An inflammation, usually affecting just one eye, that damages the optic nerve, a bundle of nerve fibers that transmits visual information from your eye to your brain. Pain and temporary vision loss in one eye are common symptoms of optic neuritis.

Signs and symptoms of optic neuritis can be the first indication of multiple sclerosis, or they can occur later in the course of MS. Besides MS, optic neuritis can occur with other infections or immune diseases, such as lupus.
Most people who have a single episode of optic neuritis eventually recover their vision. Treatment with steroid medications may speed up vision recovery.
The exact cause of optic neuritis is unknown; it is believed to develop when the immune system mistakenly targets the myelin, which covers the optic nerve.

The Mayo Clinic. Internet. Accessed on January 14, 2019.