Early Functional Biomarkers of Idiopathic Epiretinal Membrane Progression: A 24-Month Prospective Observational Study

PURPOSE. To identify early functional biomarkers of progression in idiopathic epiretinal membrane (iERM) eyes managed conservatively, with particular emphasis on near-vision performance. METHODS. In this prospective cohort study, 60 eyes with iERM and non-cataractous phakic lenses were examined at baseline, 12 months, and 24 months. Functional assessments included distance best-corrected visual acuity (distance BCVA, logMAR), near best-corrected visual acuity (near BCVA, logMAR), reading acuity (RA), critical print size (CPS), and maximum reading speed (MaxRS), all obtained using standardized protocols. Structural imaging included spectral-domain optical coherence tomography (SD-OCT) with retinal layer segmentation and en face A-zone area quantification. Eyes were classified as non-, slow, or fast progressors based on a letter loss of ≤5, 6 to 9, or ≥10 (or surgery) in distance BCVA. Available case analyses were performed (n = 58 at 12 months; n = 52 at 24 months). RESULTS. Distance BCVA showed small mean changes at 12 months (+8.3%) and 24 months (+12.1%), reaching statistical significance only in fast progressors (P < 0.001). Near BCVA demonstrated larger variations (+16.7% at 12 months; +25.0% at 24 months), with significant worsening in slow and fast progressors. Reading measures showed earlier and more pronounced decline: RA increased by +16.7% at 12 months and +25.0% at 24 months, CPS enlarged by +21.7% and +30.4%, and MaxRS decreased by −22.4% and −35.7%, respectively, with the greatest deterioration in fast progressors. A-zone enlargement (β = 0.42, P < 0.001) and inner nuclear layer thickening (β = 0.36, P = 0.008) independently predicted CPS worsening, whereas central macular thickness and ellipsoid-zone disruption predicted distance BCVA decline. CONCLUSIONS. Near-vision parameters capture early functional deterioration in iERM more sensitively than distance BCVA or thickness-based OCT metrics. Incorporating near-vision performance into routine monitoring may improve detection of functional progression and complement longitudinal clinical monitoring.