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.
The most frequent optic nerve disease is optic neuritis, which is inflammation of the optic nerve. When it affects both eyes, signs include dilated pupils that do not respond to light and also sudden blindness that is not due to another eye disease. Your veterinarian will diagnose the condition by examining your cat'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 inflammation of the brain; viral, fungal, protozoan 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. If treatment is successful, pupils will return to normal size and respond to light within several days, followed by a return of vision a few days later.
Failure of the optic nerve to develop fully (optic nerve hypoplasia) in kittens may result from infections with panleukopenia (feline distemper, a viral infection) while in the mother’s womb. 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 newborn 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 degeneration or atrophy may occur after 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 colored, with very noticeable reduction in the optic nerve and blood vessels of the retina. The pupil of the eye will not react to light, and vision is absent. There is no treatment.