Purpose: To comparatively evaluate the optic nerve head (ONH) using Optical Coherence Tomography (OCT) in normal subjects, primary open angle glaucoma (POAG) and chronic primary angle closure glaucoma (CPACG) patients.
Methods: A total of 138 normal eyes (138 subjects) and 139 glaucomatous eyes (139 patients), were evaluated in this cross-sectional observational study. The ONH was imaged on OCT using the optic disc scan. Disc area, cup area, rim area, vertical integrated rim area (VIRA), rim volume (horizontal integrated rim volume), average cup/disc ratio, horizontal and vertical cup/disc ratios, and cup volume were evaluated. Additionally, cup depth and slope of the temporal ONH were also measured. These ONH parameters were compared between normal subjects and eyes with early POAG and CPACG. Correlation of mean deviation and corrected pattern standard deviation on full threshold 30-2 perimetry, with measured ONH parameters was carried out amongst the two groups.
Results: There was a significant difference in disc area (2.38 +/- 0.5, 2.77 +/- 0.4, 2.62 +/- 0.4 mm(2), p < 0.01), cup area (0.88 +/- 0.6, 1.99 +/- 0.7, 1.60 +/- 0.7 mm(2), p < 0.01), rim area (1.48 +/- 0.4, 0.86 +/- 0.4, 0.96 +/- 0.4 mm(2), p < 0.01), VIRA (1.64 +/- 0.3, 1.23 +/- 0.3, 1.22 +/- 0.4 mm(2), p < 0.01), rim volume (0.34 +/- 0.2, 0.1 +/- 0.1, 0.15 +/- 0.1 mm(3), p < 0.01) and cup/disc ratio (0.36 +/- 0.2, 0.69 +/- 0.1, 0.63 +/- 0.2, p < 0.01) in normal vs POAG vs CPACG eyes respectively. A comparison of ONH parameters between early POAG and early CPACG showed a significant difference in the disc area (2.85 +/- 0.3, 2.57 +/- 0.4 mm(2), p = 0.03), cup area (2 +/- 0.5, 1.34 +/- 0.5 mm(2), p < 0.01), rim area (0.96 +/- 0.4, 1.21 +/- 0.5 mm(2), p = 0.009), rim volume (0.12 +/- 0.1, 0.18 +/- 0.1 mm(3), p < 0.01) and cup/disc ratio (0.67 +/- 0.1, 0.53 +/- 0.2, p < 0.01). The parameters with the highest area under the receiver operator characteristic (AROC) curves for differentiating normal and early POAG eyes were rim volume, 0.89, VIRA, 0.84, and rim area, 0.76. The AROC values (normal vs early CPACG eyes) were 0.75 for rim volume, 0.72 for VIRA, and 0.66 for rim area.
Conclusion: OCT may serve as a useful diagnostic modality in distinguishing a normal optic disc from a glaucomatous one, even in the early stages of glaucoma. Rim volume, VIRA and rim area can be used to differentiate normal from early glaucoma (both early POAG and CPACG), and most efficiently early POAG eyes. CPACG eyes have smaller discs, a smaller cup, smaller cup/disc ratio, and a larger rim area when compared with eyes with POAG.