Predictors of Short-Term Intraocular Pressure Change after Laser Peripheral Iridotomy: A Prospective Randomized Study

Purpose: To describe short-term intraocular pressure (IOP) changes after laser peripheral iridotomy (LPI) and identify factors predicting IOP lowering. Design: Multicenter, prospective randomized study. Participants: Four hundred fifty-five South Indian eyes of 455 participants 30 years of age or older with a diagnosis of primary angle-closure suspect (PACS), primary angle closure (PAC), or PAC glaucoma (PACG). Methods: Participants were randomized to superior or nasal/temporal LPI. Multivariate regression models were used to determine preoperative features and LPI parameters associated with change in IOP from baseline to the 2-week postoperative examination. Main Outcome Measures: Change in IOP at 2 weeks after LPI compared with baseline. Results: Among all treated eyes, 11.0% of eyes demonstrated a 20% or more decrease in IOP after LPI, whereas 19.6% demonstrated at least a 20% increase in IOP. Intraocular pressure changes occurring after LPI did not differ by LPI location (P > 0.5 for all comparisons). Although the anterior chamber angle widened after LPI (P < 0.001) and was classified as open after laser in most eyes (64% in all 4 quadrants), there was no significant association between gonioscopic angle opening and LPI-induced IOP change (P = 0.7). Linear regression analysis demonstrated more IOP lowering with higher baseline IOP (3.2 mmHg more lowering per 10-mmHg higher baseline IOP; 95% confidence interval [CI], 2.3–4.1 mmHg) and PAC/PACG diagnosis (1.4 mmHg more IOP lowering vs. PACS diagnosis; 95% CI, 0.2–2.6 mmHg) predicted a lower IOP after LPI. After multivariate adjustment, only higher baseline IOP predicted lower IOP after LPI (P < 0.001). Features not associated with IOP lowering included demographic, visual, and A-scan measures; baseline gonioscopic angle width; total laser energy; LPI area; and LPI location (P > 0.08 for all). Eyes with PAC/PACG, as compared with PACS, demonstrated more IOP lowering after LPI (1.2±1.7 mmHg vs. –0.4±1.0 mmHg; P < 0.001) after adjusting for baseline IOP. Conclusions: Neither LPI location nor degree of gonioscopic angle opening was associated with statistically significant change in IOP after LPI. Although significant IOP lowering after LPI was uncommon in the overall cohort, higher baseline IOP and PAC/PACG diagnosis predicted lower postoperative IOP.