Selective laser trabeculoplasty: Does energy dosage predict response?

Optimal Performance of Selective Laser Trabeculoplasty: Results from the Swedish Optimal SLT Multicenter Randomized Controlled Trial

PURPOSE

Selective laser trabeculoplasty (SLT) is a first-line treatment for glaucoma and ocular hypertension. However, due to insufficient comparative evidence in efficacy and safety, several SLT treatment protocols are currently used in practice. The objective of this trial was to compare the clinical outcomes of the 4 most significant SLT variants.

DESIGN

Prospective, multicenter, masked, randomized controlled trial (RCT).

PARTICIPANTS

Four hundred patients with glaucoma or ocular hypertension. The cohort consisted of both treatment-naive patients and patients undergoing glaucoma treatment, at different stages of disease.

METHODS

Selective laser trabeculoplasty was performed with 50 ± 5 laser spots in 180 degrees or with 100 ± 10 spots in 360 degrees. The laser power was titrated to either just below the cavitation bubble level ("standard energy") or to a level producing cavitation bubbles at 50% to 75% of laser applications ("high energy"). Thus, 4 different treatment protocols were included - 180/standard, 180/high, 360/standard, and 360/high. The study adhered as close as possible to regular clinical management, but within a scientific framework.

MAIN OUTCOME MEASURES

Reduction of intraocular pressure (IOP) 1 to 6 months after SLT. The proportion of patients achieving a 20% IOP reduction without any further intervention. Time to glaucoma treatment escalation in a Kaplan-Meier survival analysis.

RESULTS

SLT performed with the 360/high protocol was shown to be superior regarding all primary endpoints. The IOP reduction 1 to 6 months after SLT was 5.4 mmHg in the 360/high group, compared to 3.4, 3.2, and 4.2 mmHg with the 180/standard, 180/high, and 360/standard protocols, respectively (P < 0.001). Furthermore, the success rate after 6 months was significantly higher -58.3%, compared with 30.2%, 29.3%, and 41.7% (P < 0.001). The median time to glaucoma treatment escalation was more than twice as long with 360/high SLT -1323 days, compared to 437 days, 549 days, and 620 days (P < 0.001). Although postoperative discomfort was more frequent with the 360/high protocol, symptoms were generally mild and transient. Adverse events were rare in all groups.

CONCLUSIONS

The magnitude and longevity of SLT results increases substantially if SLT is performed according to the 360/high protocol, without compromising safety. Therefore, we recommend that 360/high SLT be considered as standard treatment.

FINANCIAL DISCLOSURES

The authors have no proprietary or commercial interest in any materials discussed in this article.

Fixed High Energy Versus Standard Titrated Energy Settings for Selective Laser Trabeculoplasty

PRCIS

Fixed high-energy selective laser trabeculoplasty (SLT) is associated with a greater reduction in intraocular pressure (IOP) compared with the standard titrated approach at up to 36 months postprocedure.

PURPOSE

There is no consensus on ideal SLT procedural laser energy settings. This study aims to compare fixed high-energy SLT to the standard titrated-energy approach within the setting of a residency training program.

PATIENTS

Patients over the age of 18 years received SLT between 2011 and 2017, a total of 354 eyes. Patients with a prior history of SLT were excluded.

METHODS

Retrospective review of clinical data from 354 eyes that underwent SLT. Eyes that underwent SLT using fixed high energy (1.2 mJ/spot) were compared with those with the standard titrated approach starting at 0.8 mJ/spot and titrating to "champagne" bubbles. The entirety of the angle was treated using a Lumenis laser set to the SLT setting (532 nm). No repeat treatments were included.

MAIN OUTCOME MEASURE

IOP and glaucoma medications.

