Progressive ultrastructural damage and thickening of the basement membrane of the retinal pigment epithelium in spontaneously diabetic BB rats.

Ultrastructural examination of the neural retina and retinal pigment epithelium was performedin spontaneously diabetic BB rats and non-diabetic littermate controls at various time points dunring the course of diabetes. Four types of progressive changes occur in diabetic rats: (1) There is a progressive thickening of the basal laminae of the retinal pigment epithelium and the retinal capillaries. (2) In addition to this thickening, there is a progressive, often focal, thickening of the rest of Bruch's membrane, and by 111/2 months it contains numerous randomly oriented collagen fibrils. (3) There are progressive ultrastructural changes in retinal pigment epithelial cells consisting of marked dilation of the basal infoldings, the formation of large vacuoles and cell swelling. (4) Rare degenerative changes were noted in retinal capillary pericytes. Since non-diabetic littermates do not show comparable changes, it is likely that they are diabetes-related, suggesting that progressive damage to the retinal pigment epithelium may occur during the course of diabetes.