Background Glaucoma is diagnosed by presence of “classical triad”- characteristic feature of visual field defects, morphological changes in optic disc (cupping) and raised intraocular pressure (IOP). Several studies related to blood pressure and ocular perfusion pressure (OPP) implicated vascular risk factors in the pathogenesis of glaucoma yet abnormal autoregulation in glaucoma is not fully clear. The most common method of evaluating autoregulatory function is through provocation like isometric head up tilt testing, which put the vascular system under stress and evoke an autoregulatory response maintaining normal ocular perfusion, a failure to this is indicative of disturbed auto regulation. Materials and methods The study subjects of age between 45-65 years of either sex comprised of 20 patients with Primary open angle glaucoma (IOP >21mmhg) (group ІІ) and 20 age and sex matched healthy controls (group І). Blood Pressure and Mean OPP was recorded at rest and immediately after relaese, then after 5minutes. MOPP was calculated as MOPP=2/3MAP – IOP. Results Mean basal MAP in group ІІ was significantly higher (104.73 ±1.45) (p=0.001) as compared to group І. The findings showed highly significant low values of basal MOPP (p<0.000) in group ІІ (POAG) compared to control group. During handgrip test the value of MAP was significantly higher and MOPP was significantly low (P<0.000) in group ІІ. The significant high value of MAP (p<0.000) and low MOPP in group ІІ during recovery period indicated delayed recovery due to sympatho-vagal imbalance. Conclusion Basal values of MAP and MOPP and changes observed during isometric exercise (stress test) and during recovery period indicated ocular vascular alterations and abnormal autoregulatory mechanism in POAG patients as compared to healthy controls.