Chang and colleagues have conducted a retrospective database study, drawn from the American Academy of Ophthalmology's Intelligent Research in Sight (IRIS) registry, of more than 260,000 eyes that underwent selective laser trabeculoplasty (SLT) to identify factors that predicted successful intraocular pressure (IOP) reduction following the procedure. Defining successful SLT as a > 20% reduction in IOP 8 weeks after the procedure, they reported an overall success rate of 37% and a success rate of 67% in eyes with pre-treatment IOP > 24 mmHg. As these findings suggest, higher baseline IOP was associated with a greater likelihood of successful SLT. Angle recession, uveitis, and aphakia increased the likelihood of unsuccessful SLT. The overall success rate of 37% is inconsistent with the preponderance of the SLT literature and significantly lower than that found in the recent Laser in Glaucoma and Ocular Hypertension Trial (LiGHT). However, the mean pre-treatment IOP was 19 mmHg and the mean number of medications per eye was 2.1, suggesting that many of these eyes underwent SLT with the goal of medication reduction rather than IOP reduction. These eyes would thus NOT be expected to manifest a ≥ 20% IOP reduction - success in these eyes would be unchanged IOP on fewer medications. Indeed, the investigators reported that among non-responders using one or more medications at baseline, 76.3% of eyes required fewer medications postoperatively--these would all be considered clinical successes.
The overall success rate of 37% is inconsistent with the preponderance of the SLT literature and significantly lower than that found in the recent Laser in Glaucoma and Ocular Hypertension Trial (LiGHT)
This is a significant limitation of registry studies and plagues both the SLT and the minimally invasive glaucoma surgery (MIGS) literature: these procedures have two distinct indications - IOP reduction or medication reduction - and the specific indication for each procedure is typically not recorded in such a way that the cohorts can be analyzed separately.
Consequently, the mean IOP reduction of the study sample is diluted by those seeking medication reduction and vice versa. This results in large ranges of IOP and medication reductions between studies, resulting from differences in the proportions of eyes seeking each outcome, that severely limit cross-study comparisons. The WGA has developed and promulgated a consensus document describing optimal endpoints for glaucoma surgical trials. It would be advantageous to explicitly include a recommendation that the eye-specific surgical goals (IOP reduction versus medication reduction) be specified a priori and studies be adequately powered and cohorts analyzed separately by goal to more robustly characterize eye-specific outcomes.