OBJECTIVE The pathophysiology of glaucoma is still undisclosed. Cardiovascular hemodynamic changes are hypothesized to contribute to glaucoma. This study aimed to determine the differences in the diurnal blood pressure (BP) of patients with normal tension glaucoma (NTG), primary open angle glaucoma (POAG), and controls without glaucoma. METHODS A total of 129 patients were included in this study. The day-night average systolic and diastolic BPs, the day-night average pulse pressures (PPs), the day-night average heart rates, and the percentage of BP decline at night were obtained from the Holter devices and compared. METHODS Prospective, randomized, case-control study. RESULTS This study included 43 NTG patients (Group 1), 44 POAG patients (Group 2), and 42 healthy subjects without glaucoma (Group 3). The age (p=0.138) and sex (p=0.216) distributions between the groups were similar. The average day-night PP values of Group 1 were 49.17±9.90 and 46.07±10.84 mm Hg, respectively, while their total average PP was 48.48±9.60, their total average systolic BP was 120.02±12.65, and their night average systolic BP was 111.93±15.87 mm Hg. In Group 2, the average day and night PP values were 54.83±10.35 and 51.73±9.10 mm Hg, respectively, their total average PP was 54.00±9.87, their total average systolic BP was 126.75±11.50, and their night average systolic BP was 119.21±12.38 mm Hg. These differences were statistically significant and the corresponding p values were 0.040, 0.040, 0.037, 0.033, and 0.038. CONCLUSIONS NTG patients have low diurnal BP parameters, which may reduce their optic nerve perfusion and may be responsible for their glaucomatous visual field damage.