Merck Manual

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Professional Version

Optic Nerve


Kirk N. Gelatt

, VMD, DACVO, Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida

Last review/revision Jun 2014 | Modified Oct 2022
Topic Resources

Optic nerve diseases are often difficult to detect and diagnose. Of the optic nerve diseases, inflammation of the optic nerve (optic neuritis) is most frequent.

Optic nerve hypoplasia may be inherited in Miniature Poodles; in kittens and calves, it may result from in utero infections with panleukopenia and bovine viral diarrhea, respectively. In calves, the cause may be maternal avitaminosis A. The condition may be unilateral or bilateral, and it can occur with or without other ocular anomalies. Bilateral involvement is manifest as blindness in the neonate; unilateral involvement is often an incidental finding later in life or becomes manifest if the other eye acquires a blinding disease.

Bilateral optic neuritis produces acute blindness and dilated and fixed pupils. On ophthalmoscopy, the optic nerve head or optic disc is raised, edematous with blurred margins and peripapillary hemorrhages, venous congestion, and often inflammatory cells in the adjacent retina and vitreous. Causes of optic neuritis may vary by species affected and include viral, mycotic, protozoan and parasitic infections, trauma, reticulosis, toxins, and other causes. Complete physical and medical evaluations are usually necessary to establish the possible diagnoses. Specific therapies are directed toward the cause, and systemic corticosteroids are important to reduce inflammation of and damage to the optic nerve.

Papilledema is rare in animals and often associated with orbital masses in most domestic species. Increased intracranial pressure does not usually result in papilledema in animals, except in calves with avitaminosis A. The optic disk appears raised above the surface of the adjacent retina, and venous congestion is present. Vision and the light pupillary reflexes are not usually affected unless optic atrophy develops.

Optic atrophy may develop after glaucoma, trauma, advanced retinal degeneration, prolonged ocular hypotension, or inflammation. The optic disk appears depressed and smaller than normal; it is often pigmented, with marked reduction in the optic nerve and retinal vasculature. Both direct pupillary reflex and vision are absent. There is no treatment.

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