Fine structure of the retinal pigment epithelium, Bruch's membrane and choriocapillaris in the horse

The fine structure of the retinal pigment epithelium (RPE), Bruch's membran e and choriocapillaris was investigated by light and transmission electron microscopy in both the tapetal and non-tapetal fundus of the horse eye. In all locations, the RPE consisted of a single layer of low cuboidal cells. T he epithelial cells were joined laterally by apically located tight junctio ns. These cells displayed numerous basal infoldings and abundant thin apica l processes which enclosed the rod outer segments. The the epithelial cell nuclei were large and located basally. Within the epithelial cells, smooth endoplasmic reticulum was very abundant, while rough endoplasmic reticulum was scarce, polysomes and mitochondria, which often display a ring-shaped s tructure, were abundant. Melanosomes were abundant in the non-tapetal area but absent ill the tapetal area. Bruch's membrane was pentalaminate through out the retina. The endothelium of the choriocapillaris was heavily fenestr ated.