Selection of Laser Peripheral Iridotomy Location Based on Localized Angle Narrowing: The Zhongshan Angle-Closure Prevention Study

Abstract

Purpose : Laser peripheral iridotomy (LPI) is a common treatment for primary angle closure glaucoma, a leading cause of permanent blindness. There is currently no consensus regarding optimal LPI location. In our previous study, superior LPI location was associated with greater angle widening, which may be protective against angle closure progression. Here, we investigate the etiology of this effect and whether LPI targeting the narrowest rather than the superior sector yields improved anatomical outcomes.

Methods : Participants of the Zhongshan Angle Closure Prevention Trial with bilateral primary angle closure suspect (PACS) status underwent anterior segment OCT imaging at baseline and 2 weeks after LPI. PACS was defined as the inability to visualize pigmented trabecular meshwork in ≥ 2 quadrants on gonioscopy. LPI was performed on 1 eye per patient in a superior, temporal, or nasal location. Logistic regression was used to assess the association between LPI location/s and poor angle widening, defined as the lowest quintile of change in mean angle opening distance measured at 750 mm from the scleral spur (AOD₇₅₀₎.

Results : 427 eyes with PACS were treated with LPI (superior LPI: 219, temporal LPI: 93, nasal LPI: 115). The increase in mean AOD₇₅₀ was statistically different in eyes treated in superior LPI compared to temporal LPI or nasal LPI (0.084 mm vs 0.076 vs 0.064; p=0.03). When the superior sector was most narrow, LPI within and outside the sector produced similar increases in mean AOD₇₅₀ at the 2-week visit (0.085 mm vs 0.077; p=0.27). Similar effects of LPI within and outside the sector persisted for temporal (0.056 mm vs 0.073 respectively; p=0.12) and nasal (0.064 mm vs 0.081, respectively; p=0.31) sectors. In multivariable analysis, nasal LPI (OR: 4.04; p<0.001) and temporal LPI (OR: 2.39; p=0.002) were associated with higher odds of poor angle widening (lowest 20% of AOD₇₅₀) relative to superior LPI after controlling for baseline AOD₇₅₀.

Conclusions : Superior LPI produces greater angle widening compared to temporal or nasal LPI locations regardless of which sector exhibits the greatest angle narrowing at baseline. Superior LPI location can be considered to optimize anatomic outcomes in PACS eyes as there does not appear to be a localized effect of treatment. The long-term clinical benefit of greater angle opening with superior LPI requires additional study.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.