TVT study results have changed practice patterns

Drainage device considered for larger range of patients

Kathy Yang-Williams OD FAAO: The Tube vs. Trabeculectomy (TVT) study has influenced my recommendations for tube shunt surgery. I would traditionally recommend tube shunt surgery for those patients with complicated glaucoma who have failed most other surgical interventions. This would typically include patients who have been treated for uveitic glaucoma, neovascular glaucoma or who have had a history of prior ocular surgery with extensive conjunctival scarring. The TVT has changed my recommendations for tube shunt surgery and I am more likely to consider a glaucoma drainage device (GDD) for a larger range of patients than before.

The TVT was designed to compare outcomes for a particular group of patients: those with medically uncontrolled glaucoma who had previously undergone trabeculectomy or cataract extraction with IOL implantation. So, the results have to be interpreted based on the fact that these procedures were performed by experienced glaucoma surgeons on a select patient population and that these results cannot be extrapolated to other patient groups, that is, complicated glaucoma patients or virgin eyes.

Kathy Yang-Williams

Even though IOP at the end of 1 year was similar in the tube and trabeculectomy groups, the number of medications required to achieve this outcome was higher in the tube group. There were more complete successes, that is, no adjunctive medications required, in the trabeculectomy group. Therefore, patients who require better IOP control without medications in the first year following surgery (those at high risk for progression and intolerant to medications or those who have a history of poor compliance with medications) might be better served by undergoing trabeculectomy rather than a tube procedure when IOP is considered alone.

However, if a patient responds to topical medications and is able to comply with adjunctive treatment, a tube may be more appropriate – the IOP outcome at 1 year was similar between the two groups and there were fewer postoperative complications following a GDD.

Overall, the TVT has helped me see that the IOP can be decreased after a tube shunt procedure to the same degree as that achieved by trabeculectomy with mitomycin C and that, in the hands of an experienced glaucoma surgeon, patients may experience fewer postoperative complications with a GDD than a bleb. Future results and long-term analysis will help us determine which treatment provides the best IOP control with the fewest complications and affords the best quality of life for our patients.

For more information:

• Kathy Yang-Williams, OD, FAAO, can be reached at Roosevelt Vision Source, 7001 Roosevelt Way NE, Seattle WA 98115; (206) 527-2987; fax: (206) 526-8076; e-mail: kyangwilliams@q.com.

Shifted practice pattern

Steven J. Gedde, MD: Tube shunts have traditionally been reserved for eyes at high risk of failure with standard filtering surgery. A growing concern about the late complications associated with trabeculectomy (i.e., bleb leaks and infections) has contributed to the increased use of tube shunts. However, there is lack of consensus among glaucoma surgeons about the best surgical approach in patients with previous ocular surgery.

Steven J. Gedde

In particular, some surgeons prefer a trabeculectomy with mitomycin C and others favor a tube shunt. This was the population that was investigated in the TVT study.

A total of 212 patients who had previous cataract extraction with IOL implantation or failed filtering surgery were enrolled in the TVT study and randomized to placement of a 350-mm2 Baerveldt glaucoma implant or trabeculectomy with MMC (0.4 mg/mL for 4 minutes). The 1-year results showed several surprising findings.

First, tube shunt surgery had a significantly higher success rate (96.1%) than trabeculectomy with MMC (86.5%) using prospectively defined criteria for success and failure that were similar to other glaucoma surgical trials. Second, significantly more patients experienced postoperative complications following trabeculectomy with MMC (57%) than tube shunt surgery (34%). Most of the surgical complications were transient and self-limited (e.g., choroidal effusions and shallowing of the anterior chamber), and the rate of serious complications resulting in reoperation or loss of vision were similar with both procedures. Third, similar low levels of IOP were observed after both surgical procedures, with a greater use of adjunctive medical therapy following tube shunt surgery compared with trabeculectomy with MMC.

