Corneal nerve alterations in diabetes mellitus.

The morphologic status of corneal innervation was studied in rats with streptozocin-induced diabetes. Animals were killed at 1, 4, 16, and 36 weeks. Corneal innervation was studied by light and electron microscopy using nonspecific cholinesterase reaction, gold chloride impregnation, and plastic-embedded sections. Increased irregularity in the periodicity of nerve fiber beading was observed in diabetic corneas with gold impregnation. Ultrastructural evidence of irregularities in the basal lamina of Schwann cells was demonstrated in 16- and 36-week-old diabetic animals, along with occasional axonal degeneration. These alterations constitute a constellation of early pathologic manifestations in the innervation of diabetic cornea. To our knowledge, this study represents the first demonstration of neural changes in diabetic corneas as well as nerve fiber changes in an avascular tissue in diabetes.