Supplementary Material for: Association between ectopic inner foveal layer on optical coherence tomography and postoperative quantitative metamorphopsia in patients undergoing epiretinal membrane surgery.

Purpose: Epiretinal membrane (ERM) is a condition that can lead to visual impairment and meta-morphopsia. This study aimed to examine the correlation between metamorphopsia and foveal mi-crostructure before and after macular surgery in a cohort of patients with advanced ERM.

Methods: The severity of metamorphopsia was quantified using M-CHARTS, and foveal micro-structure was evaluated via two optical coherence tomography (OCT) measures: central foveal thickness (CFT) and ectopic inner foveal layer (EIFL). Assessments were performed pre- and post-surgery with an average follow-up of one year. Correlations between morphological and functional parameters pre- and post-surgery were explored by means of regression analysis.

Results: 60 eyes of 57 patients diagnosed with advanced ERM and surgically treated were included in the study. Our findings showed a significant correlation between postoperative metamorphopsia and both pre- (R²=0.431) and postoperative (R²=0.300) EIFL thickness. Disparities were observed in metamorphopsia scores between patients with ERM stages 3 and 4, both pre- (0.46 ± 0.31 and 0.84 ± 0.32, respectively, P<0.01) and post-surgery (0.18 ± 0.21 and 0.46 ± 0.28, respectively, P<0.01). Postoperative EIFL thickness was the only variable significantly associated with postoper-ative metamorphopsia scores according to multiple regression analysis.

Conclusion: EIFL thickness emerges as a critical determinant of postoperative metamorphopsia severity, underscoring its importance in predicting functional outcomes after ERM surgery. Although surgery improved metamorphopsia across stages, patients with more advanced ERM experienced less favorable outcomes, stressing the importance of a timely surgical intervention.