Ocular anomalies of incomplete albino Hereford cattle

Abstract

Eye anomalies of 15 Hereford albino cattle were observed clinically and compared with those detected histologically. Iris colour ranged from blue and white to a combination of blue, white and brown or grey. The irides were thinner than normal and permitted trans-illumination. The tapetal fundi were usually a red-yellow, and the nontapetal fundi were incompletely pigmented. Optic nerve head and nontapetal fundi colobomata varied markedly in size. The typical colobomata of the optic nerve head and nontapetal fundi were divided into small and large types. In the small colobomata, the retina was thinned primarily by loss of photoreceptors, outer nuclear layer, and to a lesser extent the inner nuclear layer. There was no choroid in the coloboma, and the sclera was normal. In the large typical colobomata, changes of the optic nerve head, retina, choroid, and sclera were pronounced. The ventral optic nerve head was marked by irregular depressions of varying depths. The retinal pigment epithelial layer was incomplete and replaced with occasional irregular groups of cells. The choroid was absent in the colobomata and the sclera thinner than normal.