The aim of this study was to evaluate laser peripheral iridotomy (LPI) induced changes in anterior segment parameters, using the anterior segment optical coherence tomography (ASOCT). Seventy-two subjects of Japanese ethnicity with primary angle closure suspect (PACS), primary angle closure (PAC) and primary angle closure glaucoma (PACG) were included. All participants underwent LPI and had ASOCT performed prior to and one month post LPI. Parameters assessed included angle opening distance, trabecular iris space area, anterior chamber depth, width, area and volume (iris thickness, curvature, area and lens vault). Complete data on 51 subjects was available for final analysis. There was a statistically significant increase in the angle width parameters (angle opening distance, trabecular iris space area and angle recess area) post LPI. The anterior chamber area, anterior chamber volume and anterior chamber depth increased significantly, and iris curvature was significantly reduced. There were no significant changes in anterior chamber width, lens vault, iris thickness and area. The mean gonioscopic angle width increased following LPI. The authors conclude that an increase in anterior chamber dimensions, angle widening and decrease in iris curvature; with a constant lens vault, iris thickness and iris area after LPI was seen in Japanese eyes with angle closure. The findings are consistent with the understood mechanism of LPI in relieving pupillary block.