Initially discovered in patients with multiple sclerosis-associated optic neuritis [9,10], MME was later found in various causes of OA [11]: anti-aquaporin-4 antibody-positive optic neuritis [12], relapsing isolated optic neuritis [13], Leber hereditary optic neuropathy and autosomal dominant optic atrophy [14], acute anterior ischemic optic neuropathy, compressive optic neuropathy, toxic and nutritional optic neuropathy, traumatic optic neuropathy, and glaucoma [15]. This evidence concerns the gene AQP4 and optic neuritis.