Ischemic optic neuropathy.

Ischemic optic neuropathies (IONs) are the most frequent acute optic neuropathy in patients older than 50 years. They are classified according to the location of the ischemic damage into anterior ION and posterior ION. Ischemic optic neuropathies may also be categorized based on the presence or absence of temporal arteritis as an underlying etiology. Anterior ION presents with sudden, painless visual loss developing over hours to days. Examination findings usually include decreased visual acuity, a visual field defect, color vision loss, a relative afferent pupillary defect, and a swollen optic nerve head. Posterior ION occurs in arteritic, nonarteritic, and surgical settings. It is characterized by acute vision loss without initial disc edema but with subsequent optic disc atrophy.