Although intraocular pressure (IOP) is considered the main risk factor for the development of glaucoma and the only parameter subject to treatment, there is sufficient evidence to suggest that glaucoma may continue to progress despite lowering patients' IOP to targeted levels. Several studies have implicated vascular risk factors in the pathogenesis of glaucoma. Among them, blood pressure (BP) and ocular perfusion pressure have become increasingly important. Although clinicians cannot currently visualise ocular blood flow directly, they can easily measure glaucoma patients' BP and IOP to calculate their ocular perfusion pressure and quantify the vascular changes. The purpose of this review article is to discuss the relationship between BP and IOP, BP and glaucoma, and perfusion pressure and glaucoma. We discuss the importance of autoregulation to maintain the adequate perfusion of the optic nerve head, and suggest that ocular perfusion pressure and its fluctuation may be parameters that need to be measured in glaucoma patients.