Ischemic disorders are termed "arteritic" when they occur secondary to inflammations of blood vessels, chiefly giant cell arteritis (temporal arteritis). They are termed nonarteritic when they are secondary to occlusive disease or other noninflammatory disorders of blood vessels.
Optic neuropathy is divided into anterior, which causes a pale edema of the optic disk, and posterior, in which the optic disk is not swollen and the abnormality occurs between the globe and the optic chiasm.
Anterior ischemic optic neuropathy involves interruption of the blood flow in the short posterior ciliary arteries that supply the optic disk. This results in a severe loss of vision, altitudinal visual field defects, and a pale, swollen optic disk, with peripapillary hemorrhages.
Ischemic anterior optic neuropathy usually causes a loss of vision that may be sudden or occur over several days. Patients are generally older than those with optic neuritis. There is often loss of the inferior visual field. An afferent pupillary defect is present. The optic disk is swollen and may resemble that seen in papilledema or the swelling may be minimal.
Anterior optic neuropathy is divided into arteritic and idiopathic types. The arteritic type is less common (25 percent) and associated with inflammation of blood vessels. The idiopathic type involves mainly vascular occlusive disease or disorders that reduce the circulation of blood in the short posterior ciliary arteries that supply the optical disk.
Posterior ischemic optic neuropathy is an uncommon type of neuropathy and diagnosis depends largely upon exclusion of other causes, chiefly stroke and brain tumor. There are altitudinal visual field defects sometimes combined with decreased visual acuity. Decreased blood flow in the minute pial vessels supplying the nerve, connective tissue disorders, diabetes mellitus, trauma, and radiotherapy to the orbit have all been described as causes.
Impairment of visual acuity in ischemic optic neuropathy may vary from slight - with a corresponding decrease in color vision - to no light perception.
Age is the primary risk factor for anterior ischemic optic neuropathy.
For posterior ischemic optic neuropathy, patients commonly have diabetes, hypertension, and hyperlipidemia, but any thrombotic condition capable of producing intracranial stroke can affect the ciliar arteries as well.
The triggering factor for an attack of acute ischemic neuropathy even in the presence of arterio-sclerosis of other recognizable cardiovascular anomaly is rarely identified. Management, therefore, presents complicated problems because ischemic optic neuropathy is not a diagnosis but a recognition of local anoxia of the anterior region of the optic nerve and the causes are both multiple and complex.