BACKGROUND: Primary angle-closure glaucoma (PACG) is characterized by a rise in intraocular pressure (IOP) secondary to aqueous outflow obstruction, with relative pupillary block being the most common underlying mechanism. There is increasing evidence that lens extraction may relieve pupillary block and thereby improve IOP control. As such, comparing the effectiveness of lens extraction against other commonly used treatment modalities can help inform the decision-making process. OBJECTIVES: To assess the effectiveness of lens extraction compared with other interventions in the treatment of chronic PACG in people without previous acute angle-closure attacks. SEARCH METHODS: We searched CENTRAL, MEDLINE, Embase, one other database, and two trials registers (December 2019). We also screened the reference lists of included studies and the Science Citation Index database. We had no date or language restrictions. SELECTION CRITERIA: We included randomized controlled trials (RCTs) comparing lens extraction with other treatment modalities for chronic PACG. DATA COLLECTION AND ANALYSIS: We followed standard Cochrane methodology. MAIN RESULTS: We identified eight RCTs with 914 eyes. We obtained data for participants meeting our inclusion criteria for these studies (PACG only, no previous acute angle-closure attacks), resulting in 513 eyes included in this review. The participants were recruited from a diverse range of countries. We were unable to conduct meta-analyses due to different follow-up periods and insufficient data. One study compared phacoemulsification with laser peripheral iridotomy (LPI) as standard care. Participants in the phacoemulsification group were less likely to experience progression of visual field loss (odds ratio [OR] 0.35, 95% confidence interval [CI] 0.13 to 0.91; 216 eyes; moderate certainty evidence), and required fewer IOP-lowering medications (mean difference [MD] -0.70, 95% CI -0.89 to -0.51; 263 eyes; moderate certainty evidence) compared with standard care at 12 months. Moderate certainty evidence also suggested that phacoemulsification improved gonioscopic findings at 12 months or later (MD -84.93, 95% CI -131.25 to -38.61; 106 eyes). There was little to no difference in health-related quality of life measures (MD 0.04, 95% CI -0.16 to 0.24; 254 eyes; moderate certainty evidence), and visual acuity (VA) (MD 2.03 ETDRS letter, 95% CI -0.77 to 4.84; 242 eyes) at 12 months, and no observable difference in mean IOP (MD -0.03mmHg, 95% CI -2.34 to 2.32; 257 eyes; moderate certainty evidence) compared to standard care. Irreversible loss of vision was observed in one participant in the phacoemulsification group, and three participants in standard care at 36 months (moderate-certainty evidence). One study (91 eyes) compared phacoemulsification with phaco-viscogonioplasty (phaco-VGP). Low-certainty evidence suggested that fewer IOP-lowering medications were needed at 12 months with phacoemulsification (MD -0.30, 95% CI -0.55 to -0.05). Low-certainty evidence also suggested that phacoemulsification may have improved gonioscopic findings at 12 months or later compared to phaco-VGP (angle grading MD -0.60, 95% CI -0.91 to -0.29; TISA500 MD -0.03, 95% CI -0.06 to -0.01; TISA750 MD -0.03, 95% CI -0.06 to -0.01; 91 eyes). Phacoemulsification may result in little to no difference in best corrected VA at 12 months (MD -0.01 log MAR units, 95% CI -0.10 to 0.08; low certainty evidence), and the evidence is very uncertain about its effect on IOP at 12 months (MD 0.50 mmHg, 95% CI -2.64 to 3.64; very low certainty evidence). Postoperative fibrin reaction was observed in two participants in the phacoemulsification group and four in the phaco-VGP group. Three participants in the phaco-VGP group experienced hyphema. No data were available for progression of visual field loss and quality of life measurements at 12 months. Two studies compared phacoemulsification with phaco-goniosynechialysis (phaco-GSL). Low-certainty evidence suggested that there may be little to no difference in mean IOP at 12 months (MD -0.12 mmHg, 95% CI -4.72 to 4.48; 1 study, 32 eyes) between the interventions. Phacoemulsification did not reduce the number of IOP-lowering medications compared to phaco-GSL at 12 months (MD -0.38, 95% CI -1.23 to 0.47; 1 study, 32 eyes; moderate certainty evidence). Three eyes in the phaco-GSL group developed hyphemas. No data were available at 12 months for progression of visual field loss, gonioscopic findings, visual acuity, and quality of life measures. Three studies compared phacoemulsification with combined phaco-trabeculectomy, but the data were only available for one study (63 eyes). In this study, low-certainty evidence suggested that there was little to no difference between groups in mean change in IOP from baseline (MD -0.60 mmHg, 95% CI -1.99 to 0.79), number of IOP-lowering medications at 12 months (MD 0.00, 95% CI -0.42 to 0.42), and VA measured by the Snellen chart (MD -0.03, 95% CI -0.18 to 0.12). Participants in the phacoemulsification group had fewer complications (risk ratio [RR] 0.59, 95% CI 0.34 to 1.04), and the phaco-trabeculectomy group required more IOP-lowering procedures (RR 5.81, 95% CI 1.41 to 23.88), but the evidence was very uncertain. No data were available for other outcomes. AUTHORS' CONCLUSIONS: Moderate certainty evidence showed that lens extraction has an advantage over LPI in treating chronic PACG with clear crystalline lenses over three years of follow-up; ultimately, the decision for intervention should be part of a shared decision-making process between the clinician and the patient. For people with chronic PACG and visually significant cataracts, low certainty evidence suggested that combining phacoemulsification with either viscogonioplasty or goniosynechialysis does not confer any additional benefit over phacoemulsification alone. There was insufficient evidence to draw any meaningful conclusions regarding phacoemulsification versus trabeculectomy. Low certainty evidence suggested that combining phacoemulsification with trabeculectomy does not confer any additional benefit over phacoemulsification alone, and may cause more complications instead. These conclusions only apply to short- to medium-term outcomes; studies with longer follow-up periods can help assess whether these effects persist in the long term.