Purpose: To compare keratocyte density, stromal backscatter, epithelial thickness, and corneal sensitivity between corneas of long-term contact lens wearers and those of non-contact lens wearers.
Methods: Twenty corneas of 20 daily contact lens wearers (>10 years' duration) and 20 corneas of 20 age-matched (+/-5 years) control subjects who had never worn contact lenses, were examined by confocal microscopy in vivo. The contact lens wearers removed their lenses 12 to 24 hours before the examination. Full-thickness images were recorded from the central and temporal cornea, and bright objects (keratocyte nuclei) in images were manually counted to calculate keratocyte density. Stromal intensity (backscatter) was measured by calculating the mean grayscale value (corrected for camera and light source variations) from the center of stromal images. Epithelial thickness was determined from the distance between images of the surface epithelium and subbasal nerve plexus. Central corneal sensitivity was measured by Cochet-Bonnet esthesiometry and correlated with the number of nerve fiber bundles in the subbasal nerve plexus.
Results: Full-thickness central and temporal keratocyte densities in contact lens wearers were 22,122 +/- 2,676 cells/mm(3) (mean +/- SD) and 20,731 +/- 2,627 cells/mm(3), respectively, and were not significantly different from central and temporal keratocyte densities in control subjects (P = 0.29). The minimum detectable difference in cell density was 11% (2346 cells/mm(3) and 2235 cells/mm(3) in central and temporal stroma, respectively). Temporal epithelial thickness was 46.3 +/- 4.7 microm in contact lens wearers and 50.9 +/- 4.7 microm in control subjects (P = 0.02). Central epithelial thickness and stromal backscatter did not differ between contact lens wearers and control subjects (P > 0.05). Corneal sensitivity was lower in contact lens wearers than it was in control subjects (P = 0.05) and did not correlate with the number of nerve fiber bundles in the subbasal nerve plexus.
Conclusions: Long-term daily contact lens wear and its associated stromal hypoxia and acidosis have no demonstrable effect on keratocyte density. The temporal epithelium is thinner in corneas of long-term contact lens wearers than in control subjects. Decreased corneal sensitivity in contact lens wearers is not accompanied by decreased nerve fiber bundle density.