Optic neuritis is inflammation of the optic nerve that can be caused by demyelination, infection, or other autoimmune processes. It is classified based on location of inflammation (retrobulbar, papillitis, neuroretinitis) and etiology. Common symptoms include sudden unilateral vision loss, eye pain on movement, and color vision changes. Examination may reveal reduced acuity, afferent pupillary defect, and optic disc swelling or atrophy. Brain MRI and lumbar puncture help diagnose underlying causes like multiple sclerosis. For demyelinating optic neuritis, high-dose intravenous steroids can hasten recovery of vision lost.