Retinal vessel abnormalities of phototoxic retinopathy in rats

Phototoxic retinopathy in rats is characterized by a progressive loss of the outer retinal layers. During the neural degenerative phases, a sequence of vascular change occurs. Whole mounts of ink-injected retinal vessels and flat mounts of trypsin-digested retinal vessels show areas of capillary nonperfusion and acellularity and enlargement of retinal capillaries in the deep bed. When the photoreceptor and outer nuclear layers have disappeared, portions of the remaining deep capillary bed become surrounded by cells of the retinal pigment epithelium (RPE). Thin sections show fenestrae in some vessel walls within the retinal pigment epithelial layer. Since serial sections show continuity between those fenestrated vessels and the deep retinal vessels and no evidence of vessels breeching Bruch's membrane, this morphologic phenomenon is considered to be an in situ alteration of retinal vessels. We conclude that a factor(s) within the retinal pigment epithelial layer determines the morphology of vessels within that environment.