of the posterior ciliary arteries that supply the anterior portion of the optic nerve—produces sudden visual loss, usually with an altitudinal field defect, and optic disk swelling
In older patients, it may be caused by giant cell arteritis (arteritic anterior ischemic optic neuropathy)
The predominant factor predisposing to nonarteritic ante- rior ischemic optic neuropathy, which subsequently affects the fellow eye in around 15% of cases, is a congenitally crowded optic disk
Other predisposing factors are sys- temic hypertension, diabetes mellitus, hyperlipidemia, systemic vasculitis, inherited or acquired thrombophilia, interferon-alpha therapy, obstructive sleep apnea, and phosphodiesterase type 5 inhibitors
Ischemic optic neuropathy, usually involving the retro- bulbar optic nerve and thus not causing any optic disk swelling (posterior ischemic optic neuropathy), may occur with severe blood loss; nonocular surgery, particu- larly prolonged lumbar spine surgery in the prone position; severe burns; or in association with dialysis
In all such situations, there may be several contributory factors

Treatment

Arteritic anterior ischemic optic neuropathy necessitates emergency high-dose systemic corticosteroid treatment to prevent visual loss in the other eye
(See Central & Branch Retinal Artery Occlusions, above, and Polymyalgia Rheu- matica & Giant Cell Arteritis, Chapter 20
) It is uncertain whether systemic or intravitreal corticosteroid therapy influences the outcome in nonarteritic anterior ischemic optic neuropathy or whether oral low-dose (~81 mg daily) aspirin reduces the risk of fellow eye involvement
In isch- emic optic neuropathy after nonocular surgery, treatment of marked anemia by blood transfusion may be beneficial

When to Refer

Patients with ischemic optic neuropathy should be referred urgently to an ophthalmologist

When to Admit Patients with ischemic optic neuropathy due to giant cell arteritis or other vasculitis may require emergency admis- sion for high-dose corticosteroid therapy and close moni- toring to ensure that treatment is adequate