Ability of Optical Coherence Tomography-determined Ganglion Cell Complex Thickness to Total Retinal Thickness Ratio to Diagnose Glaucoma

Purpose:To evaluate the usefulness of the spectral-domain optical coherence tomography (SD OCT)-determined ganglion cell complex thickness to total retinal thickness ratio (G/T ratio) in diagnosing glaucoma.Methods:A total of 99 eyes with primary open-angle glaucoma and 35 normal eyes were enrolled in the study. SD OCT (RTVue-100) was used to measure the macular ganglion cell complex thickness, total retinal thickness, outer retinal thickness, and circumpapillary retinal nerve fiber layer (RNFL) thickness. A new macular parameter, the G/T ratio, was also calculated. The ability of each parameter to diagnose glaucoma was examined by analyzing the area under the receiver operating characteristics curve (AUROC) and the sensitivity at fixed specificity.Results:The G/T ratio was 36.01.5% in normal eyes, 31.8 +/- 1.7% in early glaucoma, and 30.2 +/- 2.6% in advanced glaucoma. These decreases in the ratio were statistically significant. For the AUROC, the individual SD OCT parameters were 0.982 for the G/T ratio, 0.968 for the macular ganglion cell complex thickness, 0.942 for the RNFL thickness, and 0.841 for the total retinal thickness. The AUROC for the G/T ratio was significantly higher than that seen for the total retinal and RNFL thicknesses (P<0.05). Analyses of the sensitivity at a specificity of >90% indicated that the G/T ratio (sensitivity, 93.94%) was the best diagnostic parameter.Conclusions:Decreases in the G/T ratio occur during the early stages of glaucoma. When using SD OCT to diagnose glaucoma, the G/T ratio may improve the diagnostic ability of the macular parameter.