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.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.UBM measurements of the trabecular-iris angle (TIA) and the angle opening distance (AOD).Consecutive observational case series.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.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.