Optic neuritis is inflammation of the optic nerve, which connects the eye to the brain. Optic neuritis causes vision loss, usually in one eye only. Many people find that it hurts to move the eye as well. Optic neuritis is a very common symptom of multiple sclerosis (MS), but having optic neuritis does not mean you have MS. In fact, 50% of people with optic neuritis will never get MS. Your doctor will probably ask you to have an MRI to help predict your risk of getting MS.
Optic neuritis improves on its own without any treatment. If you have a more severe case, high dose steroids can help the vision recover faster. Steroids can be taken by mouth or by IV and work just as well either way.