Macular Ganglion Cell-Inner Plexiform Layer (GCIPL) Thickness and Thinning Patterns for Differentiating Glaucomatous and Non-Glaucomatous Optic Neuropathy: A Prospective Comparative Study.

Purpose: To evaluate the diagnostic value of macular ganglion cell-inner plexiform layer (GCIPL) thickness and thinning patterns for differentiating glaucomatous optic neuropathy (GON) from non-glaucomatous optic neuropathy (NGON) using spectral-domain optical coherence tomography (SD-OCT). Patients and Methods: This prospective comparative study included 80 eyes (45 GON, 35 NGON). All participants underwent comprehensive ophthalmologic examination, standard automated perimetry, and SD-OCT imaging. GCIPL, peripapillary retinal nerve fiber layer (RNFL), and optic nerve head parameters were analyzed. Multivariable logistic regression was used to identify independent factors associated with disease classification. Diagnostic performance was assessed using receiver operating characteristic (ROC) curve analysis. Results: GCIPL thickness was significantly reduced in NGON compared with GON across all parameters (all P < 0.05). In an exploratory multivariable analysis, average GCIPL thickness per standard deviation decrease remained associated with disease classification (OR 1.22; 95% CI, 1.01-1.46; P = 0.038), whereas RNFL thickness did not. Minimum and average GCIPL thickness demonstrated good discrimination (AUC 0.878 and 0.859), with numerically higher AUCs than average RNFL thickness (AUC 0.759). Pattern analysis showed that GON predominantly exhibited focal or horizontal thinning, whereas NGON demonstrated diffuse or vertical hemispheric thinning. Conclusion: Macular GCIPL analysis provides potentially useful quantitative and pattern-based information for differentiating glaucomatous from non-glaucomatous optic neuropathy. GCIPL findings should be interpreted as an adjunct to the clinical examination, visual field testing, RNFL assessment, and neuroimaging when indicated, rather than as a stand-alone diagnostic test.