Ability of optical coherence tomography-determined ganglion cell complex thickness to total retinal thickness ratio to diagnose glaucoma

Abstract

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 36.0 ± 1.5% 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.