Abnormal light scattering detected by confocal biomicroscopy at the corneal epithelial basement membrane of subjects with Type II diabetes

Aims/hypothesis. Abnormalities of the basement membrane are thought to contribute to the complications of diabetes. The suitability of the cornea for detecting such abnormalities was assessed by determining its light-scattering index, a quantitative measure of tissue reflectivity in the basement membrane zone, with a confocal biomicroscope. Methods. The light-scattering index was measured in 65 subjects with Type II (non-insulin-dependent) diabetes mellitus and 18 control subjects and was evaluated for its possible relation to the stage of diabetic retinopathy. Diabetic retinopathy was staged by ophthalmoscopic examination as non-diabetic (NDR), simple (SDR), preproliferative (PPDR), or proliferative (PDR). Results. Examination of the cornea layer-by-layer with a confocal biomicroscope did not show any marked differences in morphology between diabetic and control subjects. The LSI (mean +/- SD) was 0.81 +/- 0.13, 0.87 +/- 0.09, 0.90 +/- 0.09, 0.90 +/- 0.13, and 1.02 +/- 0.25 in control subjects and in diabetic subjects with NDR, SDR, PPDR, or PDR, respectively; the light-scattering index of diabetic subjects with PDR was significantly greater than that of the control subjects (p = 0.001). An LSI greater than 1.0 was detected in 5.6, 6.3, 15.0, 15.4, and 50.0 % of control subjects and of patients with NDR, SDR, PPDR, or PDR, respectively; the percentage of subjects with an LSI greater than 1.0 was significantly increased in diabetic patients with PDR than for control subjects. Conclusion/interpretation. These results suggest that the LSI increases with the stage of diabetic retinopathy, and that measurement of corneal light scattering could provide an index of basement membrane abnormality in people with diabetes.