PURPOSE: To compare the diagnostic ability of macular ganglion cell inner plexiform layer (mGCIPL) and peripapillary retinal nerve fiber layer (pRNFL) thickness on optical coherence tomography (OCT) and macular and peripapillary perfusion changes using OCT angiography (OCTA) in glaucoma suspect and early primary open angle glaucoma (POAG). METHODS: Ninety patients (30 normal, 30 glaucoma suspects, and 30 early POAG) were recruited in this cross-sectional, prospective study. The average thickness of mGCIPL and pRNFL on spectral domain-OCT and macular vessel density (VD), optic nerve head (ONH) perfusion, and ONH flux index (FI) on OCTA were evaluated for early diagnosis of glaucoma. RESULTS: Macular VD, ONH perfusion, and ONH FI were significantly reduced in early POAG eyes compared to normal. The best correlation was observed between ONH FI and the average RNFL in both glaucoma suspects ( r = 0.47, P <
0.01) and early POAG patients ( r = 0.53, P <
0.01). Out of all the measured OCTA parameters, only ONH perfusion was significantly lower in glaucomatous eyes compared to glaucoma suspects ( P <
0.001). Average GCIPL (0.82) and macular VD (0.76) had the highest area under the receiver operating characteristic (AUROC) curve value among all the OCT and OCTA parameters, respectively, for differentiating glaucoma suspects from controls. Rim area (0.92) and ONH FI (0.81) had the highest AUROC value among all the OCT and OCTA parameters for differentiating early POAG patients from controls. CONCLUSION: OCTA vascular parameters had a good correlation with structural damage both at the disc and the macula. OCT parameters were superior to OCTA parameters for diagnosis of glaucoma, although OCTA parameters are deranged very early in the disease.