Ultrastructural aspects of human and canine diabetic retinopathy.

Diabetic retinopathy has been examined in dogs made diabetic by bovine growth hormone or alloxan, and in humans. The thin-walled microaneurysm is a simple expansion of the circumference of the capillary with basement membrane thickening. The thick-walled microaneurysm represents the deposition of considerable debris between layers of thickened basement membrane, as well as compression phenomenon of the adjacent retinal tissues and a secondary reactive gliosis. These thick-walled microaneurysms are markedly permeable to all elements of the blood. No specific morphological change has been found to explain the focal nature of the initial dilatation of capillaries to form microaneurysms, or the unusual permeability of these areas. Death of pericytes may play a role in development of diabetic retinopathy. The reason for the death of these cells is unknown but may be related to the metabolic derangements of diabetes itself.