We evaluated factors associated with decreased or stable visual function in 72 patients with primary open-angle glaucoma and complete cupping of the optic disk who were followed up five years or more. We found a significantly lower mean (15.4 +/- 2.7 mm Hg) and peak (24.5 +/- 6.9 mm Hg) intraocular pressure in those patients whose vision remained stable vs those whose vision decreased (21.3 +/- 3.2 and 39.2 +/- 11.0 mm Hg, respectively) (t-test, P < .001). Additionally, the variance of each patient's individual intraocular pressure readings measured during the follow-up period was lower in the group with stable vision (4.5 mm Hg) than in those in whom vision decreased (9.0 mm Hg) (F test, P < .001). Stepwise discriminant analysis disclosed that mean intraocular pressure, variance of an individual's intraocular pressure measurements over time, history of argon laser trabeculoplasty, and compliance with therapy discriminated 92.9% of patients (52 of 56) whose vision remained stable and 87.5% of patients (14 of 16) whose vision decreased. Reduction of intraocular pressure and compliance with therapy are important in patients with complete glaucomatous cupping of the optic disk.