Distribution of underlying ON etiologies was as follows: 78 (49%) patients had a single isolated ON, 41 (26%) patients were diagnosed with multiple sclerosis, 25 (16%) patients with myelin oligodendrocyte glycoprotein antibody‐associated disease, and 15 (9%) with neuromyelitis optica spectrum disorder. The gene discussed is MOG; the disease is neuromyelitis optica.