Purpose: To assess the immediate effect of laser peripheral iridotomy (LPI) and mechanisms of angle closure in a population-based study of primary angle closure (PAC) suspects. Design: Prospective interventional study. Participants: People identified as PAC suspects aged 50 to 79 years from a population-based survey in Guangzhou, China. Intervention: Laser peripheral iridotomy was performed in 1 randomly selected eye. Examinations were carried out before and 2 weeks after the intervention. Main Outcome Measures: Intraocular pressure (IOP), ultrasound biometry, optical pachymetry, and gonioscopy. Results: A total of 72 people with bilateral suspected PAC participated in the study. Mean IOP decreased by 3 mmHg (P<0.001), but axial anterior chamber depth did not change significantly (P = 0.784) after LPI. Median limbal anterior chamber depth increased from 15% to 25% of peripheral corneal thickness (P<0.001, Wilcoxon signed-rank test). Median iridotrabecular angle width increased from 0° to 10° in the superior quadrant and from 10° to 30° in the inferior quadrant (P<0.001). Nevertheless, 14 eyes (19.4%) still had 3 or more quadrants in which the posterior (usually pigmented) trabecular meshwork could not be seen after laser iridotomy. Conclusions: This study confirms that LPI results in a significant increase in the angle width in Chinese people with narrow angles. However, one fifth of eyes had residual angle closure after LPI. Although this report confirms that iridotomy widens the anterior chamber angle in most PAC suspects, long-term prospective studies with a larger sample size are required to determine if the risks of PAC glaucoma and other related pathologic sequelae are reduced after prophylactic LPI and to investigate the risk-to-benefit ratio before recommending widespread use of prophylactic LPI in this population.
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