We reviewed the automated visual field tests of 110 nondiabetic and 87 diabetic patients with primary open-angle glaucoma randomly selected from a large glaucoma practice to investigate a possible qualitative difference in the pattern of visual field defects between nondiabetic and diabetic patients with primary open-angle glaucoma. A single reviewer analyzed, in masked fashion, the visual field tests of each patient and decided whether or not visual field defects were present mainly in the inferior half of the visual field. Of the 110 nondiabetic patients, 40 (36.4%) had visual field defects located mainly in the inferior half of the visual field in one or both eyes, whereas 56 of the 87 (64.4%) diabetic patients had such defects. This difference was statistically significant (P = .0001). We believe that a vascular factor, such as that attributable to diabetes mellitus, may influence glaucomatous optic nerve damage, thus causing a difference in the pattern of visual field loss in patients with primary open-angle glaucoma.