TVT Study changing practice patterns in glaucoma surgery

A tube shunt procedure may be preferable to repeat trabeculectomy in cases where the first filter fails.

Issue: February 1, 2007

ByThomas W. Samuelson, MD

Thomas W. Samuelson

In this era of instant gratification, anecdotal reports and uncontrolled or poorly controlled studies seem to dominate the pages of our scientific journals. Accordingly, it seems that a diminishing percentage of published articles truly change the way we practice. Thus, when a researcher makes the effort to conceive, design and execute a well-controlled, prospective, randomized clinical trial, we should take note.

So it is with the Tube vs. Trabeculectomy (TVT) Study, the 1-year results of which were recently published by Steven J. Gedde, MD, and co-investigators. While it will take several years to understand the full implications of this trial, the 1-year results reveal some important findings. Indeed, this trial is already influencing the manner in which I care for my glaucoma patients. (See related article by Dr. Gedde describing the study results.)

The TVT study prospectively compared the outcome of patients randomized to trabeculectomy or to the Baerveldt Glaucoma Implant (Advanced Medical Optics) for aqueous drainage. A year ago in these same pages, I predicted that the early results of this trial would strongly favor trabeculectomy. However, with longer follow-up, I predicted, the implant would reveal the benefits that we have long associated with drainage implants: that is, long term stability, few late complications and a near complete lack of bleb- related infections.

I must admit that I was surprised to see that the Kaplan-Meier survival plot at 1 year revealed a statistically significant difference in favor of the drainage implant. While the longer-term results will eventually speak for themselves, I for one expect the divergence of the two curves to become more apparent over time. As Dr. Gedde observes in the accompanying article, we may be seeing the early signs of a paradigm shift in glaucoma surgery.

Based on the TVT results, I have elevated drainage implants from a procedure that I did only when the conjunctiva and sclera precluded trabeculectomy to a position much higher in my surgical treatment strategy. For example, I rarely perform repeat trabeculectomy any longer. This is a change from my fellowship days at Will’s Eye Hospital, at which time we would place our initial trabeculectomy at the 12-o’clock position so that we could perform repeat surgery, if needed, in either quadrant adjacent to the first surgery. I believe that multiple trabeculectomies in the same eye will likely become an obsolete strategy.

Rest assured there is much still to be done. For example, while the incidence of motility disturbance and strabismus have diminished with the newer implant designs, this and other potential complications of drainage implants such as endothelial cell loss need careful scrutiny before implantation of these devices can dethrone trabeculectomy as the dominant glaucoma surgical procedure.

Fortunately, several excellent studies are under way that will help us answer these questions and also help us select from among the excellent implant designs, including the two most commonly employed drainage implants, the Baerveldt and the Ahmed Glaucoma Valve (New World Medical). In the meantime, the TVT study is an important, well-conceived study that will indeed influence the manner in which we care for our glaucoma patients.

For more information:

Thomas W. Samuelson, MD, can be reached at Minnesota Eye Consultants, 701 E. 24th St., Suite 106, Minneapolis, MN 55404; 612-813-3628; fax: 612-813-3656; e-mail: twsamuelson@mneye.com.

References:

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;143:23-31.

Gedde SJ, Schiffman JC, et al. The Tube Versus Trabeculectomy Study: Design and baseline characteristics of study patients. Am J Ophthalmol. 2005;140:275-287.

Gedde SJ, Schiffman JC, et al. Treatment outcomes in the Tube Versus Trabeculectomy Study after one year of follow-up. Am J Ophthalmol. 2007;143:9-22.