Optic neuritis is a condition that presents inflammatory demyelination of the optic nerve, resulting in painful loss of vision in one eye. This visual loss gradually develops over several days, with pain occurring around the orbit (socket) with eye movement. Visual function begins to improve over several weeks, and usually returns to normal by three months. Color vision is the last sensory faculty to return to those affected by optic neuritis.
In 20-30 percent of patients, optic neuritis is the first symptom of MS. MRI scanning helps to differentiate those patients who are more likely to develop MS. Other possible causes of optic neuritis include infections such as syphilis, Lyme disease, sarcoidosis or lupus.