Factors Associated With Progression to Primary Angle Closure

Importance: Identifying primary angle closure suspect (PACS) eyes at higher risk of progressing to primary angle closure (PAC) is clinically important. Objective: To evaluate baseline anterior segment risk factors associated with progression from PACS to PAC over 5 years. Design, Setting, Participants: This post hoc analysis involves data from a randomized clinical trial (Singapore Asymptomatic Narrow Angles-Laser Iridotomy Study) conducted at 5 tertiary eye hospitals from November 1, 2004, to October 31, 2018. The original enrollment included 480 participants. Data analysis for this report was conducted from May to July 2025. Interventions: All participants underwent comprehensive ocular examinations, including anterior segment optical coherence tomography (AS-OCT) and ultrasound biomicroscopy (UBM) at baseline, before laser peripheral iridotomy (LPI), and LPI in 1 randomly selected eye. PACS was diagnosed if the pigmented trabecular meshwork was not visualized for 2 or more quadrants on nonindentation gonioscopy. Main Outcome and Measures: Progression was defined as development of PAC (intraocular pressure [IOP] >24 mm Hg and/or ≥1 clock hour of peripheral anterior synechiae, or an episode of acute angle closure). Risk factors for progression were assessed using univariable and multivariable generalized linear models (GLMs) with generalized estimating equations and Cox regression models clustered by participant. We estimated odds ratios (ORs) with 95% CI using GLM and hazard ratios (HRs) with 95% CI using Cox regression. Results: Of the 480 participants originally enrolled, 161 (33.5%) underwent baseline AS-OCT and UBM. Among these participants, 123 (76.4%) were female and 38 (23.6%) male; the mean (SD) age was 62.9 (7.2) years. Overall, 16 of 322 eyes (5.0%, 7 with LPI and 9 without LPI) progressed. In the multivariable GLM model (area under the receiver operating characteristic curve = 0.83), higher baseline IOP (OR, 1.6 per 1 mm Hg; 95% CI, 1.2-2.1; P = .003) or a higher number of plateau iris quadrants on UBM (OR, 4.5 per quadrant; 95% CI, 1.6-13.0; P = .005) were associated with progression. In the multivariable Cox model adjusted for baseline IOP, trabecular-iris space area (TISA750; HR, 3.1 per -0.1 mm2; 95% CI, 1.3-7.5; P = .02) or the presence of plateau iris in ≥1 quadrant (HR, 11.1; 95% CI, 3.3-37.7; P = .001) were independently associated with greater risk of progression. An additional Cox model adjusting for iris curvature confirmed the associations of TISA750 (HR, 3.3; 95% CI, 1.3-8.6; P = .02) or plateau iris (HR, 12.5; 95% CI, 3.8-40.4; P < .001) with progression. Conclusions and Relevance: Narrower anterior chamber angles, plateau iris configuration in more than 1 quadrant, or higher baseline IOP were associated with greater risk of progression. Trial Registration: ClinicalTrials.gov Identifier: NCT00347178.