Corneal swelling at low atmospheric oxygen pressures.

Corneas of 28 human subjects were exposed to oxygen partial pressures, in a gas goggle, of either 6.9, 17.1, or 22.2 mm Hg, and the corneal swelling was measured by pachometry for 4 hr. Following an initial rise, the swelling stabilized after about 3 hr; in many subjects it was reversed, indicating an adaptation process. The average corneal swelling after 4 hr for the three oxygen partial pressures was 5.07%, 2.13%, and 1.66%, respectively. The average minimum oxygen requirement to prevent corneal swelling was at least 23 mm Hg and varied significantly among individuals. The variations in swelling responses were large enough to explain clinical differences in edema of patients wearing oxygen-permeable contact lenses, in the absence of adequate tear pumping.