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Introduction: Various haemodynamic factors have been implicated as pathophysiological mechanisms in Primary Open Angle Glaucoma (POAG) other than raised Intraocular Pressure (IOP). However, the exact relationship still remains unclear. Aim: To examine the circadian pattern of Blood Pressure (BP), IOP and Ocular Perfusion Pressure (OPP) with the aim of understanding their relationships in a cohort of patients with POAG. Materials and Methods: A cross-sectional study was conducted in which 44 cases of newly diagnosed, non-hypertensive patients with POAG were enrolled and categorised based on the severity of glaucoma. Recording of BP and IOP were done every 4th hourly during a 24 hour hospital stay. The Mean OPP (MOPP) was calculated as 2/3×Mean Arterial Pressure (MAP)-IOP. Systolic OPP (SOPP) was calculated as Systolic BP-IOP and Diastolic OPP (DOPP) was calculated as Diastolic BP-IOP. The diurnal, nocturnal and 24 hour fluctuations were derived from the difference between the highest and lowest values within each period. Data was analysed using Statistical Package for the Social Sciences (SPSS) version 16.0. Univariate and multivariate regression analysis of the variables with age and severity of POAG were performed Results: Significant positive correlation of the nocturnal fluctuations in MAP (r=0.533), SOPP (r=0.835), DOPP (r =0.768), MOPP (r=0.685) and 24 hour fluctuation in MOPP (r=0.636) were noted with severity of glaucoma on multivariate analysis. No significant correlation of these parameters with age was noted on multivariate analyses. Conclusion: Nocturnal dip in OPP was an important observation among patients with POAG, potentially contributing to its pathophysiology.