OBJECTIVE To determine the discriminating ability of retinal nerve fiber layer (RNFL) thickness measured with spectral-domain optical coherence tomography (SD-OCT) in different stages of glaucoma. METHODS Thirty normal, 150 glaucomatous eyes were included. Glaucomatous eyes were graded into early, moderate and severe stages according to one of the global indices called visual field index (VFI). Complete ophthalmic examination, white on white perimetry and SD-OCT were done for all patients. RNFL thickness of quadrants and average thickness were recorded. Area under receiver operating characteristic curves (AUCs) were used to assess the performance of OCT parameters. RESULTS AVERAGE, INFERIOR AND SUPERIOR RNFL THICKNESS WERE THE BEST PARAMETERS TO DISCRIMINATE NORMAL FROM EARLY GLAUCOMA (AUC: 0.91-86), early from moderate (AUC: 0.77-0.70) and moderate from severe (AUC: 0.85-83). Average RNFL loss was 18% in early glaucoma, 28% in moderate glaucoma and 41% in severe glaucoma. Early damage tends to be focal and in the lower quadrant. A significant correlation was detected between mean VFI and mean RNFL loss. Glaucoma was restaged according to average RNFL loss into early: ⩾97.5 μ, moderate: <97.5-72.5 μ and severe: <72.5 μ. CONCLUSIONS RNFL thickness measured with SD-OCT could discriminate the three stages of glaucoma. RNFL loss can be correlated to visual field loss. Future OCT-based staging of glaucoma, adjunctive to perimetry is possible.