Objective:To evaluate the risk factors for the complexity and surgical prognosis in patients with proliferative diabetic retinopathy (PDR).Methods:A historical cohort study of the CONCEPT trial, including 97 patients (97 eyes) who were diagnosed with PDR and requiring three-channel 23-gauge transconjunctival pars plana vitrectomy (PPV) from June 2017 to January 2018 at the First Affiliated Hospital of Nanjing Medical University.All patients received preoperative intravitreal injection of 0.5 mg conbercpet.Based on the PDR complexity score, patients were divided into >3 group or ≤3 group, and the systematic risk factors were compared between the two groups.The influence of sex, age, hypertension, renal insufficiency, duration of diabetes mellitus, and hemoglobin A1c level on the PDR complexity score was evaluated by multivariate logistic regression analysis.Based on age, patients were divided into <45 years group, 45-<60 years group, and ≥60 years group, and the differences in mean operative time, incidence of intraoperative hemorrhage, surgically induced lacrimation and silicone oil filling, and incidence of hemorrhage on color fundus photos and macular edema by optical coherence tomography at postoperative months 1 and 6 were analyzed among different age groups.This study adhered to the Declaration of Helsinki.The study protocol was approved by the Ethics Committee of The First Affiliated Hospital of Nanjing Medical University (No.2017-SR-283).Written informed consent was obtained from each subject.Results:The age of patients with PDR complexity score >3 was 46.5(36.0, 51.8) years, which was less than 54.0(45.5, 61.5) years for PDR complexity score ≤3, and the difference was statistically significant ( Z=1.835, P=0.002).Among the factors predicting PDR complexity score >3, logistic regression analysis indicated that only age was statistically significant ( P=0.005).For each 1-year increase in age, the risk of PDR complexity score >3 would increase by 7.4%( OR: 0.929, 95% CI: 0.883-0.977).Among the systemic factors, there were significant differences in age, history of diabetes, proportion of patients with hypertension and renal insufficiency among the three age groups (all at P<0.05).Among the ocular factors, there were significant differences in the proportion of patients with history of retinal laser treatment, fibrovascular membrane and complexity score >3 among the three groups (all at P<0.05).The proportion of patients with fibrovascular membrane and complexity score >3 in the <45 years group was significantly higher than that in the 45-<60 and ≥60 years groups (all at P<0.05).There were significant differences in the proportion of patients with intraoperative bleeding and silicone oil filling in the three age groups (all at P<0.017).The proportion of intraoperative bleeding and silicone oil filling in <45 years group was significantly higher than that in 45-<60 and ≥60 years groups (all at P<0.05).The macular edema on postoperative month 1 in the <45 years old group was significantly higher than that in the 45-<60 and ≥60 years groups (both at P<0.05). Conclusions:Among systemic factors, age has a significant impact on the increased PDR complexity and contributes to the poor prognosis of patients.There is a higher percentage of intraoperative complications and early postoperative macular edema in patients in the younger age group compared to the older age group.