known about the influence of overnight orthokeratology on corneal sensation. Therefore, we conducted this prospective study to assess corneal sensation before and after overnight orthokeratology.
Thirty-four eyes of 17 patients undergoing overnight orthokeratology were enrolled in this study. Their age 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 commencement of the treatment, and each eye was tested at five different corneal locations: one central point and four peripheral points at the superior, inferior, temporal and nasal positions 2 mm away from the limbus.
Overnight orthokeratology significantly reduced corneal sensation from 58.24 ± 6.14 mm at baseline to 49.12 ± 13.90 mm at 3 months after commencement of the 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 at 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).
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.
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