Disorders of the Optic Nerve in Horses

Optic nerve hypoplasia is a failure of the optic nerve to develop fully. It is a congenital disorder in horses. The condition may occur in only one eye or both, and it can occur with or without other eye abnormalities. If the optic nerves of both eyes fail to develop, the foal will be blind. Involvement of only one of the optic nerves often goes undetected or may be discovered later in life if the other eye acquires a blinding disease.

Optic nerve degeneration or atrophy may occur as a result of equine recurrent uveitis, glaucoma, trauma, advanced degeneration of the retina, prolonged low blood pressure within the eye, or inflammation. The optic disk appears flattened and smaller than normal; it is often discolored, with very noticeable reduction in the optic nerve and blood vessels of the retina. Affected animals are blind. There is no treatment.

Optic neuritis is inflammation of the optic nerve. When it affects both eyes, the animal suddenly becomes blind, with dilated, unmoving pupils. Your veterinarian will diagnose the condition by examining your horse's eyes with an ophthalmoscope, performing visual reflex tests and completing a neurologic examination. In addition, a blood test, x-rays, and other tests may also be necessary to identify the cause. Optic neuritis can occur due to viral, fungal, protozoal, or parasitic infections; poisons; trauma; and other causes. Treatment is directed at managing the underlying disease and usually includes the use of medications to decrease inflammation and damage.

Proliferative optic neuropathy occurs primarily in older horses. It usually involves only one eye and has a minimal effect on vision. Signs include a yellow-white mass that protrudes from the optic disk into the vitreous (the clear “jelly” that fills the eye). There is no treatment.

Also see professional content regarding disorders of the optic nerve in animals.