Quantitative Ultrasound Biomicroscopy Assessment of Anterior Chamber Angle Changes One Year After Laser Peripheral Iridotomy in Primary Angle Closure Suspects

Background: Laser peripheral iridotomy (LPI) is the first-line treatment for eyes with primary angle closure suspect (PACS), but the extent and durability of anterior chamber angle widening over time remain variable. Ultrasound biomicroscopy (UBM) allows detailed quantitative assessment of angle anatomy and underlying mechanisms of residual angle closure. Methods: In this prospective cohort study, 39 eyes of 20 PACS patients underwent UBM examination before LPI and at 1 month and 1 year post-procedure. Angle opening distance at 500 µm from the scleral spur (AOD500) and trabecular–ciliary process distance (TCPD) were measured in four quadrants under standardized light conditions. Paired comparisons and linear regression analyses were performed. Results: Mean AOD500 increased significantly from baseline (90.1 ± 52.5 µm) to 1 month (146.2 ± 58.2 µm, p < 0.001) and remained greater at 1 year (128.4 ± 48.8 µm, p < 0.001), with the largest changes observed in the superior quadrant. TCPD remained unchanged over time. Despite a patent iridotomy, iridotrabecular contact (ITC) persisted in 12.8% of eyes at 1 year. Plateau iris configuration was identified in 35.9% of eyes. Eyes with smaller baseline AOD500 showed a more limited anatomical response to LPI, although interaction testing did not reach statistical significance. Conclusions: LPI induces significant but partially attenuated anterior chamber angle widening at one year in PACS eyes. A substantial subset exhibits persistent angle closure, frequently associated with plateau iris configuration, underscoring the need for continued post-LPI anatomical surveillance and mechanism-based management.