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Objective: To evaluate changes in the speed of pupil constriction and in anterior segment parameters after laser peripheral iridotomy (LPI) in patients with angle closure using anterior segment optical coherence tomography., Methods: In this prospective observational study, videos of pupil and anterior segment changes in response to illumination were captured with real-time video recording using anterior segment optical coherence tomography and were analyzed frame by frame before and after LPI. Customized software was used to measure the speed of pupil constriction and changes in anterior chamber depth and anterior chamber area, as well as iris thickness at 750 μm from the scleral spur, at the sphincter muscle region (0.75 mm from the pupillary margin), and at the mid-iris location (half the distance between the scleral spur and the pupillary margin). Pupil diameter, angle opening distance, and trabecular-iris space area at 500 μm from the scleral spur were determined. The speed of pupil constriction was defined as the rate of pupil diameter change in response to illumination., Results: Twenty-nine patients were included. Most were Chinese (26 of 29 [90%]) and female (18 of 29 [62%]). The anterior chamber area, angle opening distance at 500 μm from the scleral spur, and trabecular-iris space area at 500 μm from the scleral spur were significantly higher after LPI (P < .001). A significant increase was observed in the speed of pupil constriction after LPI (P < .005). In response to illumination, the rate of change in iris thickness at the sphincter muscle region and at 750 μm from the scleral spur was faster after LPI (P < .05). Similarly, an increase was observed in the speed of change of angle-opening distance at 500 μm from the scleral spur in response to illumination after LPI (P < .05)., Conclusions: In patients with angle closure, changes in dynamic iridopupillary behavior are observed after LPI. The speed of pupillary constriction is faster after LPI.