Two-Year Outcome of Selective Laser Trabeculoplasty for Normal-Tension Glaucoma in Japan: First-Line or Second-Line Selective Laser Trabeculoplasty (FSS) Study

<b>Objectives</b>: The objective of this study is to investigate the two-year continuous efficacy, risk factors, and safety profile of selective laser trabeculoplasty (SLT) in Japanese individuals diagnosed with normal-tension glaucoma (NTG) who underwent SLT as either a first-line or second-line treatment. <b>Methods</b>: A retrospective chart review was conducted of patients with NTG who underwent SLT as either an initial or secondary therapy at 26 medical institutions in Japan between January 2020 and December 2021 with a 2-year follow-up. The primary endpoint was a reduction in the rate of intraocular pressure (IOP) over 2 years after SLT. To estimate the time-varying effect of IOP reduction, a linear mixed-effects model was employed. The secondary endpoints were numerical IOP reduction, treatment success rates shown by a Kaplan-Meier analysis, and complications. Success was defined as an outflow pressure improvement rate (ΔOP) ≥ 20% (definition A) or an IOP reduction rate ≥ 20% (definition B) without further treatment. A Cox proportional hazards regression analysis was used to identify the risk factors to successful SLT treatment. The study was registered with UMIN-CTR (ID: UMIN R000064045). <b>Results</b>: A total of 230 eyes from 230 individuals participated in this study, with 148 eyes receiving SLT as an initial (first-line) therapy and 82 eyes undergoing SLT as a secondary (second-line) intervention. In the first-line group, the mean IOP dropped from 16.7 ± 2.3 mmHg to 13.7 ± 2.4 mmHg at two years post-treatment, reflecting a 16.8% reduction. In the second-line group, the average IOP declined from 15.9 ± 2.5 mmHg to 13.2 ± 2.0 mmHg, marking a 14.4% decrease over the same period. The treatment success rate according to definition A (ΔOP ≥ 20%) was 73.7% at 2 years. Analysis using a linear mixed-effects model identified time (<i>p</i> < 0.001), age (<i>p</i> = 0.044), baseline IOP (<i>p</i> < 0.001), and central corneal thickness (CCT) (<i>p</i> < 0.001) as statistically significant contributors to IOP reduction following SLT. However, neither the Group (first-line vs. second-line) variable (<i>p</i> = 0.386) nor the Time × Group interaction (<i>p</i> = 0.298) reached statistical significance. A lower baseline IOP and a thicker CCT were confirmed as significant predictors of SLT treatment failure. <b>Conclusions</b>: Both initial and secondary SLT treatments for NTG proved to be effective and safe over a two-year period, although the extent of IOP reduction was smaller in cases with a lower baseline IOP. Our findings indicate that the IOP-lowering effect of SLT in NTG is influenced by pretreatment IOP levels, aligning with previous studies on primary open-angle glaucoma and ocular hypertension. However, in contrast to those earlier findings, our research identified pretreatment central corneal thickness as a statistically significant factor influencing SLT efficacy in NTG. These results support the role of SLT as a reliable and safe therapeutic option for managing NTG.