Glaucoma is one of the leading causes of blindness in the United States and other industrialized countries. In fact, glaucoma is now recognized to be the number one cause of blindness in African Americans. Elevated intraocular pressure (IOP) is a common condition and is thought to be the leading risk factor for the development of open-angle glaucoma. There is conflicting evidence as to whether early medical treatment is effective in preventing or delaying the onset of glaucomatous damage in individuals with elevated intraocular pressure (referred to as ocular hypertensive individuals or glaucoma suspects). The proposed study is a long-term, randomized, multicenter, single-masked clinical trial to determine whether medical reduction of intraocular pressure prevents or delays the onset of glaucomatous optic nerve and/or visual field damage in ocular hypertensive subjects. 1,500 subjects with IOP's greater than or equal to 24 mm Hg but less than or equal to 32 mm Hg in at least one eye (IOP's greater than or equal to 21 mm HG in the fellow eye) as determined by two consecutive measurements at least 2 hours, but not greater than 12 weeks, apart and normal visual fields and optic discs in both eyes will be assigned randomly to receive stepped medical treatment to both eyes or to close observation only to both eyes. Because of this level of intraocular pressure, the subjects are considered to be at moderate risk for the development of open- angle glaucoma. The subjects will be followed twice yearly with automated, threshold, central, static perimetry (Humphrey program 30-2) and once yearly with stereoscopic optic disc photographs. The study endpoints are progressive optic disc damage and/or reproducible glaucomatous visual field loss in either eye of a patient. All visual fields and optic disc photographs will be read in masked fashion in Reading Centers. While this trial is designed to study the efficacy and safety of early medical treatment in ocular hypertension, there will be other benefits as well. This study will allow us to refine and validate estimates of risk for individual ocular hypertensive patients in a large national sample. Furthermore, this study will also determine the conversion rate of African American ocular hypertensive subjects to open-angle glaucoma. At the conclusion of this study, practitioners should be able to make reasonable estimates of risk for individual ocular hypertensive patients and determine which ocular hypertensive individuals are most likely to benefit from early prophylactic medical treatment. The Study Chairman's Office and the Data Coordinating Center will be at Washington University. The Visual Field Reading Center will be at U.C.- Davis and the Optic Disc Reading Center at Yale University. The various Clinical Centers will be chosen by the NEI using an RFA mechanism at a later time.