Objective To analysis each layer of retinal thickness， especially the ganglion cell layer （GCL） in the macular area， in patients with primary open-angle glaucoma （POAG） using an RTVue OCT； to assess its value in the diagnosis of glaucoma. Methods In this prospective case-control study， 76 patients （91 eyes） with POAG （30 patients [30 eyes] in the early stage， 25 patients [29 eyes] in the middle stage and 21 patients [32 eyes] in late stage） and 32 healthy age- and gender-matched controls （32 eyes） were recruited. The macular area was scanned with an RTVue OCT， and the retina was divided into nine layers with self-programming retinal image processing software. The thickness of each layer and the total retinal thickness were calculated and an LSD-t test was used to compare the average thickness of the macular area in each retinal layer for early， middle and late POAG patients and the control group. Results In the early stage of POAG， the mean thicknesses of the retinal nerve fiber layer （RNFL） and ganglion cell layer （GCL） were 31.6±9.2 μm and 33.9±5.0 μm， respectively， becoming thinner （P＜0.05） than healthy controls. In the middle stage， the mean thicknesses of the RNFL and GCL were 31.2±3.4 μm and 34.1±3.9 μm， respectively， which was thinner than the control group （P＜0.05）. In the late stage， the mean thicknesses of the RNFL， GCL， inner plexiform layer （IPL）， inner segment of the photoreceptor （IS）， and total retina （TR） were 18.8±7.6 μm， 24.2±7.9 μm， 38.0±6.4 μm， 22.8±4.4 μm and 299.5±15.1 μm， respectively， and all measurements were thinner than the controls （P＜0.05）. The mean thickness of the inner nuclear layer （INL） was 39.1±6.6 μm， which was thicker than the controls （P＜0.05）. Conclusion The mean thickness of the retinal macular area of POAG patients became obviously thinner. The GCL was especially affected by early POAG. GCL combined with clinical observations can be used as an early diagnostic indicator of POAG.