What are the benefits and risks of different surgical approaches for primary congenital glaucoma (an eye condition that affects children under five years old)?

Why this question is important
Primary congenital glaucoma (PCG) is a rare disease of the optic nerve. It affects children who are under five years old, and is caused by abnormally high pressure in the eye. This develops when the eye’s drainage system does not work properly, and fluid builds up in the eye. The increased pressure in the eye can damage the optic nerve, and cause partial—or even total—blindness.

The most common treatment for PCG is surgery. There are different surgical approaches that aim to decrease pressure in the eye. For example, in goniotomy an incision is made to create an opening on the inside of the eye, through which fluid can drain, while in trabeculotomy an incision is made on the outside of the eye. A third technique, trabeculectomy, involves removing some tissue from the eye to create an opening; this may be combined with trabeculotomy.

As with any medical treatment, each surgical approach for PCG has potential benefits and risks. To find out whether some surgical procedures are more beneficial, or cause more unwanted effects, than others, we reviewed the evidence from research studies.

How we identified and assessed the evidence
First, we searched for all relevant studies in the medical literature. We then compared the results, and summarized the evidence from all the studies. Finally, we assessed how certain the evidence was. We considered such factors as the way studies were conducted, study size, and consistency of findings across studies. Based on our assessments, we categorized the evidence as being of very low, low, moderate, or high certainty.

What we found
We found 16 studies with a total of 446 children with PCG. The children were followed for between six and 80 months after surgery. Eleven studies were conducted in Egypt and the Middle East, three in India, and two in the USA.

Trabeculectomy plus trabeculotomy versus trabeculectomy alone

Three studies (on 68 children) compared trabeculectomy combined with trabeculotomy, against trabeculectomy alone. The studies were poorly conducted and small, and results were inconsistent across the studies (very low-certainty evidence). So, we cannot tell from these studies which surgical approach is more successful or causes fewer unwanted effects.

Viscotrabeculotomy versus conventional trabeculotomy

Two studies (on 39 children) compared viscotrabeculotomy (a type of trabeculotomy that uses a thick liquid to create an opening in the eye’s drainage system) with conventional trabeculotomy. The studies were poorly conducted and small (very low-certainty evidence), so we cannot tell from these studies which surgical approach is more successful or causes fewer unwanted effects.

Trabeculotomy (microcatheter assisted, 360-degree) versus conventional trabeculotomy

Two studies (on 95 children) compared another type of trabeculotomy (microcatheter-assisted 360-degree trabeculotomy)—where an opening is made all around the eye with the help of a very small, hollow tube—against conventional trabeculotomy. The evidence was of moderate certainty, because the studies were well conducted, but small. The evidence suggests that microcatheter-assisted 360-degree trabeculotomy probably reduces eye pressure slightly one year after surgery. Children given this treatment are probably more likely to have normal eye pressure (under 21 mmHg) one year after surgery than those who have conventional trabeculotomy. However, the evidence suggests that they are probably more likely to also experience hyphema, a side effect in which blood collects at the front of the eye, partially or completely blocking vision.

Other surgical procedures

None of the remaining nine trials investigated the same surgical procedures. This means that for many surgical procedures for PCG, such as trabeculectomy on its own or goniotomy, there is too little evidence to determine whether one method is better or causes more unwanted effects than others.

Conclusion
The evidence on the comparative benefits and risks of different surgical procedures for PCG is limited. Microcatheter-assisted 360-degree trabeculotomy is probably more beneficial than standard trabeculotomy, but probably causes more unwanted effects. We do not know the comparative effects of other surgical procedures, as there are either no studies or too few studies that compare them.

How up-to-date is this review?
The evidence in this Cochrane Review is current to 27 April 2020.

Authors' conclusions: 

The evidence suggests that there may be little to no evidence of difference between CTT and routine conventional trabeculotomy, or between viscotrabeculotomy and routine conventional trabeculotomy. A 360-degree circumferential trabeculotomy may show greater surgical success than conventional trabeculotomy. Considering the rarity of the disease, future research would benefit from a multicenter, possibly international trial, involving parents of children with PCG and with a follow-up of at least one year.

