Battlelines clearly marked out as trabeculectomy and drainage implant surgery go head to head

Ana Hidalgo-Simón MD, PhD
in Gatwick

Bascom Palmer

Steven J Gedde

Richard Parrish

“Glaucoma drainage implants offer an alternative approach to reduce intraocular pressure (IOP) in patients with medically uncontrolled glaucoma, an alternative to trabeculectomy or cyclodestructive procedure. They are being increasingly used for the treatment of refractory glaucoma,” said Steven J Gedde MD, Bascom Palmer, in a lecture introducing the Palmberg-Parrish head-to-head.

Dr Gedde readily acknowledged that both procedures work well and have relatively low complication rates, so much so that it is unclear in certain clinical situations whether one operation is better than the other. He feels that the long-term pressure control will likely be comparable between the two groups.

Dr Palmberg began by noting that the usual glaucoma filtering operations are not working as well as you would like, and in certain circumstances are causing problems, such as infections or hypotony. That prompted the development of an alternative approach in the form of plastic drainage devices.

“At this point, we are rather uncertain which is the best one to use in cases where either one might be applied. We have clearly identified some situations where, in my mind, trabeculectomy is still the better thing to do because it affords the glaucoma lower pressure and more stability, all other things being equal.

“And we think the tubes have great importance in cases where there has been a lot of previous surgery and scarring, or the patient has an infection on the eyelids,” Dr Palmberg said.

He noted that there is strong evidence that lowering pressure to the low teens in patients with advanced glaucoma is most likely to be associated with preservation of the visual field and visual acuity.
A lower pressure with a trabeculectomy, as opposed to drainage implant surgery, is more likely to be achieved.

He reinforced his argument by citing the results of recent clinical trials, such as the Advanced Glaucoma Intervention Study and the Normal Tension Glaucoma Study. That data suggests that in order to get an optimal result, some patients need pressures down around 12mmHg.

He emphasised that such results can best be achieved by doing a filtering operation with an anti-scarring drug, such as mitomycin, or perhaps 5-fluororuacil (5FU). But 5-FU is nowhere near as effective in repeat operations.
He stressed that while age, genetic factors and race are all important in affecting outcomes of glaucoma surgery, pressure control is the crucial element.

Patients with advanced damage and normal tension glaucoma need low normal pressures. But as a comparison of initial glaucoma treatment studies shows, those with mild initial damage may do very well in the middle of the normal pressure range.

Dr Palmberg reminded the listeners that the safety of filtering surgery with antimetabolites could be markedly improved through the use of techniques that produce blebs with a lower profile and that reduce the risk of hypotony-induced vision loss by careful adjustment of the scleral resistance at surgery.

Dr Parrish presented the argument on behalf of drainage implant surgery. He believes that aqueous tube shunt surgery is preferable in glaucoma cases which are difficult to manage, where the patient has undergone previous cataract surgery, trabeculectomy had failed and there is extensive scarring at the limbus.

He cited evidence based on a study by Roy Wilson MD and colleagues of primary filtering surgery vs primary drainage implant surgery (AJO, September 2000), suggesting that the two procedures are comparable.
Moreover, a long-term follow-up has indicated that the results seen after one year have continued for the following two years.

“I think that drainage implant surgery in the difficult glaucomas, those with a great deal of scarring or after failed trabeculectomy, is preferable because it is at least as effective as trabeculectomy.
“And secondly, it is less likely to be complicated with late bleb, late onset infections we frequently see with the use of mitomycin C and 5-FU following the filtering surgery in these difficult management cases,” Dr Parrish said.

He conceded Dr Palmberg’s main point that there is strong evidence to suggest that lowering pressure to the low teens in patients with advanced glaucoma is most likely to be associated with preservation of the visual field and visual acuity, and that one is more likely than not to get a lower pressure with a trabeculectomy, as opposed to drainage implant surgery.

In an interview with EuroTimes, Dr Palmberg remarked on the greater exposure to other doctors’ ideas around the world, like Peng Khaw at Moorfields Eye Hospital, London, UK, one of the leading investigators in wound healing after glaucoma surgery.
He has contributed ideas that have helped Dr Palmberg to markedly reduce the risk of infection after glaucoma surgery.

“Dr Khaw has found ways to reduce the risk of infections from perhaps 8% or 10% down to 1%. Therefore we can make these procedures safer than their overall risk-benefit ratio. And we are finally seeing developments in glaucoma, technical innovations, clever ideas, newer techniques and materials beginning to match the wonderful evolution of cataract surgery.

“The next decade will see people marvelling at how much glaucoma surgery has improved. Just in the last few years in these clinical trials, innovations, new materials, anti-scarring drugs, drainage tubes — we have something to deal with every glaucoma problem so that when we go into the operating room, we have confidence. And this certainly was not the case 20 years ago,” Dr Palmberg said.

Dr Gedde is organising a multicentre randomised five-year clinical trial, called the tube vs trabeculectomy study, to compare the long-term safety and efficacy of an anti-metabolite trabeculectomy to the glaucoma drainage implant using the Baerveldt implant.

Fifteen clinical centres across the US, as well as Moorfields Eye Hospital, have enrolled 170 patients so far, with the aim of reaching 200.
“We are looking at complications, as well as visual field and IOP outcomes. I am not sure what the results are going to show. And when you have a question to which you don’t know the answer, the best thing to do is design a good randomised clinical trial.

“I suspect we are going to see a higher rate of infection associated with trabeculectomy, especially late onset infection. And there will also be other complications unique to glaucoma drainage implants,” Dr Gedde told EuroTimes.
He added that, unfortunately, there is not that much clinical information to guide that decision.

“Hopefully in the future, with the results of the tube vs trabeculectomy study and other studies in the future, we may have some additional information to guide clinicians in choosing the best type of operation for their patients,” he said.

Paul F Palmberg MD, PhD
Bascom Palmer Eye Institute, Miami, Florida, US
Email: ppalmberg@med.miami.edu or mitodoc@aol.com

Richard K Parrish MD
Bascom Palmer Eye Institute, Miami, Florida, US
Email: rparrish@med.miami.edu

Steven J Gedde MD
Bascom Palmer Eye Institute, Miami, Florida, US
Email: sgedde@med.miami.edu

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