Hereditary retinal degeneration in the Abyssinian cat: correlation of ophthalmoscopic and electroretinographic findings.

Ophthalmoscopic and electroretinographic (ERG) findings were correlated in a group of Abyssinian cats affected by a slowly progressive and hereditary retinal degenerative disease. According to ophthalmoscopic findings the disease was divided into stages. At stage 1 and 2 retinal changes were minor; showing a gray discoloration most often in the peripheral and midperipheral tapetal fundus. At stage 3 discoloration was generalized and there was marked vascular attenuation. A generalized retinal atrophy was found at stage 4. ERG recordings showed an abnormally depressed stimulus response curve for the b-wave at stage 1 of disease when 30-Hz cone flicker responses were indistinguishable from normal. With progression of disease there was a successive decrease of a- and b-wave amplitudes before there was a significant reduction also of the c-wave amplitude (first seen at stage 3). The ERG was nonrecordable at stage 4. These findings suggest that the photoreceptors are affected primarily by the disease, before there is a functional involvement also of the pigment epithelium. The rod system seems to be affected early in the disease as compared with the cone system. A staging of the disease by ophthalmoscopy correlated more to the function of the rods than to that of the cones.