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Editors Selection IGR 22-3

Laser Treatment: Laser Peripheral iridotomy in Narrow Angle suspects

Comment by Wei Wang & Minguang He on:

95997 The Singapore Asymptomatic Narrow Angles Laser Iridotomy Study: Five-Year Results of a Randomized Controlled Trial, Baskaran M; Kumar RS; Friedman DS et al., Ophthalmology, 2022; 129: 147-158

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Primary angle closure suspect (PACS) is very common, reaching 10% in the east Asian elder population. Whether we should perform prophylactic laser peripheral iridotomy among this massive number of people remained unclear until our ZAP trial was published in 2019. The ANA-LIS study that recently published by Baskaran and his colleagues from Singapore may provide additional important evidence to support the conclusions from the ZAP trial, which is that, despite the laser PI reducing the event rate by half, its benefit would likely to be small given the fact that the actual event rates were low in the control arm and majority of the events had no immediate threat to vision (primarily on PAS formation instead of acute attack or IOP elevation). Therefore, a widespread prophylactic treatment is not recommended.

The study designs of ZAP and ANA-LIS study are essentially very similar to each other in terms of the "split-body design", where one eye was randomly assigned to treatment and the fellow eye was treated as control. Both studies had long enough follow-up period of time (5-6 years) to observe the events of interest. The level of efforts on running such a long-term follow-up trial with high retention rates is tremendous. The event rates observed among the control arm appear to be different in ZAP (8 per 1000 eye-years) and ANA-LIS study (22 per 1000 eye-years). This could be in part explained by the difference in the definition of primary outcomes, such as: PAS was defined as one clock hour cumulatively in ZAP study and as half clock hour in ANA-LIS, also the IOP elevation was defined as 24 mmHg in ZAP and 21 mmHg in ANA-LIS.

The difference on the observed event rates, whether it is 8 per 1000 eye-years or 22 per 1000 eye-years, does not confer different messages to our clinical practice because the majority of these events were in fact on PAS formation, a very mild pathologic change that is unlikely to cause immediate vision threat. Interestingly, ANA-LIS study identified the event rates on IOP elevation > 21 mmHg or acute angle closure or PACG development were in fact not statistically significantly different among the treated and untreated eyes while the only difference was on PAS formation.

The event rates on acute attack were extremely low in both studies. This would suggest the risk of developing acute attack among people with PACS is in fact lower than what we expected initially before these two studies were published.

Both studies failed to identify or to fully confirm these "predictors" due to the low event rates

One of the initial purposes of these two studies is to identify risk factors that are associated with PAC or PACG development. However, both studies failed to identify or to fully confirm these "predictors" due to the low event rates. Further analysis on the anterior segment OCT imaging data might help identify some "anatomical" features that are associated with the conversion from PACS to PAC.

Finally, both studies confirm that the side effects of laser PI on the corneal endothelium and lens opacity were minimal. This is another finding that is in common from both studies that deserves our attention in clinical practice.

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