Some patients with nonarteritic ischemic optic neuropathy have no signs or symptoms of systemic vascular disease; therefore, nonvascular factors may play a role in the pathogenesis of this syndrome. We observed that the average cup-disk ratio of the unaffected optic disks in a group of patients with ischemic optic neuropathy was significantly (P = .005) smaller than the average ratio in a group of age-matched controls (0.36 +/- 0.19 vs 0.21 +/- 0.16). Fourteen of 30 patients but only two of 29 controls had cup-disk ratios equal to or less than 0.1. Mechanical factors, such as constriction of axons as they traverse the scleral canal, may contribute to the pathogenesis of ischemic optic neuropathy.