The optic nerve carries the electrical impulses from the eye to the area in the back of the brain where vision is sensed and interpreted. Injury to the optic nerve usually leads to partial or complete loss of sight.
Optic Nerve Hypoplasia
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 Atrophy
Optic nerve degeneration or atrophy may occur as a result of equine recurrent uveitis Equine Recurrent Uveitis (Periodic Ophthalmia, Moon Blindness) The uvea (or the uveal tract) is the colored inside lining of the eye consisting of the iris, the ciliary body, and the choroid. The iris is the colored ring around the black pupil. The ciliary... read more , glaucoma Glaucoma in Horses The glaucomas represent a group of diseases characterized by increased pressure within the eye. The high pressure eventually destroys the retina and optic disk (the spot where the optic nerve... read more , 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
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.