RESULTS

In our residency training program, fixed high-energy SLT was associated with a reduction in IOP compared with a baseline of -4.65 (±4.49, n = 120), -3.79 (±4.49, n = 109), and -4.40 (±5.01, n =119) while standard titrated-energy was associated with IOP reduction of -2.07 (±5.06, n = 133), -2.67 (±5.28, n = 107), and -1.88 (±4.96, n = 115) at each respective postprocedural time point (12, 24, and 36 months). The fixed high-energy SLT group had significantly greater IOP reduction at 12 months and 36 months. The same comparison was performed for medication naïve individuals. For these individuals, fixed high-energy SLT resulted in IOP reductions of -6.88 (±3.72, n = 47), -6.01 (±3.80, n = 41), and -6.52 (±4.10, n = 46) while standard titrated-energy had IOP reductions of -3.82 (±4.51, n = 25), -1.85 (±4.88, n = 20), and -0.65 (±4.64, n = 27). For medication naïve individuals, fixed high-energy SLT resulted in a significantly greater reduction in IOP at each respective time point. Complication rates (IOP spike, iritis, and macular edema) were similar between the two groups. The study is limited by overall poor response to standard-energy treatments, whereas high-energy treatments showed similar efficacy to those in literature.

CONCLUSION

This study demonstrates that fixed-energy SLT produces at least equivalent results compared with the standard-energy approach, without an increase in adverse outcomes. Particularly in the medication naïve subpopulation, fixed-energy SLT was associated with a significantly greater IOP reduction at each respective time point. The study is limited by overall poor response to standard-energy treatments, with our results showing decreased IOP reduction compared with those of previous studies. These poor outcomes of the standard SLT group may be responsible for our conclusion that fixed high-energy SLT results in a greater reduction in IOP. These results may be useful when considering optimal SLT procedural energy in future studies for validation.

Energy Dose-Response in Selective Laser Trabeculoplasty: A Review

PRCIS

A literature review of selective laser trabeculoplasty (SLT) energy dose-response found no definitive relationship between intraocular pressure (IOP) reduction with respect to total or pulse energy, race, pigmentation, or application pattern.

PURPOSE

SLT is a safe and effective treatment for lowering IOP. Although evidence is mounting for the advantage of its use as a first-line treatment for IOP reduction, the SLT procedures in use vary widely. The purpose of this literature review was to investigate whether there were any relationships between SLT energy and efficacy for lowering IOP in the published literature.

METHODS

A literature review was undertaken that included studies in which energy levels required for successful SLT treatment were investigated: in general, with respect to angle pigmentation, race or ethnicity, and treatment arc extent.

RESULTS

There was no indication that higher (or lower) energy used in the treatment leads to greater (or less) IOP reduction. Similar results were obtained regarding the level of trabecular meshwork pigmentation. Race was not found to be associated with altered dose response in SLT. There were indications that treating the full 360 degrees, as opposed to smaller arcs, could be beneficial for more IOP reduction. IOP reduction from SLT was found to be similar to that provided by topical medications.

CONCLUSIONS

The optimal energy level of SLT needed for IOP reduction has not yet been definitively established, with all reported pulse energies resulting in similar IOP reduction. Furthermore, similar lack of conclusive findings exists regarding optimal SLT energy dosage for use in different races and degrees of trabecular meshwork pigmentation. This parameter and each of the abovementioned factors requires further research.

Laser Induced Damage to Disposable Gonioscopy Lenses During Selective Laser Trabeculoplasty

The substitution of reusable gonioscopy lenses for disposable gonioscopy lenses during selective laser trabeculoplasty (SLT) has occurred over the last few years to mitigate infection risk. However, concerns have been raised regarding the potential of laser damage to the lens itself during SLT, which can lead to laser scattering, increasing the possibility of unintended adverse effects. We have noticed that over 90% of the disposable lenses used for SLT sustained some sort of laser-induced damage with routine laser energies (0.4-1.0 mJ). Comparisons of clinical efficacy of SLT, measured by reductions in intraocular pressure (IOP), between the use of reusable and disposable lenses has shown no difference in IOP reduction, with both groups achieving a 20% reduction in IOP over the course of 12 months. While no clinical difference in outcomes was observed, further investigation into this issue, most notably the possibility of adverse effects due to laser scattering, is warranted.

Selective laser trabeculoplasty: A review

Glaucoma is the second most prevalent cause of blindness worldwide, and the only effective management is the lowering of intraocular pressure (IOP). Selective laser trabeculoplasty (SLT) has become an essential part of glaucoma management since its commercial release in 2001. It has been an improvement from the previous argon laser trabeculoplasty (ALT), by using 1% of the laser energy, reducing the amount of anterior segment inflammation and minimising the degree of mechanical injury to the trabecular meshwork. There is now a large volume of work that demonstrates SLT is equally effective as ALT and topical medication in lowering IOP. It is simple to perform, with a well described side-effect profile, and is long-lasting and repeatable. This review will summarise the current literature on SLT for each of these topics.

