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 > or =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) mm2 (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 > or =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.