Bilateral aplasia of the optic nerve in a cat.

Congenital absence of the optic nerve in man is a very rare anomaly (Duke-Elder, I963, I964). In true cases the optic disc, optic nerve fibres, and central retinal blood vessels are absent on ophthalmoscopic examination. Hypoplasia of the optic nerve, which is also rare, occurs when some or all of the nerve fibres fail to develop and reach the disc. The condition may be unilateral or bilateral, and may be found in grossly malformed eyes or in those that are otherwise normal. Retinal vessels are present, however, although they may be greatly attenuated. The absence of retinal vessels necessarily involves a complete lack of vision. Hypoplasia of the optic nerve has been described in the horse (Gelatt, Leipold, and Coffman, i969), cattle (Leipold and Huston, i968), and dogs (Saunders, 1952; Gelatt and Leipold, 1971). Aplasia of the optic nerve has been recorded in the cat ((Abderhalden, 1903; Zeeman and Tumbelaka, I9I6; Szymanski, I926; Veenendaal, 1936) and the mouse (Bein, 1947). This report records the ophthalmoscopic and pathological features of bilateral aplasia of the optic nerve in a cat.