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Editors Selection IGR 21-1

Surgical Treatment: Iridotomy for Angle-Closure Prevention: 14-year outcomes

Comment by Alanna James & Benjamin Xu on:

108334 Fourteen-Year Outcome of Angle-Closure Prevention with Laser Iridotomy in the Zhongshan Angle-Closure Prevention Study: Extended Follow-up of a Randomized Controlled Trial, Yuan Y; Wang W; Xiong R et al., Ophthalmology, 2023; 130: 786-794

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This study is a follow-up to the original six-year Zhongshan Angle-Closure Prevention (ZAP) trial and presents 14-year data on progression rates from primary angle-closure suspects (PACS) to primary angle closure (PAC). The ZAP trial, conducted in Guangzhou, China, enrolled 889 participants with bilateral PACS, defined as two or more quadrants of non-visible trabecular meshwork on gonioscopy without peripheral anterior synechiae (PAS) or elevated intraocular pressure (IOP) over 21 mmHg. One eye was randomized to treatment with laser peripheral iridotomy (LPI) and the other eye served as a control. The primary outcome measure was progression to PAC, defined as IOP greater than or equal to 24 mmHg, formation of one or more clock hours of PAS, or an episode of acute primary angle closure (APAC).

The six-year and 14-year ZAP trial findings are largely consistent with a few key differences. The 14-year data was completed in 499 of the treatment eyes (56.13%) and 501 of the control eyes (56.36%). The 14-year progression risk was three-fold lower among treated than control eyes, which is greater than the two-fold risk reduction reported in the six-year study. In both studies, the lower progression was lower largely due to lower risk of PAS formation in the treated group. The 14-year progression risk among control eyes remained low (1.4% per eye year), although this was higher than the six-year progression risk (0.8% per eye year). There were no new episodes of APAC between years six and 14 with total of five control eyes and one treated eye (p = 0.1). The 14-year number needed to treat to prevent one case of PAC was 12.4 compared to 44 at six years. Only two (0.22%) treated and four (0.45%) control eyes developed primary angle-closure glaucoma (PACG). The 14-year study found that patients with baseline IOP greater than 15 mmHg, Van Herrick grading less than 15%, and IOP increase after DRPPT less than 4 mmHg were two to three times more likely to progress to PAC. The authors again recommended against widespread LPI for PACS given these findings.

The 14-year number needed to treat to prevent one case of PAC was 12.4 compared to 44 at 6 years

The ZAP trial is a well-designed and executed study. By using fellow eyes as controls, confounding and biasing effects were mitigated. The 14-year sample size was robust despite participant attrition, providing sufficient statistical power to draw meaningful conclusions about long-term risk of progression. While the data shows LPI reduces risk of progression to PAC, this is primarily due to lower risk of PAS formation, which is of questionable clinical significance. One of the common critiques of the ZAP trial is its potential lack of generalizability due to a relatively homogeneous study population. Nevertheless, this study offers valuable information and provides compelling evidence to shift practice patterns away from widespread LPI treatment of PACS eyes. This approach helps reduce healthcare costs and avoid unnecessary complications in the form of inflammation, IOP spikes, dysphotopsias, and cataract formation. However, it is crucial to remember that a subset of PACS will eventually progress to PAC and PACG without treatment, which can be visually devastating. Therefore, additional clinical methods are needed to identify highrisk PACS patients who would benefit from LPI or other interventions.

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