Nonspecific orbital inflammation is an idiopathic chronic tumor-like inflammation process that usually affects the orbital tissues of both eyes. Isolated optic nerve involvement by an idiopathic inflammatory process is a rare finding. Here, we report a patient with unilateral sudden onset severe orbital pain and headache with visual loss to no light perception that could only be attributed to perineuritis. Radiological findings enabled making the correct diagnosis. Various relevant diagnoses are also discussed.