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The purpose of the study was to evaluate retinal vessel diameter in age-matched normal tension glaucoma (NTG) and primary open angle glaucoma (POAG) eyes with hemifield involvement.Fundus photographs of patients with hemifield defect, good visibility of retinal nerve fiber layer defect, and vessels were compared with 30 controls. One eye of each patient (28 NTG and 30 POAG) was randomly chosen for analysis using Image J software by different clinicians at 2 levels. The structural parameters analyzed included retinal nerve fiber layer defect width, diameter of vessels (superotemporal or inferotemporal artery and superotemporal or inferotemporal vein).The average superotemporal artery diameter was similar in NTG (71±16.8 µm), POAG (79±26.6 µm), and controls (82±14.1 µm), P=0.2 with similar pattern seen for other vessels. The affected quadrant in all eyes and those with disc hemorrhage (n=8) did not have significantly different arteries and veins diameter as compared with the unaffected quadrant in that eye. No relation of artery or vein diameter with retinal nerve fiber layer defect width or clinical variables in NTG or POAG eyes was seen on multivariate regression analysis.The vessel diameter was not significantly different in the affected and unaffected quadrants of age and severity-matched NTG and POAG eyes with hemifield structural and functional defect as reported in earlier studies. These results point toward the possibility that vascular diameter changes may not be the cause for glaucomatous changes.