Pathologic studies of the blood--retinal barrier in the spontaneously diabetic BB rat.

The BB rat spontaneously develops a diabetic state that closely resembles human type I diabetes. The authors studied the pathologic changes of the retina and retinal pigment epithelium of four normal and nine diabetic BB rats using (1) light and electron microscopy with the horseradish peroxidase tracer technique, and (2) trypsin digest preparations of the retinal vessels. They observed a retinal pigment epitheliopathy characterized by (1) derangement of the plasmalemma infoldings; (2) patchy organelle degeneration leading to focal necrosis; (3) increased permeability to horseradish peroxidase; and (4) repair of the pigment epithelium. Focal thickening of the retinal vascular basement membrane was seen occasionally, but the trypsin digest preparations were unremarkable. These studies suggest that diabetic retinal pigment epitheliopathy may be one of the early changes of diabetic retinopathy and may provide a pathogenetic mechanism for early disruption of the blood-retinal barrier.