Effect of laser peripheral iridotomy location on angle widening in primary angle closure suspects: the six-year ZAP trial

Background/aims To evaluate whether laser peripheral iridotomy (LPI) within the narrowest angle quadrant is associated with greater post-LPI angle widening in primary angle closure suspect (PACS) eyes. Methods Post hoc cohort analysis of the Zhongshan Angle-Closure Prevention Trial. Eyes assigned to LPI with baseline and 2-week anterior segment optical coherence tomography were included. Mean angle opening distance (AOD) measured 750 µm from the scleral spur (AOD750) was averaged across quadrants. Linear regression evaluated associations between LPI location (superior, temporal and nasal), LPI within the narrowest quadrant and change in mean AOD750 (∆AOD750). Logistic regression identified predictors of poor angle widening, defined as the lowest quintile of ∆AOD750. Data were censored if participants received cataract surgery during the 72-month follow-up. Results Among 427 PACS eyes, 208 underwent superior LPI, 175 underwent temporal LPI and 44 underwent nasal LPI. Superior LPI produced greater mean angle widening than temporal or nasal LPI (0.083, 0.073 and 0.063 mm, respectively). On univariable analysis, ∆AOD750 was associated with LPI location (p=0.04) but not with treatment within the narrowest quadrant (p=0.67). In multivariable linear regression, nasal LPI was associated with less widening than superior LPI (β=−22.36 µm; p=0.009), and no interaction was seen between LPI location and narrowest quadrant. In multivariable logistic regression, temporal LPI (OR 2.09 (95% CI 1.22 to 3.62), p=0.008) and nasal LPI (OR 3.32 (95% CI 1.49 to 7.24),p=0.004) temporal (OR 2.09; p=0.008) and nasal LPI (OR 3.32; p=0.004) were associated with higher odds of poor angle widening versus superior. Conclusions Superior LPI was associated with greater angle widening compared with temporal or nasal LPI locations regardless of whether the superior quadrant was the narrowest. Targeting the narrowest sector did not confer an anatomic advantage in PACS eyes.