MOG and neuritis: Atypical ON has a somewhat different clinical picture from typical ON, and encompasses neuromyelitis optica spectrum disease (NMOSD), myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD), idiopathic recurrent neuroretinitis (NR), chronic relapsing inflammatory ON (CRION), ON within systemic autoimmune diseases, paraneoplastic and neuritis during or after infectious diseases or vaccination.