Retinal Nerve Fibre Layer and Ganglion Cell Complex Measurement and their Correlation with Visual Field Changes among Glaucoma Patients

Abstract

Introduction: Glaucoma is an optic neuropathy that causes loss of Retinal Ganglion Cell (RGC) and changes in the visual field. The loss in RGC is determined by Optical Coherence Tomography (OCT), and visual field defects are evaluated with perimetry. A study of RGC loss and visual field defects together might help to detect glaucoma earlier. Aim: To determine the relationship between Retinal Nerve Fibre Layer (RNFL) and Ganglion Cell Complex (GCC) thickness measured with OCT, and visual field sensitivity evaluated with Standard Automated Perimetry (SAP) in glaucoma patients of varying severity. Materials and Methods: This was a cross-sectional study, conducted in a tertiary care hospital, Ajmer, Rajasthan from October 2018 to January 2020. Sixty glaucoma patients were recruited for ophthalmic evaluation. The two test SAP and SD-OCT were performed on all patients. Patients were categorised into three groups i.e., early, moderate and severe, based on severity. The RNFL, Mean Deviation (MD) and Pattern Standard Deviation (PSD) were compared among these three groups. One way Analysis of Variance (ANOVA) was used to compare the mean values of RNFL, GCC, MD and PSD across the three glaucoma groups. Post hoc analysis was done by Tukey’s range test. Correlation was assessed using Spearman’s correlation coefficient. Results: The mean (SD) age of participants were 54.43 (10.07) years. Total 15% of patients belonged to early stage glaucoma, 40% to moderate and 45% to severe glaucoma. The difference in mean RNFL (both superior and inferior) was found significant among the three groups. In bivariate analysis, MD was found significantly correlated with superior and inferior RNFL (r=0.70, p-value <0.01 and r=0.47, p-value <0.01, respectively). The MD was not found to correlate with superior and inferior GCC whereas, PSD was found weakly correlated with GCC superior and inferior (r=-0.26, p-value=0.04 and r=-0.27, p-value=0.03, respectively), though there was inverse correlation with both GCC superior and GCC inferior. PSD was not found to correlate with superior and inferior RNFL. Conclusion: Superior and inferior RFNL were associated with MD, an indicator of the severity of glaucoma. The RNFL thickness was the best indicator to differentiate the severity of glaucoma. Further exploration is needed to develop specific indications of RNFL and GCC measurement in the management of glaucoma.

Keywords

• optical coherence tomography
• optic neuropathy
• perimetry
• retinal ganglion cell