Objectives: To compare differences in retinal nerve fiber layer (RNFL) parameters between normal subjects and patients with various degrees of glaucoma, evaluate the sensitivity and specificity of GDx-VCC parameters, and determine the capability of GDx-VCC parameters and the most valuable indicators for the diagnosis of early glaucoma. Methods: GDx-VCC was used to measure RNFL in 80 patients with early glaucoma (130 eyes), 70 patients with advanced glaucoma (90 eyes) and 40 normal controls (80 eyes). All glaucoma patients were divided into an early glaucoma group and an advanced glaucoma group, according to the mean defect of the visual field. RNFL parameters were compared between normal subjects and patients with various degrees of glaucoma. Receiver operating characteristic (ROC) curves of GDx parameters were drawn to determine the most valuable GDx parameters for the diagnosis of early glaucoma. Results: The RNFLs were significantly thinner in patients with early glaucoma than those in normal subjects; they were also significantly thinner in patients with advanced glaucoma than those in patients with early glaucoma. The differences in all parameters reached statistical significance (p < 0.001). The mean defect of the visual field was significantly correlated with all RNFL parameters (p < 0.001). The areas under the ROC curves were >0.7 for all parameters, which could effectively differentiate early glaucoma from normal subjects. The areas under the ROC curves were 0.81 for nerve fiber indicator and inferior average with better differentiation capability. Conclusions: GDx-VCC can provide quantitative measurements of RNFL thickness for clinical use, which can effectively differentiate patients with early glaucoma from normal subjects, and will be clinically very helpful for the early diagnosis of glaucoma. Nerve fiber indicator and inferior average are the most effective indicators for the early diagnosis of glaucoma.

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