Optic Nerve Hypoplasia
The optic nerves––located at the back of the eyes where they establish a direct connection to the brain––are responsible for vision. Optic nerve hypoplasia is a condition that uncommonly affects the optic nerves of cats and dogs, leading to a variable degree of vision reduction (or even blindness) in one or both eyes.
In some cases, the eyes of affected animals are otherwise normal. In other instances, the eyes are malformed in a variety of ways. In all cases, the optic nerves are smaller than they should be. Beyond an understanding of its genetic origins, exactly how this disease occurs is not well understood.
In kittens, optic nerve hypoplasia may occur as a result of panleukopenia (feline distemper) infection.
Symptoms and Identification
Diagnosis usually occurs incidentally in the course of normal ophthalmic evaluation or because vision impairment is suspected. The animal may exhibit previously unrecognized evidence of blindness in one or both eyes (by failing to respond normally to light, unilaterally), in which case confirmation of the diagnosis occurs through fundoscopic examination (visualizing the back of the eye with a lens) of a smaller-than-normal optic disc.
Severely affected (completely blind) animals are typically diagnosed immediately after birth.
Optic nerve hypoplasia appears to be heritable in Poodles. Collies may also be predisposed.
No treatment is available for this condition.
The cost of diagnosis is relatively minor, though opthamologist consultation is strongly recommended and may increase the cost of diagnosis into the low hundreds of dollars.
Affected and carrier individuals should be removed from the breeding pool.
Barr, Bradd C.; Murphy, Christopher J.; Ghazikhanian, G. Yan and Bellhorn, Roy W. Cataracts and optic nerve hypoplasia in turkey poults. Avian Diseases 1988;32:469-477.
Kern, Thomas J. and Riis, Ronald C. Optic nerve hypoplasia in three miniature poodles. Journal of the American Veterinary Medical Association 1981 (1 January);178 (1):49-54.
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