AIMS: To evaluate the visual function and foveal architecture in patients with stage 3 idiopathic epiretinal membrane (iERM). METHODS: A cross-sectional observational study included 56 eyes of 52 patients with stage 3 iERM. The patients were classified into type A ectopic inner foveal layers (EIFL) and type B EIFL based on the presence of a continuous hyporeflective band. Visual function and foveal microarchitecture were assessed in enrolled eyes. Best-corrected visual acuity (BCVA), metamorphopsia scores, retinal sensitivity and optical coherence tomography (OCT)/OCT angiography features were compared between two subtypes. RESULT: The BCVA in type A EIFL and type B EIFL was 0.22 logarithm of minimal angle of resolution (logMAR) (0.15 logMAR, 0.40 logMAR) and 0.53±0.23 logMAR, respectively (p=0.002). Type B EIFL had higher average metamorphopsia scores, especially horizontal metamorphopsia scores, than type A (p=0.013, p=0.007, respectively). Type B EIFL had worse central 2° foveal sensitivity than type A (p=0.034). Type B EIFL had thicker central foveal thickness and EIFL thickness (514.08±73.80 µm vs 444.41±56.57 µm, p=0.001
159.75±78.30 µm vs 48.44±18.37 µm, p<
0.0001
respectively). The foveal avascular zone area of type B EIFL was smaller than that of type A (0.042±0.022 mm CONCLUSIONS: Type B EIFL demonstrated significantly worse visual function than type A EIFL, along with marked differences in foveal microstructure and microvasculature. Our study complements the current staging of iERM and helps determine the optimal timing of iERM surgery.