Hyperopia as a risk factor for nonarteritic anterior ischemic optic neuropathy.

The most convincing morphologic component in the pathogenesis of nonarteritic anterior ischemic optic neuropathy is the anatomically small and crowded optic nerve head. Because the appearance of the optic disk is presumed to be related to underlying refractive error, we sought to determine if a particular refractive error places patients at additional risk for, or affords protection from, nonarteritic anterior ischemic optic neuropathy. We compared refractive errors of 50 patients with nonarteritic anterior ischemic optic neuropathy to an age-matched and eye-matched control population. The mean refractive error (in spherical equivalents) for the nonarteritic anterior ischemic optic neuropathy group was +0.26 diopter (SD +/- 2.08); the mean refractive error for controls was -0.86 diopter (SD +/- 2.91) (P = .027). Our results suggest that patients who have nonarteritic anterior ischemic optic neuropathy are less myopic than a control population. Whether it is myopia that protects from, or hyperopia that predisposes to nonarteritic anterior optic neuropathy, our results imply another anatomically based factor that characterizes eyes that develop nonarteritic anterior ischemic optic neuropathy. Those eyes tend to be minimally hyperopic.