Trabeculectomy on the decline as alternative approaches emerge

The TVT study and devices such as the Ex-PRESS mini shunt have demonstrated the viability of nonpenetrating approaches.

Thomas W. Samuelson

The most compelling developments right now in glaucoma are on the surgical front. Obviously, trabeculectomy has been the gold standard, but it is getting squeezed now from all sides.

Why is that? We have better medications now than ever before, including three excellent prostaglandins and better combination medications.

Selective laser trabeculoplasty has also taken a bite out of trabeculectomy. In addition, cataract extraction alone lowers IOP more than previously appreciated.

For the surgical treatment of mild to moderate disease, blebless surgery – including trabecular bypass, canaloplasty (iScience), endoscopic cyclophotocoagulation and the Trabectome (NeoMedix) – is also taking a bite out of trabeculectomy.

Finally, for more advanced disease or cases at greater risk of failure, the Tube Versus Trabeculectomy (TVT) study, done by Steven J. Gedde, MD, at the Bascom Palmer Eye Institute, has suggested that drainage implants may be as good or better than trabeculectomy. Accordingly, more tubes are being performed and have reduced the role of trabeculectomy from the more complex disease side.

Many of the surgical advances in glaucoma are revolutionary. That is, they purport to completely change the way that we do things. For example, Trabectome and iScience canaloplasty are revolutionary procedures. In contrast, there are also procedures that, while maybe not revolutionary or an entirely new approach, are making trabeculectomy better.

I will not spend too much time on the new trabecular bypass approaches to internal filtration because we discussed that last year.

I do want to discuss what we are doing to make transscleral filtration better – the evolutionary things, such as the TVT study and the ExPress mini shunt (Optonol).

TVT study

At Hawaiian Eye 2008, I gave a talk about the TVT study called “Why this Study is More Important than Most People Realize.”

If you look at the data, you can see that tubes are being utilized more frequently by glaucoma surgeons. Drainage implants have several advantages over trabeculectomy. For example, they are less vulnerable to scarring and more amenable to contact lens wear. Tubes are safer inferiorly, an important advantage in many eyes that have had multiple surgeries.

The purpose of the TVT study was to compare the safety and efficacy of nonvalved tube surgery to trabeculectomy. Generally, in the past, you would implant a tube only when you could not perform a trabeculectomy. So tubes were relegated to last-resort status in the most complex eyes.

Many have suggested that tubes should be employed earlier in the treatment scheme. Two landmark articles were published by Dr. Gedde and colleagues in the American Journal of Ophthalmology in January 2007.

This was a well-conceived study. The investigators prospectively randomized 212 patients to one of two groups. Excluding deaths, 97% of the follow-up visits were completed during the first year. So we have great data to evaluate.

The IOP in patients implanted with tubes went from an average of 25 mm Hg preoperatively to 12 mm Hg postoperatively at 1 year follow up. The trabeculectomy group was similar, and the authors found no statistical difference in IOP at the 1-year point.

If you look at probability of failure, defined as pressure greater than 21 mm Hg or less than 5 mm Hg, the trabeculectomy group was much more likely to fail than the tube group in the first 12 months.

In an editorial written when this study was first launched, I predicted that the trabeculectomy group would do better in the first year, but that the tube group would do better later on.

I was surprised to learn that the tube group was as successful as trabeculectomy in the first year. The probability of failure was significantly higher in trabeculectomy than tubes.

Indeed, nonvalved tube surgeries were more likely to maintain IOP control and avoid persistent hypotony and reoperations than trabeculectomy during the first year.

I believe that this study is gaining some traction nationwide. I am doing fewer trabeculectomies now for all the reasons I have discussed earlier, and this study is one important reason that I am definitely doing more tubes. I almost never do a repeat trabeculectomy, preferring tubes in patients who have failed one trabeculectomy. I am also doing tubes on younger patients who may be at risk of hypotonous maculopathy.

In addition, the risk of infection cumulative over a patients’s lifetime is definitely less with a tube than with a bleb.

One cautionary note on the TVT study is that they did not report endothelial cell counts, and there was no diplopia data reported either, an important consideration in patients with good vision in both eyes.

Ex-PRESS mini shunt

Moving to a different evolutionary product, I was on record as calling this procedure “glaucoma roulette” when the Ex-PRESS mini shunt was launched. The recommended technique at launch was to place the device directly under the conjunctiva. Thsi proved to be a dangerous proposition.

But now the standard technqiue is to place the device under the scleral flap, it is a much better procedure, with considerably less risk. You do not open the eye like you do with trabeculectomy; the device is placed via a simple 27-gauge needle tract. You make a standard 50% to 60% depth scleral flap and pop it in through the paracentesis tract in the bed of the flap. The Ex-PRESS is made out of stainless steel, the same material as many cardiac stents, and it is less than 3 mm long.

The company reports more than 22,000 implantations worldwide. While many claim that the Ex-PRESS shunt standardizes the trabeculectomy, really it only standardizes sclerostomy.

The Ex-PRESS goes through a 27-gauge needle tract. This is a safer, more closed system, and you do not run the risk of collapse of the anterior chamber or of vitreous shifting.

This technique represents a simplified approach and is unquestionably easier to teach residents.

I have just recently begun to implant them and have implanted about a dozen of these.

Also, if you are an occasional glaucoma surgeon, this approach is appealing. The more you simplify the approach, the better. And this technique clearly simplifies it.

Again, this is an evolutionary step forward for trabeculectomy — not revolutionary.

In conclusion, I think the trend toward fewer trabeculectomies will continue, but transscleral filtration will not go away. Even though we are doing fewer trabeculectomies, they are still going to be necessary because they provide lower IOP than many of the trabecular bypass procedures or Schlemm’s canal procedures I mentioned earlier. They might be performed in a modified fashion with new devices, but they are here to stay for the foreseeable future.

For more information:

• Thomas W. Samuelson, MD, can be reached at Minnesota Eye Consultants, 710 E. 24th St., Suite 100, Minneapolis, MN 55404; 612-813-3600; fax: 612-813-3636; e-mail: twsamuelson@mneye.com. Dr. Samuelson is a paid consultant for Advanced Medical Optics, Alcon, Allergan, iScience, Denali Medical, Glaukos and Pfizer.

References:

• Gedde SJ, Schiffman JC, et al. Treatment outcomes in the tube versus trabeculectomy study after 1 year of follow-up. Am J Ophthalmol. 2007;143(1):9-22.
• Gedde SJ, Herndon LW, et al. Surgical complications in the Tube Versus Trabeculectomy Study during the first year of follow-up. Am J Ophthalmol. 2007;143(1):23-31.