Mechanism of Action of Selective Laser Trabeculoplasty and Predictors of Response

Abstract

PurposeThis study was designed to evaluate the changes in aqueous humor dynamics (AHD) produced by selective laser trabeculoplasty (SLT) and to explore if baseline AHD parameters are predictive of IOP response to SLT.MethodsThirty-one consecutive subjects diagnosed with ocular hypertension or primary open-angle glaucoma scheduled to undergo SLT as their primary IOP-lowering therapy were enrolled in this prospective observational study. Subjects underwent baseline assessment of AHD in both eyes. Variables assessed were IOPs at 9 AM and noon, aqueous humor flow rate (fluorophotometry), episcleral venous pressure (EVP, venomanometry), outflow facility (pneumatonography and fluorophotometry) and uveoscleral outflow (calculated using modified Goldmann equation). All subjects underwent 360 degrees SLT and AHD measurements were repeated 3 months later.ResultsCompared with baseline, IOPs after SLT were significantly lower at 9 AM (22.9 ± 5.1 vs. 19.7 ± 3.0 mm Hg; P = 0.001) and noon (23.4 ± 4.6 vs. 20.0 ± 3.5 mm Hg; P < 0.001). Outflow facility by fluorophotometry was significantly increased from 0.17 ± 0.11 μL/min/mm Hg at baseline to 0.24 ± 0.14 μL/min/mm Hg at 3 months (P = 0.008). Outflow facility by tonography (baseline: 0.16 ± 0.07 μL/min/mm Hg vs. 3 months: 0.22 ± 0.16 μL/min/mm Hg; P = 0.046) was similarly increased. No change in aqueous flow or EVP was observed. There were no changes in IOP or AHD in the contralateral untreated eye. Using multiple linear regression models, higher baseline aqueous flow, lower baseline outflow facility, and possibly lower uvescleral outflow were associated with more IOP lowering with SLT.ConclusionsThe IOP-lowering effect of SLT is mediated through an increase in outflow facility. There is no contralateral effect. Higher aqueous flow and lower outflow facility may be predictive of better response to SLT.

Laser Trabeculoplasty and Aqueous Dynamics

“…This observation is in concordance with the observation of trabecular cell division even in untreated areas after trabeculoplasty [27]. Fluorophotometric measures showed a 41.2% increase in outflow facility after SLT [65].…”

Predictors of selective laser trabeculoplasty success in open angle glaucoma or ocular hypertension: does baseline tonography have a predictive role?

“…In our previous publications, [10,11] we demonstrated that IOP reduction was not fully explained by the amount of outflow facility enhancement at 3 months post SLT. However, Gulati et al [12] reported that lower baseline aqueous outflow facility 1 (measured by fluorophotometry and pneumatonometry) is significantly associated with IOP 3-month post SLT.…”

“…Gulati et al [12] showed that calculated uveoscleral outflow, episcleral venous pressure and aqueous flow rate remained unchanged 3-month post SLT. They demonstrated that higher baseline aqueous flow rate, lower fluorophotometric/pneumatonometric outflow facility and lower uveoscleral outflow were associated with IOP lowering effect of SLT.…”

Rho Kinase Inhibitors as a Novel Treatment for Glaucoma and Ocular Hypertension

“…Laser trabeculoplasty reduces trabecular outflow resistance 40 and various surgical procedures involve bypassing, incising or removing the trabecular meshwork 41 . It is notable, however, that none of the medications currently available to reduce IOP address the underlying cause of the elevated IOP that is commonly associated with glaucoma, namely increased outflow resistance 4, 42 .…”