We evaluated macular ganglion cell asymmetry as a tool for diagnosing paracentral scotoma (PCS) in early glaucoma.This prospective study compared 58 patients with early glaucoma and PCS to 58 age-matched control individuals. All glaucomatous eyes had scotoma within the central 12 degrees of fixation and confined to one hemifield. We measured circumpapillary retinal nerve fiber layer (cpRNFL) thickness, macular ganglion cell-inner plexiform layer (GCIPL) thickness, and optic nerve head (ONH) parameters with Cirrus spectral domain optical coherence tomography. Macular ganglion cell asymmetry was expressed as the absolute differences and the ratios between the inferior and superior hemispheres, inferotemporal (IT) and superotemporal (ST) areas, IT and superonasal (SN) areas, IT and inferonasal (IN) areas, and ST and IN areas. The asymmetry index was the absolute log10 of the ratio. The area under the receiver operating characteristics curve (AUROC) and partial AUROC (pAUROC, specificities ≥90%) were analyzed for each parameter.All GCIPL parameters and most cpRNFL parameters were significantly lower in early glaucoma than in controls. The best discriminating parameters were inferior RNFL thickness, average RNFL thickness, and minimum GCIPL thickness. The macular ganglion cell asymmetry parameters with the largest AUROCs were the log IT/ST index, the absolute difference in IT-ST GCIPL thicknesses, and the log IT/SN index. Performance was comparable between the log IT/ST index and the cpRNFL (inferior RNFL thickness, P=0.129), GCIPL (minimum GCIPL thickness, P=0.358), and ONH parameters (vertical cup-to-disc ratio, P=0.475).The IT/ST asymmetry index may be useful as a new parameter for detecting structural changes in glaucoma patients with PCS.