The case for trabulectomy

Trabeculectomy outcomes are improving, but more 
progress is needed.

Howard Larkin

Posted: Saturday, February 1, 2020

While comparing data over time is problematic, recent studies suggest that trabeculectomy has become safer with improved intraocular pressure (IOP) control over the last 20 years, James Kirwan MA, MBBS, FRCOphth, told the Glaucoma Day at the 37th ESCRS Congress in Paris. Better trabeculectomy outcomes are important because patients are living longer, leaving much more time for patients with advanced or progressive disease to lose vision, he added.
“Trabeculectomy is still, in my view and I think in most people’s view, the most efficacious surgical procedure for glaucoma, particularly when we are looking at long-term data. It’s the only option that I am aware of that has any evidence to show it actually deals with progression of the disease,” said Mr Kirwan, who is a Consultant ophthalmologist at the Portsmouth Hospitals NHS Trust, UK.

Early development

The origins of trabeculectomy date to the mid-19th Century, Dr Kirwan said. Mackenzie described paracentesis in 1854, though the procedure was ineffective. A few years later De Wecker developed anterior sclerotomy.
In the 1960s, H Saul Sugar MD coined the term “trabeculectomy” for a procedure removing a portion of the trabecular meshwork and scleral spur, leading to temporary IOP reduction. In 1967, JE Cairns described trabeculectomy as a ‘guarded fistula’ that enabled controlled aqueous drainage, reducing pressure without complications in some cases.
The procedure was refined throughout the 1970s to the 1990s, and became reasonably effective, particularly in populations that had not had extensive treatment with topical drop therapy, Mr Kirwan said. Multiple studies showed 60-to-90% of trabeculectomy patients achieving less than 21mmHg IOP for periods of five-to-15 years, though complications were common. By the 1990s, use of antimetabolites was also changing the paradigm.

21st-Century experience
Early in this century, the significant increase in the uptake of anti-metabolites such as mitomycin-C and 5-fluorouracil improved success rates in most cases, but also increased complications, including hypotony maculopathy and bleb infection risk. An early review suggested that trabeculectomy infection rates could be as high as 2.8% per year with other studies suggesting a 1% per year risk. More recent studies make clear that this is a marked overestimate. Infection rates ranging from 0.1-to-0.2% per year have been reported in recent series. “So, there is progress, here,” he said.
How much progress is difficult to quantify for several reasons, particularly when evaluating efficacy, Mr Kirwan said. Lack of a common definition of procedure success is a major problem – one review of 100 studies found 92 different definitions with rates varying from 36-to-98% for the same studies. The WGA guidelines have been written to help address the challenges in fairly describing outcomes.
Success rates also tend to reflect the type of study and author intentions, Dr Kirwan added. They generally are higher in case series, where the surgeon is presumably happy with the results (often, now with long follow-up); than in randomised clinical trials, where trabeculectomy is used as a comparator to a commercially supported new innovation and the investigators are presumably looking for a better alternative than their own trabeculectomy outcomes. Most studies are also too short-term to assess results he added.
Other factors complicating efficacy comparisons over time include the greater use of more effective IOP-lowering drugs today, the downward migration of the level of IOP deemed successful, changing indications for surgery and increased combined surgery. Differing anti-metabolite regimens and changes in non-penetrating therapy further complicate historical efficacy comparisons, Dr Kirwan noted.
Evidence for improved safety is stronger. A 2002 audit in the UK found hyphema, shallow anterior chamber and hypotony in about one-quarter of patients each, with visual acuity loss of more than one line, cataract or wound leak each occurring at about one-in-five. The 2013 ‘Trabeculectomy in the 21st Century’ report published in Ophthalmology found complications greatly reduced, with hyphema and hypotony in single digits, shallow AC under 1% and visual loss at 13%. Hypotony maculopathy fell to less than 1%. Only cataracts were more common, at 29%, though this may be due to changes in treatment thresholds over time, Dr Kirwan said.
For the future, Dr Kirwan looks to better control of wound healing, possibly with anti-VEGF agents, and better training to improve outcomes. He called for more research to generate better evidence to support better care.

James Kirwan

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