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.)