Low-energy Selective Laser Trabeculoplasty Repeated Annually: Rationale for the COAST Trial

The recent Laser in Glaucoma and Ocular Hypertension Trial provided the evidentiary basis for a paradigm shift away from the historical medication-first approach to glaucoma--which has numerous limitations, the most important of which is poor adherence to therapy --and toward a laser-first approach. Now 20 years after its commercialization, selective laser trabeculoplasty (SLT) is routinely performed consistently with its initial description, with energy titrated to the appearance of fine, champagne-like cavitation bubbles. A recent data set suggested that lower energy SLT, applied as primary therapy and repeated annually irrespective of intraocular pressure--rather than pro re nata when its effect wanes and irrespective of intraocular pressure rises --yields longer medication-free survival than standard energy SLT repeated pro re nata. A new study--Clarifying the Optimal Application of SLT Therapy --has been initiated to explore this preliminary finding in a pair of consecutive randomized trials. Herein, we provide an evidence-based rationale for the use of low-energy SLT repeated annually as primary therapy for mild to moderate primary open-angle glaucoma or high-risk ocular hypertension.

Selective Laser Trabeculoplasty: Outcomes of Multiple Repeat Treatments

PURPOSE

To characterize intraocular pressure (IOP) reduction, effect duration, and side effect profile of repeat selective laser trabeculoplasty (SLT) used as primary stand-alone treatment for open-angle glaucoma (OAG). The secondary aim was to investigate covariates associated with treatment response to SLT.

DESIGN

Retrospective chart review.

PARTICIPANTS

A total of 52 patients with treatment-naïve OAG who received 3 installments of 360⁰ SLT as stand-alone glaucoma therapy. When both eyes met the inclusion criteria, only right eye data were used for analysis.

METHODS

The study was conducted in a single specialist practice. First, second, and third SLT (SLT1, SLT2, SLT3, respectively) treatments were compared for IOP reduction and effect duration. Eyes were classified as "treatment responders" if they had ≥20% IOP reduction 4 to 8 weeks post-SLT compared with baseline. Effect duration was the interval between SLT and the time point at which the surgeon decided inadequate IOP control necessitated repeat SLT. Individuals were excluded if they underwent intraocular surgery during the study period or received treatment with adjunctive ocular hypotensive medications.

MAIN OUTCOME MEASURES

Reduction in IOP post-SLT and effect duration between treatments.

RESULTS

Mean age at SLT1 was 58 years; 50% were male, and 92% were phakic. The SLT1 and SLT3 both resulted in mean 27% IOP reduction at 4 to 8 weeks, whereas SLT2 led to 26% IOP reduction. Response rate (≥20% IOP reduction at 4-8 weeks) was 79% for SLT1, 73% for SLT2, and 81% for SLT3, but the difference was not statistically significant. Response to repeat SLT was not significantly associated with previous SLT outcome. Effect duration was 22.2 months, 33.8 months, and 28.9 months after SLT1, SLT2, and SLT3, respectively. Effect duration was significantly longer after SLT2 (P = 0.0006) and SLT3 (P = 0.0444) compared with SLT1. There was no significant association between SLT response and gender, lens status, or OAG subtype.

CONCLUSIONS

For primary stand-alone treatment in OAG, initial and repeat SLTs produced comparable percentage IOP reduction, but repeat SLTs had longer effect duration. Intraocular pressure response to SLT was not predictive of the IOP response to subsequent, repeat SLT treatment.

Short-Term Efficacy of Selective Laser Trabeculoplasty in Omani Eyes with Glaucoma: A Single Institutional Study

Purpose

There is some evidence suggesting a different nature of response to selective laser trabeculoplasty (SLT) among different races. Therefore, we aimed to assess the short-term efficacy, safety and nature of outcome of SLT in Omani eyes.

