A comparative study of optic nerve damage between primary open angle glaucoma and normal tension glaucoma

Abstract

To investigate the differences in the characteristics of optic nerve damage in patients with primary open angle glaucoma (POAG)and normal tension glaucoma (NTG). The optic disc parameters and retinal nerve fiber layer (RNFL) of 47 eyes of 39 subjects with POAG (IOP > 24 mmHg) and 38 eyes of 32 subjects with NTG (IOP < 21 mmHg) were measured by using a Heidelberg retina tomograph II, color stereo-optic disc photographs, and an Octopus automated perimetry. (1) Rim area, rim/disc area ratios and three sectors except temporal quadrant of optic disc were significantly smaller, whereas C/D was significantly larger in patients with NTG than those of POAG. The mean RNFL thickness and RNFL cross-sectional areas at temporal/interior and temporal/superior in those with NTG were significantly (P < 0.05) smaller than those of POAG. The rim volume was significantly (P < 0.05) smaller and mean cup depth was significantly (P < 0.05) larger in patients with NTG than POAG. (2) The defect types of RNFL: RNFL diffuse loss and local defect ratio were 53.19% and 4.26% in POAG, respectively; while were 21.05% and 55.26% in NTG, respectively. The difference between the proportions of the defect type of RNFL in patients with POAG and those of NTG is statistically significant (P < 0.01). Our results demonstrate that the varieties of C/D area ratio, rim area, RNFL thickness, and defect types of RNFL with NTG and POAG indicate that the different mechanisms are involved in optic nerve damage in the two types of glaucoma.