There are well-known associations between systemic arterial hypertension and a variety of ocular disorders that were previously considered to be primarily manifestations of arterial hypertension. Recent studies with 24-hour ambulatory blood pressure monitoring have shown that the development and progression of nonarteric anterior ischemic optic neuropathy and glaucomatous optic neuropathy are significantly correlated with nocturnal arterial hypotension, particularly in hypertensive patients receiving oral hypertensive therapy. These studies suggest that several of the ocular or optic nerve head ischemic or ocular vascular disorders previously thought to be manifestations of arterial hypertension may, in fact, be due to a combination of systemic arterial hypertension and hypotension, with arterial hypertension acting as a predisposing factor and arterial hypotension actually producing the disorders. This paper reviews this subject in light of recent studies and discusses the physiopathologic bases of the disorders in question. With the development of potent arterial hypotensive medications for arterial hypertension, arterial hypotension (particularly nocturnal hypotension) is increasingly emerging as an important cause of visual disorders. Therefore, it is strongly recommended that when a patient is at risk for ocular or optic nerve head ischemic or ocular vascular disorders, the ophthalmologist should talk to the treating physician about the potential risks of intensive arterial hypotensive therapy, particularly that administered in the evening or at bedtime.