Key messages

• Aqueous shunt might achieve greater qualified success than trabeculectomy, but the certainty of the evidence is low.
• It is not clear whether aqueous shunt compared to trabeculectomy, has any effect on intraocular pressure or whether it decreases complete success, increases visual impairment or decreases the need for reoperation, because the certainty of the evidence is very low.
• Similarly, regarding the safety profile, it is not clear whether aqueous shunt increases the anterior narrow chamber, the persistent corneal edema or the choroidal effusion, because the certainty of the evidence is very low.

What is the evidence.
See evidence matrix  in Epistemonikos later

We found five systematic reviews [1], [2], [3], [4], [5] including nine primary studies reported in 16 references [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], of which four correspond to randomized controlled trials, reported in 11 references [7], [8], [9], [10], [11], [12], [13], [16], [17], [20], [21]. However, one trial [16] was performed in pediatric population with aphakic glaucoma, which is not considered comparable with the rest of patients, so it was excluded from this analysis.

This table and the summary in general are based on three randomized trials [10], [20], [21], since the inclusion of the observational studies did not increase the certainty of the evidence or added additional information.

What types of patients were included*

All trials included patients with glaucoma, with an average age of 53.9 years, of both genders, with average IOP of 25.96 mmHg (25.46 mmHg in the aqueous shunt arm, and 26.45 mmHg in the trabeculectomy arm).

Regarding the type of glaucoma, one trial included patients with primary open-angle glaucoma, chronic angle-closure glaucoma, pseudoexfoliative glaucoma, pigmentary glaucoma [10], one trial included patients with primary open-angle glaucoma, primary angle-closure glaucoma, neovascular glaucoma, uveitic glaucoma and traumatic glaucoma [20] and one trial included primary open-angle glaucoma and angle-closure glaucoma [21].

In terms of the severity of glaucoma, all trials included patients with indication for surgical treatment [10], [20], [21]. One trial included patients both refractory to medical management and to surgical management (previous trabeculectomy, cataract extraction surgery, or both) [10]. One trial included patients refractory to medical management, and a proportion of patients refractory to surgical management (29.0% in the aqueous shunt arm, 43.6% in the trabeculectomy arm, without specifying the type of previous surgical intervention) [20]. One trial included only patients refractory to medical treatment, excluding patients with previous intraocular surgery [21].

What types of interventions were included*

All trials compared aqueous shunt with trabeculectomy [10], [20], [21].

As aqueous shunt, two trials used the Ahmed valve [20], [21] and one trial used the Baerveldt implant [10].

Regarding the use of mitomycin C (MMC), in two trials its use was at the discretion of the surgeon (both arms) [20], [21] and in one trial a 0.4 mg/ml solution was used for 4 minutes in the trabeculectomy arm [10]. 

What types of outcomes
were measured

The trials evaluated multiple outcomes, which were grouped by the systematic reviews as follows:

• Average IOP at the end of follow-up.
• Percentage reduction of postsurgical IOP.
• Absolute reduction of postsurgical IOP.
• Qualified success (objective IOP independent of the use of medical treatment).
• Complete success (objective IOP without the need of medical treatment).
• Complications (narrow anterior chamber, choroidal effusion, hyphema, persistent corneal edema, cystic macular edema, bleb filtration, encapsulated bleb, endophthalmitis, corneal ulcer, dysesthesia, persistent diplopia, hypotony, hypotonic maculopathy, implant exposition, tube deviation, retinal detachment and suprachoroidal hemorrhage).
• Need of reintervention.
• Number of drugs used in the postoperative period.
• Decrease in visual acuity.
• Decrease in visual field.

The average follow-up of the trials was 40 months, with a range between 12 and 60 months.

To whom this evidence does and does not apply

• The evidence presented in this summary applies to patients with glaucoma with indication for surgical treatment. 
• The patients included in the trials were adults. Because of this, the results should be extrapolated cautiously to the pediatric population, in the absence of direct evidence.

• The outcomes of intraocular pressure, complete success, qualified success, visual acuity change and reintervention were chosen because they are considered critical for surgery success. In addition, outcomes related to complications of surgery were chosen as safety parameters of the intervention. This selection is based on the opinion of the authors of the summary, but in general coincide with the outcomes reported in the systematic reviews identified.

• Aqueous shunt might achieve greater qualified success than trabeculectomy. However, it is not possible to conclude about other outcomes, both from the point of view of efficacy and safety profile, due to a very low certainty of the evidence.
• Therefore, it is not possible to make an adequate balance between benefits and risks due to the limitations of the existing evidence.

• None of the systematic reviews considered an economic analysis within its outcomes. However, even if this information were available, the certainty of the evidence on its effects does not currently allow us to make any conclusions regarding the cost-benefit of the intervention.

• Aqueous shunt is used by most of the clinicians in patients whom trabeculectomy has failed or have some types of glaucoma with a high risk of failure. However, this technique is used by a minority of the clinicians as primary surgery for the treatment of glaucoma.
• It is unlikely that the limited certainty of the existing evidence could be a determining factor that leads to variations in the decision-making.

Differences between this summary and other sources

• The systematic reviews reach similar conclusions to those presented here. Among the systematic reviews evaluated, it is important to highlight three systematic reviews [1], [4], [5], since these evaluated all three randomized trials used in this analysis.
• The main clinical guidelines recommend the use of aqueous shunt in patients who are refractory to trabeculectomy, in those at high risk of it [22], [24] or in patients with moderate or advanced glaucoma as a primary alternative to trabeculectomy [23], [24]. However, this guidelines do not make a comparison regarding the effectiveness or safety profile between both surgical techniques.

• There is a high probability that future research changes the conclusions of this summary due to the existing uncertainty of the evidence.
• We found one randomized trial [25] that is not included in any systematic review, that compares the efficacy and safety of aqueous shunt (Baerveldt implant) against trabeculectomy (trabeculectomy with mitomycin C). In addition, there are at least three ongoing trials in the International Clinical Trials Registry Platform of the World Health Organization [26], [27], [28].
• Systematic reviews that include this new evidence could shed new light on this question. However, we did not identify any in progress in the International Prospective Register of Systematic Reviews (PROSPERO) of the National Institute for Health Research.