Retinal degeneration in the WKY rat.

An outer retinal degeneration occurs in middle aged Wistar-Kyoto (WKY) rats, the normotensive counterpart to the spontaneous hypertensive rat strain (SHR). The degeneration, like that of other spontaneous and experimentally-induced outer layer retinopathies of rats, is characterized by a progressive loss of photoreceptor and outer nuclear layers which, in turn, leads to contact between the deep capillary bed of the retina and the retinal pigment epithelial (RPE) cells. RPE proliferation and/or migration causes a number of capillaries to become enmeshed within RPE cells, and some of those capillaries undergo morphologic and physiologic alterations such that they resemble choroidal capillaries. There is variable loss of the choriocapillaris associated with this retinopathy, but since this is also seen to some degree in normal eyes, it is not known if this is an integral part of the pathologic process.