One hundred eighty-four glaucomatous eyes (125 patients) with visual field defects of Stage I and II in the central visual field were examined with the Octopus perimeter 201, Program 31 or 33, and were divided into 3 groups according to maximum intraocular pressures: (1) low-tension glaucoma (21 mm Hg), (2) glaucoma simplex (22-29 mm Hg), (3) glaucoma simplex (30-39 mm Hg). In these three groups of glaucomatous eyes the cupping of the optic disk, vision and blood pressure were examined and a further check for cardiovascular risk factors was carried out by the internist. All three groups proved to have an equally high incidence of cardiac insufficiency, abnormal EKG changes and diabetes. However, a low systolic blood pressure was found to be the risk factor more often in patients with low-tension glaucoma than with glaucoma simplex. Furthermore, intraocular pressures in the low-tension glaucoma group were higher than those in the normal population. The occurrence of cupping of the optic disk, which is not present with purely vascular optic nerve diseases, and the location of visual field defects in low-tension glaucoma, which is similar to that in glaucoma simplex but different from vascular diseases, as well as the increased diurnal tension variations of diurnal tension curves compared to the normal population are all factors which indicate that low-tension glaucoma is not a purely vascular optic nerve disease, and that pressure-lowering therapy is necessary.(ABSTRACT TRUNCATED AT 250 WORDS)