ObjectiveTo observe the incidence and risk factors of microcystic macular edema (MME) in patients with idiopathic macular epiretinal membrane (IMEM) preoperatively and postoperatively. MethodsA retrospective case series study. From January 2017 to May 2021, 72 eyes of 72 patients with IMEM in Eye Hospital of Wenzhou Medical University at Hangzhou were included. There were 18 male and 54 female. Average age was 64.8±7.8 years. Eyes were all monocular. All patients received the examination of best corrected visual acuity (BCVA) by standard logarithmic visual acuity chart, which was represented logarithmic of minimum angle of resolution (logMAR). Optical coherence tomography was used to measure central macular thickness (CMT). MME was defined as small, vertically bounded cystic space located outside the fovea in the inner layer of the retina. According to the presence or absence of MME before surgery, the affected eyes were divided into two groups: non-MME group (35 eyes) and MME group (37 eyes). The difference of logMAR BCVA and CMT was statistically significant between Group A and B (t=3.117, 2.589; P=0.003, 0.012). All patients with IMEM were treated with 23G three-channels pars plana vitrectomy (PPV) with epiretinal membrane and inner limiting membrane (ILM) peeling. The two groups were further divided into four groups according to whether there was MME in the postoperative follow-up time. The group A1 was without MME before and after surgery, group A2 was without MME before surgery and with MME after surgery. The MME group was subdivided into the group with MME before surgery and without MME after surgery (group B1) and the group with MME before and after surgery (group B2). The mean follow-up time was 8.8±7.7 months. The same equipment and methods were used to exam the patients during the follow-up. Paired t test was used to compare the changes of MME, BCVA and CMT before and after surgery. The differences of CMT and BCVA among groups before and after surgery were compared by independent sample t test and one-way ANOVA. Logistic regression was used to analyze the influencing factors of MME before and after surgery, and multiple linear regression was used to analyze the influencing factors of postoperative BCVA. ResultsThere were 35 eyes in the non-MME group, 18 eyes (51.43%, 18/35) in the A1 group and 17 eyes (48.57%, 17/35) in the A2 group, respectively. There were 37 eyes in MME group, 6 eyes (16.22%, 6/37) in group B1 and 31 eyes (83.78%, 31/37) in group B2, respectively. At last follow-up, the logMAR BCVA was 0.10±0.12, 0.25±0.17, 0.09±0.11, 0.30±0.26 in group A1, A2, B1, and B2, respectively. Compared with the logMAR BCVA before surgery, the differences were statistically significant (t=3.779, 4.253, 7.869, 6.668; P＜0.01). There was significant difference in logMAR BCVA among the four groups (F=4.460, P＜0.01). There was a significant difference in logMAR BCVA between group A1 and group A2 (t=－2.930, P=0.006). There was no significant difference between group B1 and group B2 (t=－1.921, P=0.063). The CMT of group A1, A2, B1 and B2 were 371.83±73.24, 431.24±83.13, 407.00±28.07 and 425.19±70.97 μm, respectively. Compared with those before operation, the differences were statistically significant (t=5.197, 2.465, 3.055, 6.078; P＜0.05). There was no significant difference in CMT among the four groups (F=2.597, P=0.059). Logistic regression analysis showed that pre-operation MME was correlated with pre-operation IMEM stage (β=1.494, P=0.004). New MME after surgery was correlated with age (β=0.153, P=0.013). Multiple linear regression analysis showed that postoperative visual acuity was significantly correlated with CMT before surgery and MME after surgery (β=0.001, 0.134; P=0.015, 0.019). ConclusionsPPV combined with epiretinal membrane and ILM peeling surgery for IMEM can improve visual acuity and decrease CMT. MME regress or regenerate after surgery. Age is an independent predictor of the risk of newly formed MME after surgery.