Supplementary Material for: A Combined Index of Steady-state Pattern Electroretinogram and Optical Coherence Tomography improved the Detection of Early Glaucoma

Introduction: To evaluate the structure-function relationship between steady-state pattern electroretinogram (ssPERG), optical coherence tomography (OCT), and visual field (VF) tests, and to investigate indicators that enhance the detection of preperimetric and early-stage primary open angle glaucoma (POAG). Methods: In this retrospective cohort study, patients with POAG and normal subjects who underwent ssPERG, OCT, and VF tests were included. We defined the ratio of the amplitudes from 0.8° checks to 16° checks as the pattern electroretinogram ratio (PERGratio). The thickness of the macular ganglion cell inner plexiform layer and the peripapillary retinal nerve fiber layer (cpRNFL) were measured using spectral-domain OCT. We compared the areas under the receiver operating characteristic curves (AUCs) for ssPERG, OCT, and VF test parameters. A combined index using structural and functional measures was generated using logistic regression models to improve diagnostic accuracy. Results: Four parameters had AUCs higher than 0.8; PERGratio (AUC = 0.890), average cpRNFL thickness (AUC = 0.827), 7 o’clock cpRNFL thickness (AUC = 0.844), and inferior quadrant cpRNFL thickness (AUC = 0.830). The new index, which combines the PERGratio and 7 o’clock cpRNFL thickness, significantly improved diagnostic accuracy (AUC = 0.951), outperforming the best four parameters (all P ≤ 0.004). Furthermore, the combined index of PERGratio and 7 o’clock cpRNFL thickness showed significantly higher diagnostic accuracy compared to those combining the 7 o’clock cpRNFL thickness with visual field mean deviation, pattern standard deviation, and visual field index. Conclusion: Combined index of ssPERG, indicative of RGC dysfunction, and the OCT test, indicative of focal structural damage, improved the detection of patients with POAG in its early stage.