Human corneal oxygen demands at superior, central, and inferior sites

Oxygen depletion of the superior and central cornea in response to standard conditions is of clinical interest because of pathological conditions, usually resulting from the hypoxia of contact lens wear, that affect these areas. A study was designed to determine if there are differences in oxygen depletion at these two sites.

Oxygen depletion times from a standard reservoir following corneal exposure to three different oxygenated environments (20.9%, 5%, and 0% oxygen) were assessed micropolarographically at central, superior, and inferior corneal surface positions on both corneas of six healthy young adult human subjects.

Based on 48 measurements for each corneal position at each oxygen percentage (432 total measurements), the superior cornea 1.0 mm from the limbus was found to have longer oxygen depletion times (slower oxygen uptake rates) than the central or inferior corneal locations. The differences reduced to nearly zero during the course of the initial 1.5-day testing procedure, but were re-established months later when testing was resumed.

There is a small reversible increase in superior corneal oxygen depletion time (a decrease of the oxygen uptake rate) due to the chronic hypoxia that results from the presence of an overlying superior eyelid or other physiological factors.