Objective: To investigate the role of nocturnal arterial hypotension, intraocular pressure (IOP) and heart rate in optic nerve head (ONH) ischemic disorders, and the effects of systemic factors and topical beta-blocker eye-drops on nocturnal arterial hypotension and heart rate. Methods: We investigated prospectively, by 24-hour ambulatory blood pressure (BP) monitoring and diurnal curve of the IOP, 275 white patients with anterior ischemic optic neuropathy (AION - 114), normal tension glaucoma (NTG - 131) and primary open angle glaucoma (POAG - 30). Results: Hourly average BP data analyses showed a significantly greater drop in mean diastolic BP (p < 0.009) at night in NTG than AION. Cases with visual field deterioration had significantly (p = 0.05) lower minimum nighttime diastolic BP. Arterial hypertensives on oral hypotensive therapy showed a significantly lower mean nighttime systolic BP (p = 0.006) and larger mean percentage drop in systolic (p < 0.0001), diastolic (p = 0.0009) and mean (p < 0.0001) BPs. Normotensives and hypertensives without therapy had no such difference. IOP showed no significant correlation with visual field deterioration in any of these conditions. Patients using beta-blocker eyedrops, compared with those not using them, had greater percentage drop in diastolic BP (p = 0.028), lower minimum nighttime diastolic BP (p = 0.072) and lower minimum nighttime heart rate (p = 0.002). Conclusions: Findings of our study suggest that nocturnal hypotension, by reducing the ONH blood flow below a crucial level during sleep in a vulnerable ONH, may play a role in the pathogenesis of AION and glaucomatous optic neuropathy (GON) and progression of visual loss in them. Thus, nocturnal hypotension may be the final insult in a multifactorial situation.