Optic perineuritis can be a manifestation of infectious and systemic inflammatory disorders, but in most cases is considered idiopathic. Diagnosis is established by magnetic resonance imaging (MRI) with the demonstration of optic nerve sheath enhancement with sparing of the optic nerve itself. Myelin oligodendrocyte glycoprotein (MOG)-IgG-positive optic neuritis has been reported in association with optic nerve sheath enhancement. The authors present two MOG-IgG patients with clinical, radiological and therapeutic response consistent with optic perineuritis. They suggest that MOG-IgG may therefore account for other cases of previously described idiopathic optic perineuritis. In summary, patients presenting with vision loss with optic nerve sheath enhancement on MRI should prompt testing for MOG-IgG. A confirmed diagnosis can assist in decision-making regarding treatment and prognosis.