Patients and Methods

A retrospective review was performed of patients with open-angle glaucoma (OAG) or ocular hypertension (OHTN) who underwent a single session of 360-degree SLT between January 1, 2017 and December 31, 2018. The main outcome was mean IOP reduction and attainment of treatment success at 5 weeks and 12 weeks post treatment defined as at least 20% IOP reduction from baseline without further medications or interventions. Secondary outcomes were frequency of adverse events and factors predicting success.

Results

A total of 33 eyes of 33 Omani patients who underwent treatment with SLT were analyzed. The nature of response to laser followed a gradual pattern as the mean IOP reduction from baseline was 20.2% (5.21 mm Hg, P <0.001) at 5 weeks and further enhanced to 27.2% (6.95 mm Hg, P <0.001) at 12 weeks. Short-term success was achieved in 51.5% and 72.2% of eyes at 5 and 12 weeks, respectively. SLT was most effective in OHTN subgroup and those with higher baseline IOP (both P <0.001). Side effects were an infrequent occurrence, minor and transient.

Conclusion

The short-term success of SLT in Omani eyes was clinically relevant and comparable to the gradual pattern seen in patients of Indian ancestry. It is a safe therapeutic option in selective Omani eyes.

SELECTIVE LASER TRABECULOPLASTY: MECHANISMS OF ACTION AND PREDICTORS OF EFFICACY

This review considered selective laser trabeculoplasty in comparison with other methods for therapeutic and surgical treatment of primary open-angle glaucoma and ocular hypertension, including argon laser trabeculoplasty. In this paper, we reviewed current knowledge on the mechanisms of action of selective laser trabeculoplasty, predictors of intraocular pressure-lowering effect, repeatability, and safety of this procedure.

West Indies Glaucoma Laser Study (WIGLS)-2: Predictors of Selective Laser Trabeculoplasty Efficacy in Afro-Caribbeans With Glaucoma

PURPOSE

To identify factors associated with intraocular pressure (IOP) reduction following selective laser trabeculoplasty (SLT) in Afro-Caribbean people with primary open-angle glaucoma (POAG).

DESIGN

This was a prospective stepped-wedge study.

METHODS

Data were drawn from 72 Afro-Caribbean subjects with POAG participating in the ongoing West Indies Glaucoma Laser Study. Multivariable mixed-model analysis was utilized to develop a predictive model for percent IOP reduction 12 months following SLT. Putative factors (age, sex, site, baseline IOP, prior use of prostaglandin therapy, number of prewashout IOP-lowering medications, central corneal thickness, severity of glaucoma, duration of follow-up, and signs of acute postoperative inflammation) were evaluated in bivariate analysis. Factors significant at P≤0.2 were included in the final model. Right and left eye data were modeled separately.

RESULTS

At month 12 following SLT, mean IOP reductions in the West Indies Glaucoma Laser Study were 6.2 to 6.5 mm Hg (29.7% to 31.0%) in right and left eyes. The only factor significant in both eyes (P=0.0005 in right eyes and P<0.0001 in left eyes) was time, with IOP reductions being greatest at month 3 and declining slightly over time through month 12. Vertical cup-disc ratio (P=0.006) and prior prostaglandin therapy (P=0.004) were significant only in right eyes, and central corneal thickness (P=0.014) was significant only in left eyes. Factors significant only unilaterally did not approach significance in fellow eyes, suggesting the possibility that these represent type 1 errors. Site (St. Lucia vs. Dominica) was not a significant factor, establishing generalizability of these treatment outcomes to a broader population of African-derived people.

CONCLUSIONS

This analysis did not identify any subject-specific factors consistently predictive of therapeutic response to SLT. Of note, no factors predicted a suboptimal response. These findings favorably position SLT for broad application as primary therapy in African-derived people with POAG.

Primary Selective Laser Trabeculoplasty for Open-Angle Glaucoma and Ocular Hypertension: Clinical Outcomes, Predictors of Success, and Safety from the Laser in Glaucoma and Ocular Hypertension Trial

PURPOSE

To report clinical efficacy, predictors of success, and safety of primary selective laser trabeculoplasty (SLT) used in treatment-naive patients with open-angle glaucoma (OAG) or ocular hypertension (OHT).

DESIGN

Post hoc analysis of a multicenter, prospective, randomized, controlled trial.

