Critical oxygen requirements to avoid oedema of the central and peripheral cornea.

A randomized double-masked experiment was performed to compare the critical oxygen concentrations required to avoid corneal thickening at the central and peripheral cornea. Pachometry was performed on 10 subjects before and after 3 h of corneal exposure to the following gasmixtures: 0.00, 1.01, 2.65, 5.13 and 10.3% oxygen, balance nitrogen. Widely ranging critical values (from 4.4 to 11.6% for the central cornea and 1.7 to 15.8% for the peripheral cornea) could be obtained depending upon the analytical procedure used to treat the data; that is, the choice of reference baseline, the curve fitting procedure adopted and the method of comparing the reference baseline with the fitted curve. The estimates of the critical oxygen requirement of the central cornea are consistent with previous studies when compared using the same analytical procedure. Similar critical values were derived for the central and peripheral cornea for any given analytical procedure (e.g. 9.8% for the central cornea, and 12.3% for the peripheral cornea for zero mean change in corneal thickness). Our findings indicate that anatomical and physiological differences between the central and peripheral cornea do not have clinically significant effects on the minimum oxygen requirements at these respective sites. This result has implications with respect to lens design considerations for alleviating physiological stress of the cornea during contact lens wear.