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 see Eye Disorders of Horses: Equine Recurrent Uveitis (Periodic Ophthalmia, Moon Blindness), glaucoma, trauma, advanced degeneration of the retina, prolonged low pressure within the eye, or inflammation. The optic disk appears flattened and smaller than normal; it is often pale or white, with very noticeable reduction in the optic nerve and blood vessels of the retina. Both the direct reflex of the pupil and vision are absent. There is no treatment.
Proliferative Optic Neuropathy
This condition 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.
Last full review/revision July 2011 by Kirk N. Gelatt, VMD; David G. Baker, DVM, MS, PhD, DACLAM; Steven R. Hollingsworth, DVM, DACVO