Optic neuritis is inflammation of the optic nerve. It may cause sudden, reduced vision in the affected eye. The exact cause of optic neuritis is unknown. The optic nerve carries visual information from your eye to the brain. Sudden inflammation of this nerve can cause the optic nerve to swell. This can result in injury to the nerve fibers and some or permanent loss of vision. Conditions that have been linked with optic neuritis include: autoimmune diseases, including lupus, sarcoidosis, Behcet’s disease, and more. Symptoms include loss of vision in one eye over an hour or a few hours, changes in the way the pupil reacts to bright light, loss of color vision, and pain when you move the eye. Vision often returns to normal within 2 to 3 weeks with no treatment. People who have optic neuritis without a disease such as multiple sclerosis have a good chance of recovery.