PARTICIPANTS

Treatment-naive patients with OAG or OHT.

METHODS

Patients randomized to SLT or topical medication and treated to predefined target intraocular pressures (IOPs) requiring ≥20% IOP reduction from baseline for all disease severity levels.

OUTCOME MEASURES

Initial (early) absolute IOP-lowering at 2 months. Achievement of drop-free disease-control: meeting target IOP without disease progression or need for additional topical medication over 36 months after SLT. Predictors of early absolute IOP-lowering and drop-free disease-control after single initial SLT. Frequency of laser-related complications.

RESULTS

A total of 611 eyes (195 OHT and 416 OAG) of 355 patients received SLT, and 622 eyes (185 OHT and 437 OAG) of 362 patients received topical medication at baseline. Early absolute IOP-lowering after SLT was no different between OHT and OAG eyes (adjusted mean difference = -0.05 mmHg; 95% confidence interval [CI], -0.6 to 0.5 mmHg; P = 0.85). No difference was noted in early absolute IOP-lowering between topical medication and primary SLT (adjusted mean difference = -0.1 mmHg; 95% CI, -0.6 to 0.4 mmHg; P = 0.67). Early absolute IOP-lowering with primary SLT was positively associated with baseline IOP (coefficient 0.58; 95% CI, 0.53-0.63; P < 0.001) and negatively with female gender (coefficient -0.63; 95% CI, -1.23 to -0.02; P = 0.04). At 36 months, 536 eyes (87.7% of 611 eyes) of 314 patients (88.5% of 355 patients) were available for analysis. Some 74.6% of eyes (400 eyes) treated with primary SLT achieved drop-free disease-control at 36 months; 58.2% (312 eyes) after single SLT. Total SLT power and 2-month IOP were predictors of drop-free disease-control at 36 months after single SLT. Six eyes of 6 patients experienced immediate post-laser IOP spike (>5 mmHg from pretreatment IOP) with 1 eye requiring treatment.

CONCLUSIONS

Primary SLT achieved comparable early absolute IOP-lowering in OHT versus OAG eyes. Drop-free disease-control was achieved in approximately 75% eyes at 36 months after 1 or 2 SLTs, the majority of these after single SLT. These analyses are exploratory but support primary SLT to be effective and safe in treatment-naive OAG and OHT eyes.

Intraocular Pressure-Lowering Potential of Subthreshold Selective Laser Trabeculoplasty in Patients with Primary Open-Angle Glaucoma

Purpose. To compare the efficacy of subthreshold and conventional selective laser trabeculoplasty (SLT) in lowering intraocular pressure (IOP) in the patients with primary open-angle glaucoma (POAG). Methods. Fifty-two eyes from fifty-two POAG patients were randomized into two groups, one group treated with subthreshold SLT using two-thirds of the conventional energy and the other one treated with the conventional energy. IOP was measured with the Goldmann tonometer and the anterior chamber inflammation was determined using laser flare meter. Results. The initial energy dosage used in subthreshold SLT group was significantly lower than the amount of the energy used in conventional SLT group (0.4 ± 0.1 mJ versus 0.6 ± 0.1 mJ, P = 0.030). The total energy dosage was also significantly lower in subthreshold SLT group compared to the other group (37.6 ± 3.3 mJ versus 51.8 ± 5.7 mJ, P = 0.036). However, the level of inflammation in aqueous humor, amount of reduction in IOP, and the success rate in controlling IOP was the same in both groups. Conclusion. The efficacy of subthreshold SLT group in reducing IOP in POAG patients is comparable to the efficacy of conventional SLT group.

Selective laser trabeculoplasty as a first-line therapy: a review

Poor adherence with glaucoma medications has been well documented. There remains a significant unmet need for a relatively safe intraocular pressure (IOP)-lowering procedure that minimizes or eliminates patient participation, and thus reduce the incidence of treatment failures attributable to nonadherence. Selective laser trabeculoplasty (SLT) offers several advantages: It effectively reduces IOP in most patients with open-angle glaucoma, it is cost-effective compared with eye drops, it can be repeated if needed, and it eliminates the issue of adherence to medications when used as an initial treatment. This article reviews the evidence supporting the use of SLT as a first-line therapy in glaucoma.