Some—but not all—patients with advanced stages of epiretinal membrane (ERM) develop metamorphopsia on Amsler grid testing. Using OCT, researchers are now able to understand why this symptom only affects some and not others and, potentially, how to predict it.

The research shows that ectopic inner foveal layers (EIFL), but not central bouquet abnormality (CBA), are a good indicator for metamorphopsia in patients with advanced ERMs.

The investigators studied 60 eyes of 57 patients using OCT scans and M-charts (a series of dotted lines used to determine the level of metamorphosia). The team recorded any presentations of EIFL, CBA and central foveal thickness. They found that a total of 37 and 23 eyes were diagnosed with stage 3 and 4 ERM, respectively. The mean M‐score exhibited a statistically significant correlation with EIFL and central foveal thickness, but not with CBA, according to the study. Analyzing the direction of metamorphopsia separately, both vertical and horizontal scores were significantly correlated with EIFL, but not with CBA. Although CBA was not independently associated with metamorphosia, EIFL was significantly influenced by the presence of CBA.  

“Based on the novel OCT-based grading scheme for ERMs, our results demonstrate that EIFL, but not CBA, might be considered a good indicator for metamorphopsia in patients with advanced ERMs,” the researchers concluded in their paper.