Quantitative analysis of retinal nerve fiber layer defect in early open-angle glaucoma with normal intraocular pressure

Abstract

Purpose To quantitatively analyze the topographic features of localized retinal nerve fiber layer (RNFL) defects according to baseline intraocular pressure (IOP) level in cases of early primary open-angle glaucoma (POAG).

Study design Retrospective comparative study.

Methods POAG patients meeting the following conditions were consecutively included: (1) baseline office-hour diurnal IOP ≤ 21 mmHg, (2) 1 localized RNFL defect as observed on red-free fundus photography, and (3) corresponding visual field defect. Defects’ approximations to the macula (angle α) and width (angle ß) as well as the angle between the disc long axis and the vertical meridian line (angle Ɣ) were measured on red-free fundus photography. The corrected angle α was calculated as the difference between angles α and Ɣ. The defect area’s RNFL thickness was calculated by means of optical coherence tomography’s Advanced Extraction analysis utility.

Results Comparative analysis was performed between 2 groups: 45 eyes of 45 patients with low-teen IOP (group A: highest IOP ≤ 15 mmHg) and 49 eyes of 49 patients with high-teen IOP (group B: lowest IOP > 15 mmHg). In group A, the mean baseline IOP was lower (12.9 ± 1.3 vs 17.1 ± 1.0 mmHg; P < .001), the corrected angle α was smaller (32.4 ± 15.1 vs 39.5 ± 13.1 degrees; P = .017), and the defect area’s RNFL thickness was thinner (66.3 ± 16.8 vs 76.3 ± 14.9 μm; P = .003) than in group B; angle ß showed no intergroup difference (P = .230).

Conclusions In POAG patients with low-teen IOP relative to those with high-teen IOP, localized RNFL defects were closer to the macula. In addition, the RNFL thickness of the defect area was markedly thinner.