Comparison of localized retinal nerve fiber layer defects between a low-teen Intraocular pressure group and a high-teen intraocular pressure group in normal-tension glaucoma patients

Purpose: To compare the features of localized retinal nerve fiber layer (RNFL) defects between a low-teen intraocular pressure (IOP) group and a high-teen IOP group in normal-tension glaucoma (NTG) patients. Methods: Seventy-seven eyes of 77 NTG patients showing localized RNFL defects on RNFL photographs and corresponding visual filed defects at the initial visit to a glaucoma specialist were selected for this study. Patients with range of diurnal IOP within low-teen or high-teen in both eyes were included. All participants completed refraction, diurnal IOP measurement, central corneal thickness (CCT) measurement, stereoscopic disc photography, RNFL photography, and automated perimetry. On RNFL photograph, approximation of the defect to the macula (angle alpha) and width of the defects (angle beta) were measured to represent RNFL defects. The patients were divided into 2 groups according to the level of IOP. A low-teen group had highest IOP of <= 15 mm Hg (group A) and a high-teen group had lowest IOP of > 15 mm Hg (group B). Age at diagnosis, percentage of male patients, systemic disease, refraction, CCT, highest IOP, angle alpha, angle beta, and mean deviation and pattern standard deviation of visual field were compared between the 2 groups. Results: Age at diagnosis of NTG, age distribution, percentage of male patients, systemic disease, spherical equivalent of refraction, CCT, mean deviation, and pattern standard deviation were not different between the 2 groups. Highest IOP was 13.8 +/- 1.2 mm Hg in group A and 19.2 +/- 1.4mm Hg in group B (P < 0.001). Angle a was significantly smaller in group A than in group B (37.0 +/- 14.0 vs. 56.5 +/- 21.2 degrees, P < 0.001), whereas angle (3 was not different between the 2 groups (39.9 +/- 17.9 vs. 37.5 +/- 15.9 degrees, P = 0.54). There were no significant correlations between spherical equivalent and angle alpha (r = - 0.03, P = 0.82), between spherical equivalent and angle beta (r = - 0.04, P = 0.74), and between angle alpha and angle beta (r = - 0.21, P = 0.07). Conclusions: Localized RNFL defect was closer to the center of the macula in group A than in group B, whereas width of defects was not different between the 2 groups. These findings provide indirect evidence to suggest that more than one pathogenic mechanism may exist in the development of RNFL defects in NTG.