To assess anterior segment optical coherence tomographic measurements of patients after acute unilateral primary angle closure (APAC) compared with those of normal subjects. The clinical observational study included 41 hospital-based patients after unilateral APAC, their unaffected contralateral eyes, and 205 subjects. These were selected from the population-based Beijing Eye Study, and were matched with the APAC group for age, gender, and refractive error. All study participants underwent slit-lamp adapted optical coherence tomography (OCT). Compared with the unaffected contralateral eyes, eyes with APAC had a significantly shallower anterior chamber (P < 0.001), smaller chamber angle (P < 0.001), shorter anterior chamber opening distance (P < 0.01), a more marked iris root curvature (P < 0.05), and a greater number of quadrants that were closed (P < 0.001). Compared with the control group, eyes with APAC and the unaffected contralateral eyes both showed more shallow anterior chambers (P < 0.001), smaller chamber angles (P < 0.001), shorter chamber opening distances in each quadrant (P < 0.001), and a greater number of quadrants that were closed (P < 0.001). The angle was most often closed in the nasal quadrant. In the APAC group, the anterior chamber angle was closed in three or more quadrants. Anterior segment OCT measurements show significant differences between eyes with APAC, contralateral eyes at risk for APAC, and normal eyes. This may open possibilities for a semi-automatic assessment of subjects at risk for APAC by anterior segment OCT. The anterior chamber angle was closed most often in the nasal quadrant, and, in APAC, the angle was closed in three or more quadrants.