Several vascular factors, including systemic hypertension (or high blood pressure [HBP]), ocular perfusion pressure, and nocturnal hypotension, have been identified as risk factors for the development and progression of glaucoma. The results of epidemiologic studies of these factors and their relationships to intraocular pressure (IOP) and open-angle glaucoma (OAG) have been contradictory. Inconsistent definitions of HBP and OAG, inconsistent design, and differing population characteristics within these studies have obfuscated definitive conclusions. Here, we review the relationships among blood pressure, IOP, and OAG.