Importance: Ocular biometrics measured by anterior segment optical coherence tomography (AS-OCT) predicts progression from primary angle closure suspect (PACS) to primary angle closure (PAC), but obtaining these measurements is time intensive and requires specialized software. Iridotrabecular contact (ITC), a qualitative feature readily visible on AS-OCT images from multiple devices, offers a potentially more accessible method for risk stratification, but the association between ITC and progression to PAC is unclear.
Objective: To investigate the association of ITC presence and length on AS-OCT images with 72-month progression from PACS to PAC.
Design, setting, and participants: This was a single-center population-based retrospective cohort study using data from the prospective Zhongshan Angle Closure Prevention (ZAP) randomized clinical trial. The untreated eyes of trial participants aged 50 to 70 years with bilateral PACS were analyzed for progression to PAC, defined as development of intraocular pressure greater than 24 mm Hg, peripheral anterior synechiae, and/or acute angle closure. ITC250/500/750 was defined as angle-opening distance of 0 mm at 250, 500, and 750 µm anterior to the scleral spur, respectively. ITC less than 250 µm in length was identified by an expert grader in images without ITC250/500/750. ITC extent was defined as the number of sectors with ITC. Risk factors for progression were evaluated using age-adjusted Cox regression models. Study data were analyzed from October 2024 to April 2025.
Exposures: ITC presence and length on AS-OCT images.
Main outcomes and measures: The main outcome was 72-month progression from PACS to PAC.
Results: A total of 825 untreated eyes (791 without progression, 34 with progression) of 825 participants (mean [SD] age, 58.7 [5.0] years; 685 female [83.0%]) were eligible. In age-adjusted Cox models, ITC presence in the nasal sector was associated with greater risk of angle closure progression (hazard ratio [HR], 4.68; 95% CI, 1.80-12.17; P = .002; concordance index [C index] = 0.71). Greater ITC length in the nasal (HR, 1.64 per 250 µm in length; 95% CI, 1.23-2.20; P < .001; C index = 0.70) or superior (HR, 1.72 per 250 µm in length; 95% CI, 1.11-2.66; P = .02; C index = 0.67) sector was associated with greater risk of progression. ITC extent and cumulative gonioscopy score were not associated with progression.
Conclusions and relevance: Nasal ITC presence and nasal or superior ITC length were associated with greater risk of 72-month progression from PACS to PAC. These findings suggest qualitative detection of ITC provides a practical alternative to ocular biometric analysis for identifying high-risk PACS eyes.