Purpose: The clinical course of reduced visual acuity, metamorphopsia, and aniseikonia are dissimilar in patients with an epiretinal membrane (ERM). We measured and compared the best-corrected visual acuity (BCVA), metamorphopsia, and aniseikonia of patients with ERM. Methods: We measured metamorphopsia and aniseikonia horizontally as well as vertically with the M-CHART (MH and MV) and New Aniseikonia Test (NATH and NATV) in 61 patients with unilateral idiopathic ERM. We compared the BCVA with the other values. Comparisons between the MH and the NATV and between the MV and the NATH were performed, because the MH assesses vertical metamorphopsia, and the MV, horizontal metamorphopsia. Results: BCVA was not significantly correlated with the other values (MH vs BCVA: P =.69; MV vs BCVA: P =.114; NATH vs BCVA: P =.656; NATV vs BCVA: P =.935). The MH and NATV magnitudes were significantly correlated, but the correlation coefficient was small (P =.007, r = 0.343); no significant correlation was found between the MV and NATH magnitudes (P =.065). We found patients with aniseikonia, but no metamorphopsia (n = 6), and more patients with metamorphopsia, but no aniseikonia (n = 11). Only 23 patients had coincident directions of metamorphopsia and aniseikonia. Conclusions: The magnitudes of metamorphopsia and aniseikonia were not closely correlated and their directions did not coincide in most patients. Neither the M-CHARTS nor the NAT measurements correlated with the BCVA. Quantitative testing of metamorphopsia and aniseikonia in addition to that for BCVA is necessary to assess visual function in patients with ERM.
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