Optic neuritis is inflammation of the optic nerve, the nerve that carries the visual signal from the eye to the brain.The conditionmay cause sudden, reduced vision in the affected eye(s). While the cause of optic neuritis is unknown, it has been associated with autoimmune diseases, infections, multiple sclerosis, drug toxicity and deficiency of vitamin B-12. Vision often returns to normal within 2-3 weeks without treatment. In some cases, corticosteroids are given to speed recovery. If known, the underlying cause should be treated. The disease is MONDO_0005885 (optic neuritis).