Read the full abstract...
Background: 

Primary congenital glaucoma (PCG) is an optic neuropathy with high intraocular pressure (IOP) that manifests within the first few years of a child's life and is not associated with other systemic or ocular abnormalities. PCG results in considerable morbidity even in high-income countries.

Objectives: 

To compare the effectiveness and safety of different surgical techniques for PCG.

Search strategy: 

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (2020, Issue 4); Ovid MEDLINE; Embase.com; PubMed; metaRegister of Controlled Trials (mRCT) (last searched 23 June 2014); ClinicalTrials.gov; and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP). We did not use any date or language restrictions in the electronic search. We last searched the electronic databases on 27 April 2020.

Selection criteria: 

We included randomized controlled trials (RCTs) and quasi-RCTs comparing different surgical interventions in children under five years of age with PCG.

Data collection and analysis: 

We used standard Cochrane methodology.

Main results: 

We included 16 trials (13 RCTs and three quasi-RCTs) with 587 eyes in 446 children. Eleven (69%) trials were conducted in Egypt and the Middle East, three in India, and two in the USA. All included trials involved children younger than five years of age, with follow-up ranging from six to 80 months.

The interventions compared varied across trials. Three trials (on 68 children) compared combined trabeculotomy and trabeculectomy (CTT) with trabeculotomy. Meta-analysis of these trials suggests there may be little to no evidence of a difference between groups in mean IOP (mean difference (MD) 0.27 mmHg, 95% confidence interval (CI) −0.74 to 1.29; 88 eyes; 2 studies) and surgical success (risk ratio (RR) 1.01, 95% CI 0.90 to 1.14; 102 eyes; 3 studies) at one year postoperatively. We assessed the certainty of evidence as very low for these outcomes, downgrading for risk of bias (-1) and imprecision (-2). Hyphema was the most common adverse outcome in both groups (no meta-analysis due to considerable heterogeneity; I2 = 83%).

Two trials (on 39 children) compared viscotrabeculotomy to conventional trabeculotomy. Meta-analysis of 42 eyes suggests there is no evidence of between groups difference in mean IOP (MD −1.64, 95% CI −5.94 to 2.66) and surgical success (RR 1.11, 95% CI 0.70 to 1.78) at six months postoperatively. We assessed the certainty of evidence as very low, downgrading for risk of bias and imprecision due to small sample size. Hyphema was the most common adverse outcome (38% in viscotrabeculotomy and 28% in conventional trabeculotomy), with no evidence of difference difference (RR 1.33, 95% CI 0.63 to 2.83).

Two trials (on 95 children) compared microcatheter-assisted 360-degree circumferential trabeculotomy to conventional trabeculotomy. Meta-analysis of two trials suggests that mean IOP may be lower in the microcatheter group at six months (MD −2.44, 95% CI −3.69 to −1.19; 100 eyes) and at 12 months (MD −1.77, 95% CI −2.92 to −0.63; 99 eyes); and surgical success was more likely to be achieved in the microcatheter group compared to the conventional trabeculotomy group (RR 1.59, 95% CI 1.14 to 2.21; 60 eyes; 1 trial at 6 months; RR 1.54, 95% CI 1.20 to 1.97; 99 eyes; 2 trials at 12 months). We assessed the certainty of evidence for these outcomes as moderate due to small sample size. Hyphema was the most common adverse outcome (40% in the microcatheter group and 17% in the conventional trabeculotomy group), with greater likelihood of occurring in the microcatheter group (RR 2.25, 95% CI 1.25 to 4.04); the evidence was of moderate certainty due to small sample size (−1).

Of the nine remaining trials, no two trials compared the same two surgical interventions: one trial compared CTT versus CTT with sclerectomy; three trials compared various suturing techniques and adjuvant use including mitomycin C, collagen implant in CTT; one trial compared CTT versus Ahmed valve implant in previously failed surgeries; one trial compared CTT with trabeculectomy; one trial compared trabeculotomy to goniotomy; and two trials compared different types of goniotomy. No trials reported quality of life or economic data.

Many of the included trials had limitations in study design, implementation, and reporting, therefore the reliability and applicability of the evidence remains unclear.

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