PURPOSE: The aim of this study is to quantify changes in anterior segment morphology by the use of ultrasound biomicroscopy (UBM) after Nd:YAG laser iridotomy in primary angle closure (PAC) and PAC glaucoma (PACG) in European eyes. METHODS: A total of 35 eyes of 28 consecutive patients presenting with PAC or PACG were examined by UBM at presentation, and 1 week after Nd:YAG laser peripheral iridotomy (LPI). Mean age of patients was 63.5+/-14.4 (SD) years. Seventeen patients were females (60%). The trabecular-iris angle (TIA) was measured in the superior, nasal, inferior, and temporal quadrants. Baseline measurements were made under light and dark conditions. MAIN OUTCOME MEASURE: UBM measurements of the trabecular-iris angle (TIA) and the angle opening distance (AOD). DESIGN: Consecutive observational case series. RESULTS: All measurements were made in four quadrants. Before LPI, mean superior TIA was 3.59+/-4.5 degrees (mean+/-SD), nasal TIA was 6.37+/-4.9 degrees , inferior TIA was 9.33+/-7.6 degrees , and temporal TIA was 8.65+/-7.3 degrees in light conditions. After LPI, these values increased, respectively, to 12.58+/-6.9 degrees (P<0.05), 15.40+/-6.8 degrees (P<0.05), 16.37+/-7.4 degrees (P<0.05), and 15.95+/-11.3 degrees (P<0.05), showing a significant widening of the angle in all four quadrants. Superior AOD increased from 0.060+/-0.07 to 0.107+/-0.07 mm (P=0.09). No serious LPI-related complications were encountered. CONCLUSIONS: Dimensions of the anterior chamber angle can be significantly influenced by Nd:YAG laser iridotomy in narrow angle European eyes. UBM examination is a viable tool for the quantitative evaluation of the anterior chamber angle before and after laser iridotomy.