Objective To observe the change of retinal artery angle in eyes with idiopathic epiretinal membrane (ERM) and to analyze the relationship between retinal artery angle, ERM classification based on optical coherence tomography (OCT), and visual acuity. MethodsA retrospective cross-sectional clinical study. A total of 187 eyes in 187 patients diagnosed with monocular idiopathic ERM (IERM group) in Department of Ophthalmology of Zhejiang Provincial People's Hospital and the Affiliated Eye Hospital of Wenzhou Medical University at Hangzhou from November 2018 to January 2023 were included in the study. The contralateral healthy eyes were included as the control group. All patients underwent best corrected visual acuity (BCVA), fundus photography, spectral-domain OCT, OCT angiography (OCTA) and axial length (AL) measurement. BCVA examination was performed using the standard logarithmic visual acuity chart, which was converted to the logarithm of the minimum angle of resolution (logMAR) visual acuity. The foveal avascular zone (FAZ) area was measured by OCTA. The central macular thickness (CMT) was measured by spectral domain OCTaccording to the grading criteria of ectopic inner foveal layer (EIFL) was divided into stages 1 to 4 with 42, 45, 62, and 38 eyes, and the IERM group was subdivided into stage 1, stage 2, stage 3, and stage 4 groups accordingly. Image J was used to measure the retinal artery angle and the 1/2 retinal artery angle on fundus images. Multiple linear regression analysis was used to analyze the correlation between BCVA and artery angle, 1/2 artery Angle, CMT, FAZ area and AL. ResultsCompared with the control group, eyes in IERM group had worse BCVA (t=9.727), thicker CMT (t=12.452), smaller FAZ area (t=－14.329), smaller artery angle (t=－9.165) and smaller 1/2 artery angle (t=－9.549). The differences were statistically significant (P＜0.001). With the increase of IERM stage, the artery angle and 1/2 artery angle decreased significantly (F=21.763, 12.515; P＜0.001). There was no significant difference in artery angle and 1/2 artery angle between stage 1 group and stage 2 group, and 1/2 arterial angle between stage 2 group and stage 3 group (P＞0.05). There were significant differences in artery angle and 1/2 artery angle between the other groups (P＜0.05). There were significant differences in CMT and logMAR BCVA among different classification subgroups in IERM groups (P＜0.05). There was no significant difference in FAZ area between grade 3 group and grade 4 group (P＞0.05). There were significant differences in FAZ area between the other groups (P＜0.05). Correlation analysis showed that decreased artery angle (P=0.013) and increased CMT (P＜0.001) were associated with decreased BCVA. ConclusionsCompared with healthy eyes, the artery angle decreases significantly with the increase of ERM stage. Decreased retinal artery angle is associated with decreased visual acuity in IERM eyes.