Changes of foveal avascular zone size and correlation between foveal avascular zone size and metamorphopsia before and after idiopathic macular epiretinal membrane surgery

Objective To observe the changes of foveal avascular zone (FAZ) size before and after surgery in idiopathic macular epiretinal membrane (IMEM) eyes and analyze the correlation of FAZ with metamorphopsia. Methods A retrospective case series study. From August 2016 to October 2017, 42 eyes of 38 patients affected with IMEM diagnosed in Central Theater Command General Hospital of Chinese People's Liberation Army were enrolled in this study. All the patients underwent a 25G pars plana vitrectomy (PPV) with IMEM removal and ininternal limiting membrane (ILM) peeling. The BCVA was measured using the international standard visual acuity chart, and the results were converted to the logMAR visual acuity. The severity of metamorphopsia was measured using M-charts. The FAZ areas were evaluated with OCT angiography in both the superficial and deep capillary plexus layers. The central macular thickness (CMT) were assessed with spectral-domain OCT before and after surgery. The logMAR BCVA was 0.61±0.21. The M-score was 0.66±0.38. The CMT of fovea was 337.71±57.63 μm. The FAZ areas in superficial and deep capillary plexus were 0.113±0.037 mm2 and 0.202±0.03 mm2, respectively. The differences in BCVA, M-score and FAZ area before and 1, 3, 6, 12 months after surgery were analyzed by ANOVA. The Spearman rank correlation analysis was performed to investigate the relationship between FAZ areas, visual acuity and metamorphopsia. Results At 12 month after surgery, the FAZ areas in superficial and deep capillary plexus were 0.146±0.021 mm2 and 0.240±0.019 mm2, respectively. Compared with baseline, the the FAZ areas in superficial and deep capillary plexus after surgery significantly increased (F=8.484, 14.346; P<0.001,<0.001). The postoperative logMAR BCVA 0.47±0.19, M-score 0.12±0.22 and CMT 270.60±33.27 μm were significantly improved compared with baseline (F=5.044, 17.763, 13.545; P=0.001, <0.001, <0.001). The preoperative FAZ area in superficial capillary plexus correlated negatively with preoperative M-score (r=-0.816, P<0.001); the preoperative FAZ area in deep capillary plexus correlated negatively with preoperative BCVA and M-score (r=-0.422, -0.882; P=0.005,<0.001). The postoperative FAZ area in superficial capillary plexus correlated negatively with preoperative and postoperative M-score (r=-0.791,-0.716; P<0.001,<0.001). The postoperative FAZ area in deep capillary plexus correlated negatively with BCVA and preoperative and postoperative M-score (r=-0.343, -0.330, -0.732, -0.694; P=0.026, 0.033,<0.001,<0.001). Conclusions PPV with ILM peeling can effectively restore the FAZ areas in superficial and deep capillary plexus, improve the visual acuity and metamorphopsia in patients with IMEM. Both superficial and deep plexus FAZ areas correlated negatively with metamorphopsia, and deep plexus FAZ area also correlated negatively with BCVA. Key words: Macula lutea; Membranes; Vitrectomy; Tomographyoptical coherence; Foveal avascular zone; Metamorphopsia