RETINAL-PIGMENT EPITHELIAL DYSTROPHY IN BRIARD DOGS

The eyes of normal Briard dogs, Briards affected with inherited retina l pigment epithelial dystrophy (RPED) and a range of normal crossbred and beagle dogs were examined and the histopathology of RPED in the Br iard was compared with the histopathological features of ageing in the normal canine retina. RPED was characterised by the accumulation of a uto-fluorescent lipofuscin-like inclusions in the retinal pigment epit helium (RPE), which initially involved only non-pigmented RPE cells ov erlying the tapetum but subsequently spread to all pigmented RPE cells . Secondary neuro-retinal degeneration was characterised by a gradual loss of the outer nuclear layer and the subsequent atrophy and degener ation of the inner retina. The loss of primary photoreceptors in the p eripheral retina was accompanied by the migration of photoreceptor nuc lei and appeared to resemble severe changes due to ageing. Intra-vitre al radiolabelled leucine was used to examine the rate of turnover of t he outer segments of the rods in some Briards, but no significant vari ations were found. The activity of acid phosphatase in RPE was assayed in vitro and showed comparable regional variations in Briard and cros sbred dogs. The results suggest that RPED in the Briard is unlikely to be due either to an increased rate of turnover of rod outer segments (and thus an increased phagocytic load) or to a primary insufficiency of lysosomal enzyme.