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Purpose: We previously identified three distinct subgroups of patients with primary angle closure glaucoma (PACG) based on anterior segment optical coherence tomography (ASOCT) imaging. Group 1 was characterized by a large iris area with deepest anterior chambers, group 2 by a large lens vault (LV) and shallow anterior chamber depth (ACD), and group 3 displayed intermediate values across iris area, LV, and ACD. The purpose of the present study was to determine the distribution of plateau iris in these subgroups using ultrasound biomicroscopy (UBM) features., Methods: UBM images of the 210 subjects who were previously enrolled for the ASOCT subgrouping analysis and had undergone laser peripheral iridotomy were assessed and graded by a single glaucoma fellowship trained clinician. Plateau iris was defined as the presence of all the following UBM criteria in at least two quadrants: anteriorly directed ciliary body, absent ciliary sulcus, iris angulation, flat iris plane, and iridoangle touch., Results: Of 210 subjects, 23 were excluded due to poor-quality images. Based on standardized UBM criteria, the overall prevalence of plateau iris was 36.9% (n = 187). The proportion of plateau iris was similar across the three groups (subgroup 1:35.4% (n = 29); subgroup 2:39.0% (n = 32); subgroup 3:34.8% (n = 8), P = 0.87). On multiple logistic regression analysis, iris thickness at 750 μm from the scleral spur (IT750) was the only variable associated with plateau iris (odds ratio: 1.5/100 μm increase in iris thickness [IT], P = 0.04)., Conclusions: The proportion of plateau iris was similar across the three ASOCT-based PACG subgroups and more than one-third of subjects with PACG were diagnosed with plateau iris based on standardized UBM criteria. In addition, we noted that eyes with increased peripheral IT have an increased likelihood of plateau iris.