Production of hypoxia-induced corneal edema in aged eyes

Corneal thickness assessment is a common clinical procedure applied in corneal and contact lens care. This study aims to investigate the effect of age on hypoxia-induced corneal swelling.

Eighteen male subjects were equally divided into the younger [(23.7 +/- 0.8) years old] and older [(74.4 +/- 2.5) years old] groups. Each subject wore a thick soft contact lens (uniform thickness of 0.3 mm) on the left cornea. With the contact lens in place, the baseline central corneal thickness was measured using a specially designed photo-pachometer. The lens was then patched behind the closed eyelids, producing an extremely hypoxic stress to the cornea. The change in central corneal thickness was monitored every 20 minutes with momentary disruptions to the hypoxic stress over the next 2 hours. The increase in thickness was taken as an index of corneal edema. The rate of change in corneal thickness, as derived from a non-linear mathematical model, was compared between groups.

The corneal thickness of both age groups increased significantly with time (P < 0.0001). The mean corneal swelling constant for the older subjects was 16.5 x 10(-3) (S.E.M. = 2.65 x 10(-3)) and the value for the younger subjects was 46.5 x 10(-3) (S.E.M. = 3.25 x 10(-3)). The difference was statistically significant (P < 0.0001).

Aging cornea has a slower hypoxia-induced edema response compared with the younger group. Whether it is caused by a decreased corneal lactate production or an increased resistance to physical expansion deserves further investigation.