Corneal structure and sensitivity in type 1 diabetes mellitus

PURPOSE. Corneal wound healing is impaired in diabetic cornea. The purpose of this study was to examine patients with type 1 diabetes mellitus for cha nges in corneal morphology and to correlate corneal sensitivity, subbasal n erve morphology, and degree of polyneuropathy with each other. METHODS. Forty-four eyes of 23 patients with diabetes and nine control eyes were included. Corneal sensitivity was tested with a Cochet-Bonnet esthesi ometer (Luneau, Paris, France), and corneal morphology and epithelial and c orneal thickness were determined by in vivo confocal microscopy. The densit y of subbasal nerves was evaluated by calculating the number of long subbas al nerve fiber bundles per confocal microscopic field. The degree of polyne uropathy was evaluated using the clinical part of the Michigan Neuropathy S creening instrument (MNSI) classification, and retinopathy was evaluated us ing fundus photographs. RESULTS. A reduction of long nerve fiber bundles per image was noted to hav e occurred already in patients with mild to moderate neuropathy, but cornea l mechanical sensitivity was reduced only in patients with severe neuropath y. Compared with control subjects the corneal thickness was increased in pa tients with diabetes without neuropathy. The epithelium of patients with di abetes with severe neuropathy was significantly thinner than that of patien ts with diabetes without neuropathy. CONCLUSIONS. Confocal microscopy appears to allow early detection of beginn ing neuropathy, because decreases in nerve fiber bundle counts precede impa irment of corneal sensitivity. Apparently, the cornea becomes thicker in a relatively early stage of diabetes but does not further change with the deg ree of neuropathy. A. reduction in neurotrophic stimuli in severe neuropath y may induce a thin epithelium that may lead to recurrent erosions.