CORNEAL HYDRATION CONTROL IN DIABETES-MELLITUS

Purpose. To assess the effects of diabetes mellitus on corneal structu re and function. Methods. The authors measured endothelial permeabilit y to fluorescein and corneal deswelling for 7.5 hours after 2 hours of hypoxic contact lens wear in 20 patients with diabetes who had nonpro liferative retinopathy and 21 age-matched control subjects. Central co rneal endothelial photographs were also taken. Corneal deswelling rate s, expressed as percent recovery per hour (PRPH), and open eye steady state (OESS) thickness were estimated by nonlinear regression techniqu es. Results. The OESS thickness was greater in patients with diabetes than in controls (562 +/- 35 mu m versus 539 +/- 24 mu m, P = 0.02). D uring hypoxia, the diabetic corneas swelled less (7.7% +/- 1.8% versus 9.9% +/- 1.6%, P < 0.001) and had less endothelial permeability (3.55 +/- 0.83 X 10(-4) cm/min versus 4.14 +/- 0.68 X 10(-4) cm/min, P = 0. 02) than the controls. During normoxia after contact lens removal, how ever, diabetic and control corneas had similar deswelling rates and pe rmeabilities. Corneal autofluorescence was increased in the patients w ith diabetes (8.1 +/- 3.1 versus 6.0 +/- 1.9 ng/ml fluorescein equival ents, P=.005). The endothelial cells of the two groups were morphologi cally similar. Within the group with diabetes, however, those with mod erate nonproliferative retinopathy had larger coefficients of variatio n of cell area and smaller percentages of hexagonal cells than those w ith mild nonproliferative retinopathy. Conclusions. Although the diabe tic corneas were thicker and more autofluorescent than control corneas , during hypoxia they swelled less and had decreased endothelial perme ability. During normoxia, however, no difference was found in endothel ial permeability or deswelling rate. The effects of diabetes on endoth elial cell morphologic features appear to be related to the severity o f the diabetes.