| Introduction: Glaucoma is a chronic, progressive optic neuropathy characterised by degeneration of retinal ganglion cells (RGCs) and their axons, leading to characteristic visual field defects and irreversible blindness if untreated. Traditionally, glaucoma diagnosis and monitoring relied on functional assessment using standard automated perimetry. However, structural changes in the retinal nerve fibre layer (RNFL) and ganglion cell layer (GCL) precede detectable visual field loss Methodology: A hospital-based cross-sectional observational study was conducted at KLE’s Dr. Prabhakar Kore Hospital, Belagavi, over one year (April 2023–March 2024). Thirty-four patients with POAG aged over 18 years underwent a detailed ocular examination and SD-OCT imaging. RNFL and GC-IPL thicknesses were measured in superior and inferior quadrants. Statistical analyses included ANOVA, Spearman’s correlation, and post-hoc tests. Results: Spectral-domain optical coherence tomography (SD-OCT) revealed significant thinning of the peripapillary retinal nerve fibre layer (RNFL) with increasing severity of glaucoma. The superior RNFL thickness was recorded as 118 ± 15 µm in early glaucoma, 80 ± 24 µm in moderate glaucoma, and 92 ± 29 µm in advanced glaucoma. Assessment of macular ganglion cell layer (GCL) thickness showed a declining trend across the severity spectrum. Conclusion: The integration of SD-OCT parameters into clinical evaluation enhances diagnostic precision, enables earlier detection of structural alterations preceding visual field loss, and facilitates better risk stratification and disease management.