Abstract: Objective To investigate the relationship between anterior chamber angle structures assessed using ultrasound biomicroscopy (UBM) and the dark room provocative test (DRPT) in individuals with shallow anterior chambers. Design Retrospective case series. Participants A total of 70 consecutive shallow anterior chamber patients who visited the ophthalmology clinic at Xuanwu Hospital, Capital Medical University, between December 2017 and June 2019. Methods UBM imaging was performed under both well-lit and dark conditions. Anterior segment parameters were taken, including the number of positional angle closures (NPAC). Positional angle closure was categorized as L-type, B-type, or S-type based on the closure pattern. All participants underwent DRPT to assess intraocular pressure (IOP) changes, with a positive outcome defined as an IOP increase ≥8 mmHg from baseline. Correlations between the IOP change in the DRPT and various parameters assessed through UBM images were analyzed. The difference in the anterior chamber angle structures between the positive and negative DRPT groups were compared. Based on the results of the DRPT, positive eyes of unilateral positive individuals were enrolled, and for the subjects with consistent DRPT results in bilateral eyes, the right eyes were chosen for data analysis. Main Outcome Measures IOP, the number of positional angle closures (NPAC), three subtypes of NPAC including NPAC-L,NPAC-B, NPAC-S. Results Out of the total of 70 subjects, 26 (37%) cases belonged to the positive group. Light-NPAC-S (r=0.260, P=0.030), dark-NPAC (r=0.249, P=0.038), dark-NPAC-B (r=0.306, P=0.010), and the change of NPAC-B (r=0.309, P=0.009) were found to be positively associated with IOP elevation during DRPT, while dark-TIA (r=-0.241, P=0.044) was found to exhibit a negative correlation. Only the change of NPAC-B (z=-2.64, P=0.008) was found to have a statistically significant difference between eyes with positive and negative outcomes. Conclusion Categorizing positional angle closure provides a more precise representation of angle conditions. S-type closure under well-lit conditions and B-type closure under dark conditions are believed to be associated with IOP elevation during DRPT. (Ophthalmol CHN, 2024, 33: 267-274)

Key words: ultrasound biomicroscopy, primary angle closure, biometry, anterior eye segment