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Editors Selection IGR 9-4

Laser Treatment: Optimizing SLT Performance

Comment by Abdus Samad Ansari & Gus Gazzard on:

112722 Optimal Performance of Selective Laser Trabeculoplasty: Results from the Swedish Optimal SLT Multicenter Randomized Controlled Trial, Dahlgren T; Ayala M; Zetterberg M, Ophthalmology. Glaucoma, 2023; 0:

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Clinicians and researchers work hard to conduct trials that establish treatment efficacy and improve patient outcomes. The advent of Selective Laser Trabeculoplasty (SLT) as a firstline therapy has transformed glaucoma management.¹ This shift is based on high-quality evidence informing healthcare decisions at both population and individual levels. Despite the recognized utility of SLT therapy, there remains a considerable lack of evidence concerning its optimization. A Cochrane review in 2022 highlighted that comparative trials on SLT protocols have been underpowered and thus inconclusive in their conclusions.² Clinical equipoise exists for problems where investigators remain uncertain about a clinical question such as an intervention's effectiveness in treating a disease and require randomized trials. Dahlgren and colleagues question how SLT treatment protocols can be optimized. Current protocols used worldwide vary, with the most significant differences concerning the number of laser applications, and laser power settings.

In this clinical trial, the investigators aimed to evaluate the clinical outcomes of the four most established SLT protocol variants. In total, 400 patients with glaucoma or ocular hypertension, comprising both treatment-naive (30%) and those receiving ongoing therapy, were recruited. SLT was administered with either 50 ± 5 laser spots over 180 degrees or 100 ± 10 spots over 360 degrees. Laser power was calibrated to either just below the cavitation bubble threshold ('standard energy') or to a level producing cavitation bubbles ('high energy'), resulting in four distinct protocols: 180-standard, 180-high, 360-standard, and 360-high. The primary outcomes assessed included intraocular pressure (IOP) reduction one to six months post-SLT, the proportion of patients achieving a 20% IOP reduction, and the time to treatment escalation. The 360/high protocol demonstrated superiority across all primary endpoints, exhibiting greater IOP reduction (5.4 mmHg), higher success rates (58.3%), and a longer median time to treatment escalation (1323 days), all of which were found to be statistically significant in comparison to the other protocols at the time points studied. Postoperative discomfort was more frequent in this patient group, although mild and temporary, with adverse events being rare overall. The authors recommend the 360-high SLT protocol as the standard treatment because their results suggest superior efficacy and relative safety.

The authors conducted a well-structured and methodologically sound clinical trial, adequately powered to address common trial challenges such as attrition, recruitment, and randomization. Sensitivity and post-hoc subgroup analysis appeared to validate results even when stratifying eyes by subtype, including those with and without pseudoexfoliation, cataract surgery and treatment-naivety or those with prior glaucoma surgery. Efficacy, as expected, varied within these cohorts, with similar trends pointing to a 360-high protocol. A pivotal finding reported by the investigators is the survival analysis, i.e., time from SLT to treatment escalation. This significantly favored the 360-high SLT protocol and revealed a treatment effect that was more than twice as pronounced, supporting prior data from other studies supporting significant duration of effect for SLT.

A pivotal finding reported by the investigators is the survival analysis, i.e., time from SLT to treatment escalation. This significantly favored the 360-high SLT protocol and revealed a treatment effect that was more than twice as pronounced, supporting prior data from other studies supporting significant duration of effect for SLT

Treatment effectiveness can vary across different populations and patient characteristics. This does limit the trial's external validity, particularly relating to patients with subtypes of disease where SLT is still unexplored and protocols are yet to be defined, such as angle closure, pigmentary or normotensive disease. Regretfully, visual field data was not consistently gathered throughout the trial. This may have been a missed opportunity considering this mixed population of treated and treatment-naive patients, possibly deepening our knowledge of SLT and visual field progression and what has been established through the LiGHT trial.³ Despite this, the study has more to give us, and it will be interesting to see the long-term follow-up results beyond the six months currently reported.

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