Key messages

• Selective laser trabeculoplasty results in less intraocular pressure reduction than medical treatment in patients with open angle glaucoma or ocular hypertension.
• It is not clear if there are differences in treatment success rate or need of additional antiglaucomatous interventions, because the certainty of the evidence is low.
• Both therapeutic alternatives are safe and cost-effective in certain settings. If there is optimal adherence, prostaglandin analogues might be the better option.
• However, regarding the outcome of absolute intraocular pressure reduction there are different results in published systematic reviews. This discrepancy is mainly due to differences in the primary studies included for meta-analysis.
• These results are in agreement with the main clinical guidelines, which suggest medical treatment as preferred initial therapy, considering laser trabeculoplasty as valid option in selected patients.

What is the evidence.
See evidence matrix  in Epistemonikos later

We found four systematic reviews [7],[11],[12],[13] that include four randomized clinical trials [14],[15],[16],[17] and one non randomized prospective study [18]. In this table and the summary in general, we only considered the randomized trials.

What types of patients were included

All of the randomized clinical trials included patients with ocular hypertension or primary open angle glaucoma. Two of them included also patients with secondary open angle glaucoma, particularly pseudoexfoliation glaucoma [14],[17] and pigment dispersion syndrome [17]. Only one study included patients with mixed mechanism open angle glaucoma with a narrow angle, if laser peripheral iridotomy was performed more than three months ago, but this study did not report the number of patients included with this diagnosis [14].

All the studies included newly or recently diagnosed patients. Two of them also included patients previously controlled with medical treatment [14],[17].

There is no distinction by sex. Only two studies restricted age as inclusion criteria: one of them considered only patients under the age of 80 [16]; the other included patients between 25 and 82 years [14].

All the studies excluded patients with previous laser procedure or ocular surgery disturbing the aqueous outflow.

Three of the randomized clinical trials considered pregnancy as exclusion criteria [14],[15],[16].

Studies included patients that belong to multiple ethnic groups: Chinese population [15], African or afro-Caribbean [17], white [14],[17] or non-white [14].

What types of interventions were included

All the studies compared selective laser trabeculoplasty with medical treatment.

Regarding laser trabeculoplasty, all randomized clinical trials used similar procedures, with energy ranging from 0,2 to 1,7 mJ per application, adjusted according to patients characteristics and response, and applied over 360 degrees (approximately 100 non-overlapping laser spots).

Regarding the extent of trabecular meshwork treated, one study [17] randomized patients into four groups, one receiving medical treatment, and other three groups treated with selective laser trabeculoplasty in different extent of trabecular meshwork: 360º, 180º and 90º respectively. This differs from the other three randomized clinical trials [14],[15],[16], which applied selective laser trabeculoplasty over 360º of trabecular meshwork. Only treatments performed over 360 degrees were considered for this summary.

Medical treatment modality varied across studies. Two of the randomized clinical trials [16],[17] used exclusively latanoprost, a prostaglandin analogue. One study used [15] a variable combination of medicines including latanoprost, beta-blocker, pilocarpine and dorzolamide. The other randomized clinical trial [14] applied a flexible algorithm of treatment with sequential steps starting with prostaglandin analogues, then adding or substituting to beta-blocker, then brimonidine, and finally dorzolamide, brinzolamide or a fixed-combination dorzolamide-timolol.

What types of outcomes
were measured

The systematic reviews included here, analysed the following outcomes: absolute intraocular pressure reduction [7],[19], treatment success rate [7],[19] and need of additional antiglaucomatous interventions [19].

There is heterogeneity in treatment success definition: one primary study [16] defined it as achieving an intraocular pressure reduction of 20% or more; other study [17] used two definitions, considering intraocular pressure reduction of 20% and 30% from baseline; one study [14] defined treatment success when achieving a target intraocular pressure reduction calculated by using a formula; other [15] defined it indirectly considering treatment failure when intraocular pressure was greater than 21 mmHg in follow up.

To whom this evidence does and does not apply

• This evidence applies to patients with newly diagnosed open angle glaucoma or ocular hypertension, regardless of baseline intraocular pressure or patient age at disease presentation.
• This evidence excludes patients with previous laser procedure or ocular surgery disturbing the aqueous outflow as well as pregnant patients.

• Evidence about patients' preferences in glaucoma treatment shows that visual outcome related to the risk of moderate visual loss (defined as inability to drive a car) and long-term blindness are the most important events that patients want to prevent. There is no clear preference about the treatment modality used, whether medical or surgical [20].
• Despite the fact that visual outcome is not systematically measured in the primary studies included in this review (just one evaluated visual field and visual acuity), there is evidence that intraocular pressure reduction significantly delays progression of glaucoma, including visual field impairment [21].
• The outcomes measured by these studies are centred on intraocular pressure, a very relevant factor used in clinical practice to define treatment success or need of further therapy, especially in patients with early stages of disease to whom this evidence may apply.
• However, it would be ideal to count with primary studies of longer follow up and systematically measuring relevant outcomes such as visual acuity, visual field, cup/disc ratio and adverse effects. 

• In this evidence there is no report of relevant adverse effects for the therapies evaluated, so they may be both considered safe alternatives.
• Nevertheless, there are case reports and series that describe adverse effects of selective laser trabeculoplasty such as subconjunctival haemorrhage, hyphema, corneal haze, cystoid macular edema, choroidal effusion, and more. Most of them were transient or could be resolved with simple medication [7].
• One of the most important side effects reported for laser trabeculoplasty is peripheral anterior synechiae because they are not reversible through medical treatment and could lead to an impaired intraocular pressure reduction effect. Fortunately it is a rare event with selective laser trabeculoplasty [7].

• While medical treatment needs life-long application, selective laser trabeculoplasty could substitute or reduce the number of medications required to achieve disease control [7] hence decreasing treatment costs while the effect of the procedure persists. However, the costs of the laser device acquisition and mainteinance should also be considered.
•  From a patient out of pocket payments perspective, specially in a resource limited setting, the strategy of a one-time laser surgery intervention following self-referral could be highly cost-effective [22]. However, in an optimal adherence setting, prostaglandin analogues would have better cost-effectiveness to treat patients with newly diagnosed open angle glaucoma [23]. 

Differences between this summary and other sources

• Our conclusions regarding treatment success rate are concordant with the identified systematic reviews [7],[11],[12],[19].
• However, regarding absolute intraocular pressure reduction there are differences in the results obtained by the different published meta-analyses [7],[11],[19]. Our results are in agreement with one of the systematic reviews [19], but differ from other two [7],[11]. This is mainly due to differences in the primary studies included in the meta-analysis for this outcome. Both of the systematic reviews that obtained results discordant to ours [7],[11] excluded one of the randomized clinical trials [17] and one of these reviews [11] also included a non-randomized prospective study [18]. The other meta-analysis concordant to our results [19], did not consider one of the primary studies [16]. Our review is the only one including data of the four published randomized clinical trials in the meta-analysis for this outcome.
• Our conclusions are consistent with the main clinical guidelines of glaucoma management. In summary, they suggest medical treatment as first line therapy, but that laser trabeculoplasty can be considered as initial therapy in selected patients, especially who cannot or will not use medical treatment [1],[24],[25],[26],[27],[28].

• It is unlikely that the results of absolute intraocular pressure reduction change substantially in the future because the high certainty of evidence.
• New studies could clarify if there are differences in treatment success rates or need of additional antiglaucomatous interventions. We are not aware of ongoing studies answering this question.