This figure displays the effects of one hour of eye closure with and without contact lens. Log permeability measurements for each control and contact lens eye are shown. The mean difference in ln(Pdc) between the paired experimental and control eyes was 0.341 ln(nm/sec) (95% CI: 0.069, 0.613) (p=0.016; two-sided t-test). This difference corresponds to an average increase in permeability of 41% for eyes exposed to only one hour of contact lens-induced hypoxia compared to the contralateral eyes that were closed for one hour without CLs. Interestingly, this mild corneal trauma typically did not produce a detectable difference between paired-eyes in either slit-lamp or corneal thickness measurements. Following one hour of eye closure, all eyes were free of epithelial disruption, and the mean absolute change in corneal thickness (DCT = postlens CT - prelens CT) was 12.2 µm (95% Confidence Interval: 9.5, 15.0) in the contact lens-wearing eyes and 14.5 µm (95% CI: 10.9, 18.2) in the control non-lens-wearing eyes. The mean difference in absolute corneal swelling between paired eyes (experimental eye - control eye) was -2.3 µm (95% CI: -7.5, 2.9), which is neither clinically nor statistically significantly different from zero (p=0.37). McNamara N, Fusaro R, Brand R, Polse K. Epithelial permeability reflects subclinical effects of contact lens wear. Brit J Ophthalmol 1997; In press.