Corneal epithelial thinning profile induced by long-term wear of hydrogel lenses

Purpose. To characterize the epithelial thickness profile and study the effects of long-term wear of hydrogel lenses on this profile. Methods. A cross-sectional study was designed. Epithelial thickness was evaluated in 15 subjects who had worn one of two types of low oxygen transmissibility (Dk) hydrogel contact lenses for a average of 10 years (range, 7-16) and compared with a group of 18 control subjects who had never worn contact lenses. Epithelial thickness was measured at the center and at four mid-peripheral and four peripheral locations in the vertical and horizontal meridians of the cornea using a modified optical pachymeter. Results. Lens wearers had significantly thinner epithelium than controls [analysis of variance (ANOVA), p < 0.001] in the central (41 +/- 7 mu m versus 48 +/- 5 mu m), mid-peripheral (41 +/- 7 mu m versus 48 +/- 7 mu m), and peripheral (42 +/- 9 mu m versus 48 +/- 6 mu m) cornea. The extent of this difference ranged from 8.7% to 18.4% of the total epithelia] thickness, was not associated with the duration of wear (ANOVA, p = 0.87, power = 0.05), and was significantly greater for the lower Dk contact lens type (ANOVA, 1) < 0.001). Topographical position did not have a significant effect on epithelial thickness (ANOVA, p > 0.13, power > 0.22). Conclusion. This study establishes that the epithelial thinning associated with hydrogel lens wear is topographically uniform. It also confirms that this effect is inversely related to lens oxygen transmissibility but does not appear to increase with longer duration of wear.