AIM: To compare surgical efficacy based on residual peripheral anterior synechiae (PAS) extent after viscogonioplasty (VGP) combined with phacoemulsification and intraocular lens implantation (PEI) in patients with primary angle-closure disease (PACD) and identify risk factors for extensive postoperative PAS. METHODS: This prospective cohort study included 73 eyes of 61 patients with PACD undergoing PEI with VGP. Patients were divided into Group A (PAS<90°, n=39) and Group B (90°≤PAS≤180°, n=34) based on PAS extent at the end of surgery. PAS progression rates were assessed using a linear mixed-effects model. Logistic regression analyzed risk factors for PAS≥180° at 12mo postoperatively. RESULTS: Both groups showed significant PAS progression at 12mo (P<0.001). Group A had smaller PAS extent than Group B at all time points (P<0.001). PAS progression rates were similar between groups (P=0.335). No significant differences were found in intraocular pressure (IOP), IOP-lowering medications, or surgical success rates (P>0.05). Female [odds ratio (OR)=0.211, P=0.046], preoperative medication number (OR=1.017, P=0.029), and PAS extent at the end of surgery (OR=1.017, P=0.018) were risk factors for PAS≥180° at 12mo. CONCLUSION: Residual PAS extent at the end of surgery predicts postoperative extensive PAS formation but has limited effect on PAS progression rate and IOP control. Female, multiple preoperative IOP-lowering medications, and larger residual PAS extent are independent risk factors for extensive PAS at 12mo postoperatively.