Selective laser trabeculoplasty (SLT) vs other treatment modalities for glaucoma: a systematic review

Methodological quality of the review: Low confidence

Author: McAlinden C

Geographical coverage: Not reported

Sector: Glaucoma

Sub-sector: Comparing medications

Equity focus: None specified

Review type: Effectiveness review

Quantitative synthesis method: Narrative/thematic synthesis

Qualitative synthesis method: Not applicable

Background: Glaucoma is one of the main prevalent eye diseases characterised by high intra-ocular pressure (IOP), for which reducing IOP remains the only treatment option. Options for treatment depend on the type of glaucoma and include medical therapy (e.g. beta blockers, alpha-agonists, miotics, carbonic anhydrase inhibitors and prostaglandin analogues), laser treatment (e.g. argon laser trabeculoplasty (ALT), selective laser trabeculoplasty (SLT), neodymium-doped yttrium aluminium garnet (Nd:YAG) laser iridotomy, diode laser cycloablation, and laser iridoplasty) and surgery.

SLT was developed following the introduction of selective photothermolysis in dermatology. It utilises a Q-switched, frequency-doubled, 532nm Nd:YAG laser. With this laser, it is possible to selectively target the pigmented cells in the trabecular meshwork, as these cells exhibit greater optical absorbance to the laser than neighbouring cells, hence avoiding collateral damage.

Commercial SLT devices deliver 400 mm diameter laser spots in 3 ns, with typical power settings of 0.4–1.2 mJ. The energy delivered to the eye by SLT is significantly less than that of ALT, which results in less tissue damage to the trabecular meshwork. This review compares SLT to other treatment options.

Objectives: To compare SLT to other treatment options in terms of their IOP-lowering effect.

Main findings: In this study, 23 randomised controlled trials (RCTs) were initially identified via PUBMED with 17 meeting the inclusion criteria. Nine RCTs compared 180º SLT to 180º argon laser trabeculoplasty (ALT) and one trial compared 360º SLT to 360º ALT. There was no difference in terms of IOP reduction from baseline.

One RCT reported better outcomes with SLT at one year, but this effect regressed at two years. Three trials compared 360º SLT to medical therapy and found no difference between the two treatment options. One trial found greater IOP reduction with latanoprost vs 90º and 180º SLT, and greater IOP reduction with 180º and 360º SLT versus 90º SLT, however no differences were found between 360º SLT versus latanoprost or 360º vs 180º SLT.

Two trials compared 180º SLT to 360º SLT finding no difference in IOP reduction. Two trials compared 180º SLT to 90º SLT, one finding no significant difference and one finding greater IOP reduction with 180º SLT over 90º SLT. One trial compared excimer laser trabeculotomy (ELT) to 180º SLT, finding no differences in IOP reduction at three months’ follow-up but greater IOP reduction with ELT at time intervals between nine and 24 months. There were no RCTs identified that compared SLT to surgery.

The author concludes that there is no difference between SLT and ALT. Three trials indicate no difference between 360º SLT and medical therapy, with one of the trials indicating greater IOP reduction with latanoprost over 90º and 180º SLT. Three trials indicate no difference between 180º SLT and 360º SLT. It is inconclusive whether 90º is less efficacious than 180º SLT. One trial reports greater IOP reduction with ELT over 180º SLT in the long term.

Methodology: Authors include RCTs comparing SLT to other treatment options and those comparing different modalities of SLT. RCTs in progress, unpublished, or conference abstracts were not considered. The main outcome measure was the change in IOP from baseline. Other outcomes such as complications or side effects of treatments were not considered.

PUBMED, the Cochrane Central Register of Controlled Trials, Ovid, EMBASE, the metaRegister of Controlled Trials, and ClinicalTrials.gov were searched without date or language restrictions until March 24 2013. The following search terms were used: selective laser trabeculoplasty OR Nd:YAG laser trabeculoplasty OR YAG laser trabeculoplasty OR SLT AND glaucoma.

Authors were contacted by email for clarification in cases where it was not clear from the methodology whether randomisation was performed.

Applicability/external validity: The authors did not discuss applicability/external validity.

Geographic focus: The geographical coverage of included studies is not clear as it was not reported by the authors.

Summary of quality assessment: This systematic review was based on a comprehensive research of relevant databases with no restriction of time or language of publications. However, it has the following major limitation: only one author has identified and assessed the included studies. There were no clear criteria for assessing the quality of the included studies. Authors of relevant articles were contacted for clarification if it was necessary, but it is not clear if the list of references of the relevant papers were checked for relevant articles or not. In addition, authors did not provide a table or a summary of the assessment of the included studies. Therefore, low confidence was attributed in the conclusions about the effect of this study.