Purpose: The aim was to evaluate the value of multifocal electroretinogram (mfERG) and optical coherence tomography (OCT) in predicting post-operative visual acuity (post-VA) after removal of an idiopathic epiretinal membrane (ERM). Methods: Fifty-one eyes of 51 patients with an idiopathic macular ERM were examined by OCT and mfERG before three-port pars plana vitrectomy with removal of the ERM. The parameters of the OCT images and mfERGs, pre-operative visual acuity (pre-VA) and the duration of symptoms (DS) were compared with the post-VA. Results: The pre-VA (r = 0.570, p < 0.001) and the duration of the symptoms (r = 0.389, p < 0.035; n = 35) were significantly correlated with the post-VA. The central retinal thickness (CRT) was significantly correlated with the pre-VA (r = 0.379, p < 0.01) and the post-VA (r = 0.318, p < 0.03). The amplitudes of macular electroretinogram (amERGs) were not significantly correlated with the pre-VA or post-VA. The CRT to amERG ratio (CRT/amERG) was correlated with the post-VA (r = 0.429, p < 0.002) but not with the pre-VA (p > 0.1). Comparative analyses among groups of cases based on CRT/amERG showed significant differences in the post-VA but not in the pre-VA and the duration of symptoms. Conclusion: As with the large CRT/amERG, the pre-operative morphologically thickened and electroretinographically reduced retinas have a greater likelihood of being affected by the irreversible photoreceptor damages that could have been masked or modified by other factors before the removal of the ERM. Because the CRT/amERG values are obtained objectively, they should be valuable in predicting the post-operative visual function along with the pre-VA and the duration of symptoms.
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