The aim was to compare retinal nerve fiber layer (RNFL) and ganglion cell complex (GCC) thicknesses in patients with primary open angle glaucoma (POAG), ocular hypertension (OH) and healthy subjects, and to investigate the role of GCC parameters in glaucoma diagnosis. Eighty-one patients were divided into four groups according to Hodapp-Parrish-Anderson classification: 26 OH, 22 early POAG, 10 moderate to advanced POAG, and 23 healthy subjects. All patients underwent RNFL and GCC thickness measurement using SOCT Copernicus HR. All RNFL and GCC parameters were significantly lower in POAG than in OH and healthy subjects, especially Average RNFL, RNFL Superior and Inferior, GCC Average, and GGC Inferior. Of all RNFL parameters, the highest area under the receiver operating characteristic curve (AUC) was recorded for Average RNFL, 0.906. GCC Average, and GCC Superior and Inferior had the overall highest AUCs (0.957, 0.955 and 0.946, respectively) with 100% specificity. The RNFL Average and Inferior and GCC Average, Superior and Inferior were identified as the main predictors for development of glaucoma (p=0.015 and p=0.014 vs. p=0.002, p=0.002 and p=0.003, respectively). In conclusion, GCC parameters showed a slightly better glaucoma discriminating ability and were found to be better predictors for development of glaucoma as compared with RNFL.