Glaucoma Service Foundation Web Blog

Trabs Versus Shunts

Trabs Versus Shunts
Chat from  November 2, 2011
Guest Speaker – Dr. Michael J. Pro
Steven Beck, Editor
Lorraine Miller, Editor, Chat Topic Researcher


On Wednesday, November 2, 2011, Dr. Michael Pro, a glaucoma specialist at Wills, and the glaucoma chat group discussed “Trabs Versus Shunts”.

Moderator: Tonight’s topic is “Trabs Versus Shunts”.

Dr. Pro: Close to my heart!

Moderator: Can you start by describing each?

Dr. Pro: Sure. I am sure that most of you are familiar with these surgeries. Some may even have had them. Trabeculecomy as a surgical technique was first described in the 1960s. The idea was to provide a safer alternative to the glaucoma surgeries of that day. Those surgeries would lead to high levels of complications like flat anterior chambers and cataracts.

The trabeculectomy is essentially the creation of a new drainage pathway for aqueous to pass from the anterior chamber to a space under the conjunctiva (the bleb) from which it would leave the eye. With a trabeculectomy, the defining feature is a scleral flap that helps to modulate the outflow of aqueous and helps to prevent complications such as a flat anterior chamber and hypotony (IOP that is too low). Today we usually do trabeculectomies with anti-scarring medicines like mitomycin C and 5-FU. These medicines help to prevent early healing and fibrosis which can cause trabeculectomies to fail.

P: Why would either of these surgeries be used rather than one of the more non-invasive surgeries currently available?

Dr. Pro: Good question. First, many surgeons are not as familiar with the non-penetrating surgeries. Second, the success of some of those surgeries seems very surgeon and center dependent. Those surgeries have a steeper learning curve. Third, tubes and trabs have a proven track record of success

P: Would you please tell us about “The Tube Versus Trabeculectomy (TVT) Study?”

Dr. Pro: Yes. This is a very important study that compared the surgical results in patients who had tube shunts versus patients who had trabs. This was a multi-center and randomized trial. In other words, if a patient agreed to participate, he or she would be randomized to get either a trab or a tube. The important finding here was that tubes did as well as trabs in terms of final IOP control at three years. But, the tubes needed more glaucoma medications to achieve IOP control than the trabs. The trabs had more complications in the post-operative period.

P: How do the results of the TVT Study affect the treatment of glaucoma?

Dr. Pro: That is interesting. I don’t know yet. My feeling is that for most surgeons, the results won’t change their behavior much. You see, the study didn’t find one surgery to be superior to the other. Also, one can always nitpick on aspects of the study design. In general, if you have been treating glaucoma long enough, you may see every complication from every surgery. I and most glaucoma surgeons try to pick the best surgery for that particular patient.

P: Does having one preclude having the other?

Dr. Pro: No, although the usual course is to start with a trab and then do a tube once that fails. Also the tube surgery usually causes more conjunctival scarring and doing the trab can then be much more difficult. It may, for instance some studies (but not all) suggest a worse outcome for trabeculectomy in African Americans. But perhaps more important is the type of glaucoma. Neovascular and Inflammatory glaucoma are poor candidates for trabeculectomy and usually do better with tube shunts.

P: Was the Scheie sclerectomy an early form of a trab as my mom had one in the early 1970s?

Dr. Pro: Yes, the Scheie procedure was similar to the trab.

P: What is the average effectiveness of each in term of years?

Dr. Pro: Well, again this depends on the study and the amount of time that the patients are followed. In general the success is about 80 percent and is similar to trabs and tubes.

P: This is interesting. I think I heard that one can have repeat trabs. Is this correct? Are there repeat tubes as well?

Dr. Pro: Yes, indeed. In fact one can have as many as three trabs and up to four tubes!

P: What in your estimation is the length of time these procedures remain effective for an uncomplicated patient?

Dr. Pro: Well, since we have been talking about the tube versus trab study we can point to that data to say that tubes are about 85 percent successful at three years and trabs are about 70 percent successful. Other studies have not been quite as negative regarding trabs and show success at 80-85 percent as I have quoted before.

It is difficult to estimate longevity of surgical success. I have many patients whose blebs have been going strong for years. Clinically if the eye is quiet and the IOP has have well controlled, it will continue in that manner.

The criticism of the trab data involves the fact that resident surgeries were included in the study and the MMC application was heavy. That having been said, the TVT is an important study.

Moderator: It’s half past doctor. Thank you once again.

Dr. Pro: OK, great. Nice questions! Good night.


About the Author:

The Glaucoma Service Foundation’s mission is to preserve or enhance the health of all people with glaucoma and to provide a model of medical care by supporting the educational and research efforts of the physicians on the Wills Eye Institute Glaucoma Service, the largest glaucoma diagnosis and treatment center in the country.
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