The minimum precorneal oxygen tension to avoid corneal edema.

One eye of each of eight subjects was exposed to gases containing oxygen concentrations of 1.0%, 2.5%, 4.9%, 7.5%, 10.1%, and 21.4% (oxygen partial pressures ranging from 8 to 158 mmHg) for 8 hr. The precorneal oxygen concentration required to avoid corneal edema for the group as a whole was 10.1% (an oxygen tension of 74 mmHg). There was considerable individual variation both in the corneal swelling response with each of the various oxygen concentrations and in the atmospheric oxygen concentration required to avoid edema: one subject required 7.5%, four subjects required 10.1%, and three subjects required 21.4% oxygen concentration. The results of this study suggest that the cornea requires higher levels of atmospheric oxygen than previously considered necessary for normal function.