Signs and Symptoms of Nonarteritic Anterior Ischemic Optic Neuropathy

The average age of patients with acute nonarteritic anterior ischemic optic neuropathy (NAION) is about 61 years. The visual loss occurs abruptly and without a prodromal warning, usually while the patient is asleep or within a 12-h period, and there is no associated pain or headache. The initial swelling of the optic disc subsides within 2 months, leaving a pale, atrophic appearance, which is often sectoral (most commonly located in the superior half of the disc). There is for the most part no or very little recovery of function. In about 10 to 20% of cases, there is one or more additional episodes of abrupt loss, in a descending staircase pattern, within the ensuing 2- to 3-week period after the acute onset. Later recurrences of loss in the same eye are very uncommon, but involvement of the contralateral eye can generally be expected within the subsequent 5-year period. As in other ischemic disorders, several risk factors play a role in the process. Aside from the association with systemic vascular diseases, chiefly hypertension and diabetes mellitus, morphologic anomalies of the optic disc are common. These discs are often rather small, having no physiologic cup (again, the so-called disc at risk; ■ Fig. 8.19), and fluorescein angiographic studies have found the affected discs are usually located in a watershed zone between two adjacent choroidal regions fed by separate branches of the short posterior ciliary arteries. The latter vessels are end arteries, i.e., they have no collaterals. With impaired function of the autoregulation of small-vessel blood flow, transient periods of systemic hypotension are thought to produce sufficient ischemia within the zone that includes the optic disc. The prelaminar portion of the optic disc, in turn, depends on the arterial supply of the peripapillary choroid. Relative ischemia that lasts for more than a few minutes can result in an infarction of the optic disc. This is thought to occur most commonly when the affected individual is asleep, i.e., when mean arterial blood pressure is at a minimum.

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