Intraocular pressure, a major risk factor for glaucoma, is known to vary throughout the day, yet glaucoma continues to progress in some patients despite it being well controlled. It is important to understand how other glaucomatous risk factors are affected by circadian variations. The purpose of this review is to analyze the literature concerning circadian variations in systemic blood pressure, ocular perfusion pressure, and ocular blood flow and to identify consensus findings regarding their impact on glaucoma. This review suggests that nonphysiologic nocturnal blood pressure dipping and wider circadian fluctuations in ocular perfusion pressure are linked with the development and progression of glaucoma. No consensus concerning circadian variations in ocular blood flow exists in the current literature, and future investigations of nocturnal changes in blood flow and glaucoma progression are required.