In eight ophthalmic units, the investigator will include all inflammatory optic neuritis (ON) during acute phase and rank them in two groups: 1/ ON with autoantibodies anti-myelin-oligodendrocyte-glycoprotein (ON MOG+) 2/ ON MOG-. The investigators will measure incidence of MOG-Ab in our prospective population of inflammatory ON. Then the investigator will compare clinical and radiological presentation of ON MOG+ versus ON MOG-.

Optic neuritis (ON) have a broad clinical spectrum ranging from a single episode (clinically isolated ON) to demyelinating diseases such as multiple sclerosis (MS), Chronic Relapsing Inflammatory Optic Neuritis (CRION), acute demyelination encephalomyelitis (ADEM), neuromyelitis optica (NMO) and neuromyelitis optica spectrum disorder (NMOSD). Myelin oligodendrocyte glycoprotein (MOG) is a myelin antigen exclusively expressed on the surface of oligodendrocytes and myelin in the central nervous system (CNS). MOG-Ab are associated with demyelinating diseases with a good specificity. Using cell-based assays, MOG-Ab were rarely found in healthy control and other neurological inflammatory disease. They were mostly identified in subgroups of NMO/NMOSD seronegative to auto antibodies against Aquaporin 4 (anti-AQP4): 8-39%, but also in MS (0-28%) ADEM and idiopathic ON. ON MOG + have a specific clinical presentation compare with ON associated with multiple sclerosis (SEP): older patient, less female preponderance, more often bilateral, more often optic disc swelling, worse initial visual loss, much more often recurrent with severe sequelae. ON MOG+ are more similar to ON associated with NMOSD AQP4+ which have some particularities: similar age, clear female preponderance, less optic disc swelling, more severe initial visual loss and visual sequelae. No prospective study has measured incidence of

MOG-Ab in population of Inflammatory ON. And no prospective study has ever compared ON MOG+ with all others inflammatory ON. The purpose of our study is to measure incidence of MOG-Ab in population of acute inflammatory ON. All consenting adults with suspicion of ON followed in the 8 ophthalmic units who participate will be screened. They will have, as usual, clinical follow-up, blood test with MOG-Ab research, encephalic and optic nerves MRI, and steroid treatment if necessary. At the end of the acute phase, all patients diagnosed with inflammatory ON will be included and rank in 2 groups: 1/ ON with MOG-Ab (ON MOG+) 2/ ON without MOG-Ab (ON MOG-). Clinical data will be register at this inclusion visit. There will be no additional visit and no intervention. After measuring incidence of MOG-Ab, the investigator will compare clinical and radiological data of ON MOG+ and ON MOG-.

Inclusion Criteria:

• legally adult patient
• acute inflammatory optic neuritis
• consent

Exclusion Criteria:

• Patient under tutorship

Phe patients included will be mostly young adults between 18 and 40 years old, consultant in the ophthalmology department of the University Hospital of Nantes for an inflammatory optic neuropathy