Post-surgical management of epiretinal membrane (ERM) can indeed be challenging due to the approximately 70% of patients who still experience a degree of metamorphopsia after membrane removal. Prior studies have shown that improvement in postoperative metamorphopsia depends on easing tangential traction, but is complicated by pathology from traction itself. Therefore, timing of surgery becomes important.

An investigation published in Retina establishes that maximum depth of retinal folds (MDRF) can be a useful quantitative biomarker for metamorphopsia, and a specific MDRF range may indicate optimal timing for ERM removal to preserve vision above the point of impacting daily life. This observational chart review examines 172 eyes of 160 consecutive patients who were treated at a university hospital or eye clinic in Japan between June 2017 and November 2019. ERM cases were idiopathic, rather than secondary to other ocular disorders. The study used M-CHARTS (Inami & Co., Ltd.) to assess metamorphopsia, and swept-source optical coherence tomography (SD-OCT) to image retinal folds.

Of the sample, 74 eyes of 72 participants (mean age 68.1±8.3 years) underwent vitrectomy with ERM and internal limiting membrane peeling — 63 eyes also received cataract surgery. Significant correlations emerged between preoperative mean M-CHARTS score and preoperative MDRF (P <.001), as well as 6-month postoperative M-CHARTS score with preoperative MDRF (P <.001).

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M-CHARTS score of <0.5 signifies no noticeable interference with daily visual tasks. When the pre-procedure MDRF coincided with a metamorphopsia of 0.5, as gauged by the correlation between MDRF and M-CHARTS score, the resulting preoperative MDRF value was 69 μm, the study explains. Then taking the pre-surgical MDRF value that matched a post-surgical M-CHARTS score of 0.5, the result was 118 μm. Therefore, peak timing for ERM removal may be when MDRF measurement is from 69 μm to 118 μm, according to the analysis.

Investigators discovered an association between stages of ERM and preoperative MDRF. For 146 eyes of 139 individuals (mean age 69.6±8.5 years) starting MDRF was significantly deeper in patients with stage 3 and 4 ERM compared with those at stage 1 or 2 (both P <.001). Further, postoperative changes in MDRF and metamorphopsia also trended similarly. The mean MDRF of 88.3±37.8 μm decreased to 0 μm by 1 month after the procedure, and held steady at the 6-month mark. In comparison, M-CHARTS score of 0.7±0.5 resolved to 0.4±0.5 at 1 month, and remained almost the same by 6 months at 0.4±0.4. Notably, 68.9% of eyes experienced a degree of lingering metamorphopsia with severity at 54.5% of the preoperative level.

Researchers explored whether displacement of retinal vessels after ERM removal were prompted by smoothing of folds — 27 retinal fold clusters were evaluated in 12 participants (mean age 66.8±7.6 years) revealing a significant correlation between total retinal fold depth change and retinal vessel displacement (P =.013). 

Limitations of this study included its somewhat small sample, short follow-up time and retrospective nature, as well as no examination of aniseikonia and contrast sensitivity. A number of patients differed from the main MDRF range parameter, so investigators advise clinicians to consider both metamorphopsia test score and MDRFs for assessing when to remove an ERM. A strength of this analysis is that it is first to demonstrate a potential objective biomarker for metamorphopsia, and thus improved timing for ERM surgery.


Kanzaki Y, Doi S, Matoba R, et al. Objective and quantitative estimation of the optimal timing for epiretinal membrand surgery on the basis of metamorphopsia. Retina. Published online Dec. 31, 2021. doi:10.1097/IAE.0000000000003401