Residual anterior chamber angle closure in narrow-angle eyes following laser peripheral iridotomy: anterior segment optical coherence tomography quantitative study

To study quantitative changes in anterior chamber angle (ACA) after laser peripheral iridotomy (LPI) in narrow-angle eyes using anterior segment optical coherence tomography (AS-OCT). Eighteen subjects with narrow angles were imaged with AS-OCT for determining test-retest variability. Forty-six participants with narrow angles were scanned with AS-OCT before LPI and 4 weeks after LPI. The presence of ACA closure by both AS-OCT imaging and gonioscopy was compared before and after LPI. Three ACA parameters by AS-OCT, angle opening distance at 500 mu m (AOD(500)), trabecular-ris space area at 500 mu m (TISA(500)) and angle recess area at 500 mu m (ARA(500)), at both nasal and temporal quadrants were incorporated for analysis. The increment of ACA parameters defined as exceeding the 95% confidence interval of test-retest variability was assessed after LPI. All 3 parameters obtained from the 18 eyes showed good measurement reproducibility (intraclass correlation coefficient 0.850-0.979). Persistent angle closure was detected in 23.9% of eyes by gonioscopy, and in 34.8% of eyes by AS-OCT images at temporal quadrant after LPI. When assessed by measurement variability criteria, the percentage of eyes that showed no significant change in ACA parameters ranged from 23.9% to 45.7% after LPI. Overall, ACA parameters changed significantly after LPI; however, when assessed by AS-OCT, ACA remained unchanged in some narrow-angle eyes despite LPI. Our findings suggest that multiple causes other than pupillary block may contribute to narrow-angle closure following LPI.