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Purpose: To investigate the potential use of mfERG as an objective functional test that can express inner and outer retinal changes during the early stages of glaucoma. Methods: One hundred and twenty-six eyes of 126 patients were included. There were 30 healthy (Group 1), 28 glaucoma suspect (Group 2), 48 early glaucoma (Group 3), and 20 advanced glaucoma cases (Group 4). After complete ophthalmic examination, Humphrey visual field analysis and mfERG were performed. These examinations were performed three times at 6-month intervals, and only the last examination results were used for the analysis. Visual fields global indices and mfERG implicit time and amplitudes were evaluated and analyzed by ring system (central 5°, 5°-10°, 10°-15° and >15°). One-way ANOVA and ROC curve analysis were used for statistical analysis. Results: There was no statistically (one-way ANOVA) significant differences in patient age between groups ( p = 0.126). For all rings, we detected statistically significant differences for the mean implicit time (latency) of the N1, P1, and N2 components between the advanced glaucoma and control subjects and between the advanced glaucoma and glaucoma suspects. The N2 amplitudes were significantly decreased in all rings in the advanced glaucoma patients when compared with control subjects. The N2 amplitude was significantly different between healthy subjects (Group 1) and early glaucoma subjects (Group 3) in the central 2° and 2°-5° rings. We used MedClac ROC curve analysis to identify the best parameters for discriminating between control subjects (Group 1) and early glaucoma patients (Group 3). The N2 implicit time for the central 2° ring ( p < 0.0001), N2 amplitude for the central 2° ring ( p = 0.0001), P1 implicit time for the 2°-5° ring ( p = 0.0001), N2 implicit time for the 2°-5° ring ( p = 0.0003), and N2 amplitude for the 2°-5° ring ( p = 0.001) had ≥0.7 AUC values and were the best parameters in the ROC curve analyses that included the VFA parameters Conclusion: Alterations of amplitudes and implicit times of N2 response in the central area may be able to detect glaucoma earlier than VFA. In addition, with progression to advanced glaucoma these changes can be significant in all retinal areas. Although implicit times of all mfERG components are significantly delayed in glaucoma, both delayed implicit time and decreased amplitude of N2 wave in the central area are effective predictors in early glaucoma diagnosis. [ABSTRACT FROM AUTHOR]