IgG4-related orbital disease presenting as optic neuropathy: A rare presentation and review of literature

A 74-year-old male presented with a sudden drop of vision in the left eye for 5 days. He had a relative afferent pupillary defect and visual acuity of counting finger at 1 m in the left eye. Fundus showed a hyperaemic disc in the left eye. Ocular movements were full. He had uncontrolled diabetes mellitus. A possibility of anterior ischemic optic neuropathy was considered. The patient was lost for follow-up and came back 2 months later with visual acuity of perception of light in the left eye with features suggestive of orbital apex syndrome. Histopathology was confirmatory of immunoglobulin G4 (IgG4) disease. IgG4 disease presenting as optic neuropathy can be an early manifestation of orbital involvement.