Predictors of Selective Laser Trabeculoplasty Efficacy Results from the Swedish Optimal SLT Multicenter Randomized Controlled Trial.

Abstract

Purpose: To investigate the impact of potential predictor variables on selective laser trabeculoplasty (SLT) efficacy in the Swedish Optimal SLT (OSLT) trial.

Design: Post hoc analysis of a multicenter, masked, randomized controlled trial.

Subjects: 512 eyes from 399 patients enrolled in the OSLT trial.

Methods: Patients were randomized to one of four SLT variants, differing in treatment extent (180° or 360°) and laser power (standard or high). Analyses were performed with linear mixed models (LMMs), which allowed optimal use of all the data and applied comprehensive adjustment to the results. A wide selection of potential predictors for SLT efficacy were first analyzed separately regarding their association with intraocular pressure reduction (IOPR). Predictors meeting a threshold of p<0.1 were then included in a multivariable candidate model, which was refined through manual stepwise backwards selection until only significant variables (p<0.05) remained. Thereafter, other variables of interest were evaluated in this model.

Main outcome measure: Mean IOPR 1-6 months after SLT.

Results: The 360/high protocol remained the most efficacious SLT variant after adjustment for predictors (coefficient estimate (CE) 360/high 2.0, 360/standard 0.9, and 180/high -0.1, with 180/standard as the reference; p<0.001). Higher baseline IOP was a positive predictor for both absolute IOPR (CE 0.35; p<0.001), and relative IOPR (CE 0.72; p<0.001). A larger IOPR from the prior SLT (CE 0.18; p=0.004), as well as IOPR in the contralateral eye (CE 0.57; p<0.001) were also highly significant positive predictors. Conversely, the present analyses suggest that SLT efficacy is diminished by pseudoexfoliations (CE -0.69; p=0.02), the number of prior SLTs (CE -0.54; p=0.004), and increased corneal thickness (CE -0.01; p<0.002). Consultants/specialists and residents achieved similar SLT results, but individual surgeon performance mattered (p=0.003) as well as if the surgeon used the dominant hand (CE 0.35; p=0.050). However, age, glaucoma medication, cataract surgery, anterior chamber angle pigmentation, inflammatory symptoms, or postoperative anterior chamber flare had no correlation with SLT efficacy.

Conclusions: The 360/high protocol remained the most effective and reliable technique after adjustment for multiple predictors. No evidence was found to advise against 360/high SLT for any particular group of patients. Selective laser trabeculoplasty (SLT) is a first line treatment for open angle glaucoma and ocular hypertension (OHT).^1-3 SLT can be performed with different techniques (treatment protocols), primarily differing in the extent of the treatment area, the number of laser spots, and the principles for setting the laser power.⁴ For years, there has been a lack of evidence for the optimal treatment technique. Therefore, we designed the Optimal SLT (OSLT) trial, which is a large randomized controlled multicenter trial performed in Sweden. The study included 513 eyes from 400 patients randomized to one of four alternative SLT protocols differing in treatment extent (180 or 360 degrees), and laser power (standard or high). The study participants constitute one of the largest prospective SLT cohorts in the world. The OSLT methodology and primary results have been reported previously.⁴ The 360/high SLT protocol demonstrated a larger intraocular pressure (IOP) reduction (IOPR), a superior success rate, and a longer duration of effect, without reducing safety.