Comparison of localised nerve fibre layer defects in normal tension glaucoma and primary open angle glaucoma.

AIM To compare the pattern of localised nerve fibre layer (NFL) defects in normal tension glaucoma (NTG) and primary open angle glaucoma (POAG). METHODS 50 NTG eyes and 36 POAG eyes, all with localised NFL defects, were enrolled. On retinal NFL photography, the proximity of the defect to the centre of the fovea (angle alpha) and the sum of the angular width of the defects (angle beta) were determined. Angle alpha was the angle made by a line from the centre of the fovea to the disc centre and a line from the disc centre to the disc margin, where the nearest border of the defect met. The patterns of localised NFL defects in NTG and POAG were compared with angles alpha and beta. Independent t test was used for statistical analysis. RESULTS Angle alpha in NTG (35.1 (SD 20.0) degrees ) was significantly smaller than that of POAG (45.9 (21.9) degrees ) (p=0.02), while angle beta in NTG (49.0 (31.9) degrees ) was significantly larger than that of POAG (33.1 (23.9) degrees ) (p=0.01). CONCLUSIONS The pattern of NFL defects in NTG was different from that in POAG. Localised NFL defects in NTG were closer to the fovea and wider in width than those in POAG.