EFFECTS OF CATARACT-SURGERY ON CORNEAL FUNCTION

Abstract

The aphakic eye may develop less corneal edema than the phakic eye during hydrogel contact lens wear. Measurements were made of several ocular characteristics that might account for this difference in 9 unilateral aphakic [human] subjects. The measurements showed that compared with the phakic eye, the aphakic eye averaged a 15% lower epithelial O2 uptake rate, 18% fewer endothelial cells, 85% loss of corneal sensitivity, and 8% thinner corneal epithelium. Both eyes of each subject were exposed to a reduced O2 environment for 2 h in separate experiments: by wearing a thick hydrogel contact lens and closing the eyes, and by exposing the eye to 100% N2 gas. In the gel lens-closed eye experiment the aphakic cornea swelled an average of 7.5%, compared with 11.0% for the phakic cornea. For the N2 gas experiment the results were 4.3 and 6.2%, respectively. Of the edema, 85% was in the stromal layer. The lower swelling response for the aphakic eye was significant (P < 0.01) in both experiments. Corneal swelling after hypoxia is considered to be caused by an increase in corneal osmolarity resulting from an increase in the rate of production of lactic acid. The reduced corneal swelling in the aphakic eye, when compared with the phakic eye, could be the result of either a reduction in the overall metabolic activity of the epithelium, as indicated by the lower epithelial O2 uptake rate and the thinner corneal epithelium in the aphakic eye, or an increased efflux of lactic acid from the cornea resulting from an increased endothelial permeability to lactate.