Primary open-angle glaucoma (POAG) is one of the leading causes of blindness in the United States and many other nations and is the leading cause of blindness in African Americans. Elevated intraocular pressure (ocular hypertension or OHT) is a major risk factor for developing POAG and the only modifiable risk factor at present. 4-7% of the United States population above age 40 has OHT. A major public health issue is how to apply the principles of patient- centered care and manage this large group of people in an effective and cost-effective manner. The OHTS carefully followed OHT participants for a median of 13 years (OHTS Phase 1 and 2). This includes 279 participants who developed POAG during the study, the largest inception cohort of POAG patients ever described. We propose to re-examine all surviving OHTS participants at 20 years or more in 2015-2017 (OHTS Phase 3). We will determine the incidence and severity of POAG in the OHTS cohort and determine the frequency and severity of self-reported functional limitations associated with POAG. We will also develop a 20-year prediction model for stratifying OHT patients by their risk of developing POAG and, among those who developed POAG, a prediction model for the rate of visual field loss. OHTS Phase 3 will allow us to develop evidence-based, 20-year guidelines for the management of patients with OHT. This will aid patients and clinicians to make informed decisions about the appropriate frequency of examinations and tests and the benefit of early, preventative treatment. Informed decisions should improve outcomes, reduce costs and reduce patient and clinician burden.