Diagnostic accuracy of total macular and ganglion cell layer thickness in differentiating different stages of glaucoma: an SD-OCT study

Purpose: To determine the diagnostic accuracy of mean macular retinal thickness (mRT) and macular ganglion cell layer (mGCL) thickness measured by Spectralis spectral-domain optical coherence tomography (SD-OCT) posterior pole thickness map (PPTM) in differentiating between normal and glaucoma eyes of different severity.Study design: Cross-sectional study.Methods: All subjects were divided into normal and glaucoma groups according to the visual fields-based Glaucoma Staging System. They underwent slit-lamp examination, Humphrey visual field test, and SD-OCT (PPTM) imaging. mRT and mGCL thickness measurements were recorded. Analysis of variance with the least significant difference post hoc test was used for pairwise comparison. Ability to discriminate between normal eyes and those with differing severity of glaucoma was assessed using the area under the receiver operating characteristic curve (AUROC).Results: A total of 201 eyes from 201 subjects were enrolled in this study. The mean glaucoma was 290.2 ± 12.1 μm, 270.1 ± 17.0 μm, and 259.1 ± 15.0 μm, respectively. Mean mGCL thickness for the corresponding three groups was 32.3 ± 2.8 μm, 27.6 ± 3.3 μm and 22.2 ± 3.8μm, respectively. AUROC analysis showed excellent diagnostic discrimination between glaucoma and normal subjects for mRT (AUC: 0.90) and mGCL thickness (AUC: 0.92). The cut-off value of mRT was 274.9 μm (90% sensitivity, 75% specificity) and of mGCL thickness was 27.9 μm (93% sensitivity, 74% specificity). The discrimination ability performance of mRT and mGCL thickness deteriorated with increasing severity of glaucoma with mGCL thickness (AUC: 0.67–0.87) performing slightly better than mRT for all grades (AUC: 0.58–0.71).Conclusions: mRT and mGCL thickness measurement on PPTM showed great sensitivity and specificity to discern between normal and glaucomatous subjects. The discrimination ability of mRT and mGCL thickness, however, decreases with increasing grade of glaucoma. We believe SD-OCT PPTM offers an alternative imaging method to detect early glaucoma.