Investigators conducted a systematic literature review to evaluate the current findings about the optimal energy dose for IOP reduction via selective laser trabeculoplasty (SLT), particularly as it relates to patterns of application, trabecular meshwork (TM) pigmentation, and patient race/ethnicity.
Study design
The 44 reviewed articles included prospective, cross-sectional, and retrospective studies of the IOP-lowering effect of SLT. Articles were grouped into 4 categories: SLT dose-response alone, SLT response and level of TM pigmentation, SLT response in specific races and ethnicities, and SLT response in different laser application patterns.
Outcomes
Of the 17 studies investigating the effect of SLT energy dose and IOP reduction, only two found that higher total energy resulted in greater IOP reduction; in one, the high-energy SLT group also had higher pre-treatment IOP, a confounding factor since higher pre-treatment IOP is a known predictor of SLT success. Another study found that higher energy resulted in longer duration of success after SLT. All other studies found that SLT energy dose was not predictive of success. Trabecular meshwork pigmentation was also not found to be predictive of SLT efficacy in the articles that were analyzed. There were no meaningful conclusions regarding race and ethnicity as predictors of SLT success, as sample sizes were small within racial and ethnic subgroups; however, one article did find significantly higher success rates in patients of African descent than in patients of Indian or European descent. Regarding laser pattern application, higher energy application was not associated with greater SLT success, but there was a trend toward more complete TM coverage with non-overlapping spots predicting greater SLT success.
Limitations
More than half of the eyes originally examined were excluded for comorbid pathology or poor image quality. The reproducibility of OCTA images is highly sensitive to media opacities, and different imaging platforms can produce images with significantly different vessel densities. Changes over time could not be evaluated due to the cross-sectional nature of this study. Variations in definitions of success, energy settings, sample sizes, and length of follow-up pose a challenge when comparing studies. The authors did not comment on SLT response in primary open-angle glaucoma vs other secondary open-angle glaucomas (pigmentary, pseudoexfoliation, steroid response, for example), which would have seemed appropriate to investigate in this review. Predictors of SLT complications such as IOP spike, corneal edema, and iritis also were not included in this study.
Clinical significance
This article demonstrates that patients of all TM pigmentation levels and races stand to benefit from SLT, and that lower total energy levels are likely just as effective as higher energy levels in reducing IOP.