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Editors Selection IGR 23-4

Forms of Glaucoma: Prevention of PACG

Comment by Benjamin Xu on:

80641 Laser peripheral iridotomy for the prevention of angle closure: a single-centre, randomised controlled trial, He M; Jiang Y; Huang S et al., Lancet, 2019; 393: 1609-1618

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Primary angle-closure glaucoma (PACG), the most severe stage of primary angle-closure disease (PACD), is a common cause of permanent vision loss worldwide.¹ Primary angle-closure suspect (PACS), the earliest stage of PACD, is defined as angle closure detected on gonioscopy in two or more quadrants of the anterior chamber angle.² Progression from PACS to primary angle closure (PAC) occurs when patients develop peripheral anterior synechiae (PAS) or elevated intraocular pressure (IOP) greater than 21 mmHg. Patients with PAC and PACG benefit from treatment with laser peripheral iridotomy (LPI), which can alleviate angle closure and lower IOP.³ However, prior to the landmark Zhongshan Angle Closure Prevention (ZAP) trial by He and colleagues, the benefit of treating PACS eyes with LPI was unclear.⁴

Prior to the landmark Zhongshan Angle Closure Prevention (ZAP) trial, the benefit of treating PACS eyes with LPI was unclear

The ZAP trial was a randomized clinical trial that recruited 889 subjects with bilateral PACS through community-based screening in Guangzhou, China. One eye per subject was randomized to treatment with LPI and the other to observation. This elegant design allowed each subject to act as his/her own control. Subjects were followed for six years, with the primary outcome being progression from PACS to PAC. While the treatment group had a significantly lower rate of progression compared to the observation group (hazard ratio = 0.53, p = 0.004), the risk of progression was low in both groups: 0.80% per year in the treatment group and 0.42% per year in the observation group. Based on their cost effectiveness analysis, the authors estimated that 44 and 126 LPI would need to be performed to prevent one case of PAC and PACG, respectively.

Authors estimated that 44 and 126 LPI would need to be performed to prevent one case of PAC and PACG, respectively

While the ZAP trial provides valuable insight into the limited benefit of treating eyes with PACS based on its current definition, it is important not to over-generalize its results. The ZAP trial only studied Chinese subjects between the ages of 50 to 70. Therefore, it is unclear if an older or multi-ethnic cohort would display similar rates of progression. The ZAP trial also highlights the need for new clinical methods to help clinicians identify PACS patients with higher risk of progressing to PAC and PACG who would benefit from LPI treatment.

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