Corneal autofluorescence in diabetic and normal eyes

Corneal autofluorescence has been lately studied as a predictor of retinopathy severity in diabetic patients. We measured corneal autofluorescence in 138 eyes of 69 diabetic patients and 64 eyes of 32 healthy controls. Diabetic patients were subdivided by the severity of retinopathy according to the Modified Airlie House Classification (stage 1: no or minimal retinopathy; stage 2: minimal background retinopathy; stage 3: background retinopathy; stage 4: (pre-) proliferative retinopathy. The fluorescence peak value and the area underlying the corneal autofluorescence curve were measured with a scanning fluorophotometer (Fluorotron Master, Coherent Radiation Palo Alto CA) Healthy controls' values of corneal autofluorescence (peak value: mean 11.03 +/- 3.77 ng. equivalent fluorescein/ml; area: mean 163.85 +/- 61.40 scan-point x ng. equivalent fluorescein/ml) resulted similar (peak value: p = 0.83; area: p = 0.61) to those of diabetic patients without retinopathy (peak value: mean 11.2 +/- 3.4 ng.eq/ml; area: 170.07 +/- 57.23 scan-pnt.ng.eq/ml). A statistically significant difference was found between diabetic patients without retinopathy and patients with stage 2, 3, 4 retinopathy. No statistically significant difference was found both for the peak value (p = 0.50) and for the area (p = 0.61) between stage 3 and stage 4 retinopathy. The sensitivity and specificity of corneal autofluorescence as a screening test for diabetic retinopathy were 82% and 62% for the peak value, 87% and 60% for the area; the positive predictive value for the presence of diabetic retinopathy was 65% for the peak and 63% for the area.