Laser peripheral iridotomy in eyes with narrow drainage angles: Ultrasound biomicroscopy outcomes. The Liwan eye study

Purpose: To assess the short-term effect of laser peripheral iridotomy (LPI) on anterior segment anatomy in angle-closure suspects using ultrasound biomicroscopy (UBM). Design: Prospective intervention study. Participants: Persons identified as angle-closure suspects aged 50-79 years from a population-based survey in Guangzhou, China. Intervention: Laser peripheral iridotomy was performed on 1 randomly selected eye. Ultrasound biomicroscopy examination was carried out before and 2 weeks after the intervention. Main Outcome Measures: Proportion of eyes with iridotrabecular contact (ITC), as well as changes in UBM parameters including angle opening distance (AOD), iris thickness (IT), iris curvature, iris ciliary process distance, trabecular-ciliary process distance (TCPD), and scleral spur to iris insertion distance (SS-IR). Results A total of 72 of 101 eligible subjects participated in the study. The proportion of people with UBM-identified ITC in >= 1 quadrant dropped from 95% (68/72) before to 59% (42/72) after LPI. After LPI, the mean AOD at 250 microns increased from 0.064 mm (standard deviation [SD], 0.052) to 0.085 (0.052) mm (P<0.001); angle recess area increased from 0.040 (0.030) to 0.070 (0.036) mm(2) (P<0.0001); TCPD increased from 0.537 to 0.561 mm (P = 0.001); IT at 750 microns increased from 0.440 to 0.459 mm (P = 0.094), and IT at 1000 microns increased from 0.471 to 0.488 mm (P = 0.0001). Eyes whose angles remained closed after LPI (pigmented trabecular meshwork not visible in >= 3 quadrants) tended to have shallower AOD both at 250 (0.071 vs. 0.049 mm; P = 0.09) and 500 microns (0.108 vs. 0.052 mm; P = 0.001), a thicker iris (IT at 750 microns, 0.447 vs. 0.415 mm; P = 0.041), a more anterior positioned ciliary body (TCPD, 0.514 vs. 0.562 mm; P = 0.03), and a statistically nonsignificant more anterior iris insertion (SS-IR: 0.085 vs. 0.125 mm; P = 0.061), before LPI. Conclusions: Laser peripheral iridotomy results in a significant increase in the angle width in Chinese people with narrow angles. However, some iridotrabecular contact was found in 59% of eyes with a patent iridotomy. This was associated with smaller anterior chamber angle dimensions and a thicker iris, both of which may play a causative role in maintaining angle closure after LPI.