Optic neuritis is regarded as an immune-mediated inflammatory disorder affecting any portion of the optic nerve. It most commonly begins with pain in the ipsilateral orbit followed by rapidly progressive loss of visual function over several days. The vision begins to improve within 2 to 4 weeks, and recovery is fairly rapid over another 2 to 3 weeks followed by slow further improvement up to 1 year. The pain typically resolves ahead of visual dysfunction — usually within the first 2 weeks.