Effects of hypoxia on corneal epithelial permeability

PURPOSE: Epithelial permeability to fluorescein (P-dc) increases with close d eye soft contact lens wear. Possible mechanisms responsible for this chan ge include corneal hypoxia land acidosis) during overnight wear and interfe rence of the lens with normal tear exchange. In this study we used a local environmental chamber to examine the effects of hypoxia on P-dc. METHODS: After baseline slit-lamp examination, autofluorescence, and centra l corneal thickness measurements, 35 subjects were fitted with a pair of ai rtight swimming goggles. One eye was exposed to a humidified gas mixture co ntaining 95% nitrogen (N-2) and 5% carbon dioxide (CO2), and the fellow (co ntrol) eye was exposed to air. The experimental eye and the eye measured fi rst were assigned using a randomized block design. After the subjects wore the goggles for 1 hour, corneal thickness measurements were repeated and P- dc was assessed as previously described. A final slit-lamp examination was performed by a masked examiner to assess epithelial integrity. RESULTS: There was no significant difference in the mean In(P-dc) (95% conf idence interval) for eyes exposed to N-2/CO2 when compared with paired eyes exposed to air (-2.70 [-2.99, -2.41] vs -2.51 [-2.72, -2.30] ln[nm/sec], P = .272). Although there was also no substantial difference in the slit lam p appearance of the experimental and control eyes, the mean (95% confidence interval) change in corneal thickness for the hypoxic eyes was 19.78 (15.7 2, 23.84) mu m compared with 3.40 (-0.67, 7.47) mu m (P < .0001) in the con trol eyes. CONCLUSION: One hour of hypoxia caused a significant increase in corneal th ickness with no apparent change in P-dc. This suggests that other factors, either alone or in combination with hypoxia, may be responsible for increas ed P-dc during closed-eye contact lens wear. (Am J Ophthalmol 1999;127:153- 157, (C) 1999 by Elsevier Science Inc. All rights reserved.)