Global and sectoral retinal nerve fiber layer thickness in glaucoma suspects and primary open-angle glaucoma patients attending a tertiary care center in South India

Background: Spectral-domain optical coherence tomography (OCT) can identify the presence of localized glaucomatous structural damage. The peripapillary retinal nerve fiber layer (RNFL) thickness is a popular OCT parameter used for glaucoma diagnosis and monitoring progression. Aim: To measure the peripapillary RNFL thickness, the pattern of RNFL defect, and association of RNFL with the severity of glaucoma using Spectralis Spectral Domain – OCT in patients with primary open-angle glaucoma (POAG) at a glaucoma clinic in a tertiary care teaching hospital in south India. Methods: Cross-sectional study design. Peripapillary RNFL thickness of 109 glaucomatous eyes of 56 patients aged 40–75 years having POAG, ocular hypertension, or suspected to have glaucoma but without visual field (VF) defects were included in the study. The cross-sectional thickness of RNFL using a 3.46 mm circle centered around the disc in 6 segments were measured and defects in the RNFL were identified by comparing measurements from each patient with the normative database. Results: The study included 109 eyes with 51 (46.79%) preperimetric eyes and 58 (53.21%) POAG eyes (with field defects). The average global thickness in the study population was 91.31 ± 12.81 μm for preperimetric eyes and 67.76 ± 17.33 μm for eyes with glaucoma. There was significant thinning in all segments between eyes with POAG and normal eyes with the mean difference highest in the inferotemporal segment (mean difference of 73.05) and the superotemporal segment (mean difference of 55.85). The global RNFL thickness had a coefficient of − 0.015 (standard error [SE] 0.003, 95% confidence interval [CI]: −0.02–−0.009, R2 = 0.29) for mild glaucoma, −0.010 (SE 0.004, 95% CI: −0.02–−0.003, R2 = 0.12) for moderate and − 0.18 (SE: 0.001, 95% CI: −0.022–−0.014, R2 = 0.60) for severe glaucoma compared to preperimetric eyes in a linear regression model that adjusted for age and gender. Global and sector-wise RNFL thickness also had a significant area under Receiver Operator Characteristic (0.84, 95% CI: 0.78. 0.91) that showed the ability to discriminate between preperimetric and glaucomatous eyes. Possible “floor effect” of RNFL thickness was shown by 7 eyes with advanced glaucoma cases. Conclusion: RNFL thinning can be used as a parameter to assess glaucomatous structural loss that can aid in early diagnosis and monitoring of disease progression, to grade the severity of the disease in primary open-angle glaucoma, and when VFs cannot be done.