Optic nerve neuritis is one of the most important differential diagnoses of visual loss in young and middle aged adults. The prognosis in terms of functional outcome is generally good. The diagnosis of optic neuritis is clinical. Steroids can reduce the recovery time but do not affect the long-term functional outcome. Magnetic resonance imaging (MRI) is the most important investigation for assessing an associated risk of multiple sclerosis. Optical coherence tomography (OCT) contributes additional details on the course and functional outcome of optic neuritis. In the future OCT may additionally contribute to the relationship between optic neuritis and possible associated multiple sclerosis.