Existing tube shunt literature has suggested that low levels of IOP cannot generally be achieved with these devices. However, this is not supported by the TVT study, which found an average IOP of 12.4 mm Hg in the tube group at 1 year.

The greater efficacy of tube shunt surgery in the TVT study compared with other studies may relate to refinements in surgical technique as well as differences in study populations. The TVT study excluded several secondary glaucomas with poor surgical prognoses (e.g., neovascular glaucoma) that were included in other case series of tube shunts, and this study enrolled patients at lower risk of failure than have historically undergone tube shunt surgery (e.g., prior clear cornea cataract extraction).

The TVT study supports an expanded use of tube shunts beyond just high-risk refractory glaucomas. I now commonly place a tube shunt in patients who have had prior cataract extraction or failed filtering surgery, whereas previously I routinely performed a trabeculectomy with MMC.

A similar shift in practice pattern has been observed among other members of the American Glaucoma Society (AGS). A survey of AGS members in 1996 indicated that approximately 93% of glaucoma specialists would perform a trabeculectomy with MMC in eyes with prior cataract or glaucoma surgery. When AGS members were resurveyed in 2007, about 50% still preferred a trabeculectomy MMC while 50% favored placement a tube shunt in eyes with previous cataract or glaucoma surgery.

The results of the TVT study have prompted the launch of another multicenter randomized clinical trial. The Primary Tube vs. Trabeculectomy (PTVT) study is designed to compare the long-term safety and efficacy of tube shunt surgery and trabeculectomy as a primary glaucoma surgical procedure. Patients with low-risk glaucomas (e.g., primary open-angle glaucoma, pigmentary glaucoma, pseudoexfoliation glaucoma) without previous incisional ocular surgery are presently being randomized to placement of a 350-mm 2 Baerveldt glaucoma implant or trabeculectomy with MMC (0.4 mg/mL for 2 minutes).

For more information:

• Steven J. Gedde, MD, can be reached at Bascom Palmer Eye Institute, 900 NW 17th St., Miami, FL 33136; e-mail: sgedde@med.miami.edu.

References:

• Gedde SJ, Herndon LW, Brandt JD, 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, Feuer WJ, 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, Feuer WJ, et al. Treatment outcomes in the Tube Versus Trabeculectomy Study after one year of follow-up. Am J Ophthalmol. 2007;143:9-22.

Already using shunts more

Nathan G. Congdon, MD, MPH: The TVT study’s two main publications suggest that the Baerveldt tube shunt may be at least as safe and effective as trabeculectomy surgery among patients with previous surgery (which might only include phacoemulsification). This is a group of patients for whom many glaucoma specialists might have performed trabeculectomies in the past. I expect that these results will likely accelerate a trend that had already seen trabeculectomies decline by 53% and tube shunts increase by 184% among Medicare beneficiaries in the decade prior to the TVT. The fact is that prior to the TVT, I was already performing more tube shunts than trabeculectomies, probably an indication of the tertiary-care nature of my practice as much as anything else.

Nathan G. Congdon

However, some issues are worth considering in the post-TVT world. In the first place, the basic message of TVT from my perspective was one of equivalency between the procedures. In patients where either procedure would do, we should have a specific justification for using a several-hundred-dollar device where similar results might be achieved without one. While some of us may associate such thinking with “bean counters” and resent its intrusion into clinical practice, in a world where every trend (an aging population, the constant discovery of new procedures and medications) mandates rising medical costs, it is increasingly responsible and appropriate that we do what we can to contain costs.

The TVT was conceived and directed by some of the most respected names in academic glaucoma, participants were drawn from the top clinical centers and the results published in outstanding peer-reviewed journals. We take nothing away from any of these individuals and institutions when we note that the TVT was funded in part by the manufacturer of the Baerveldt shunt.

A recent study of postoperative adverse outcome after glaucoma surgery among Medicare beneficiaries has reported a significantly higher incidence of endophthalmitis, retinal detachment and blindness among patients receiving tube shunts as compared to filtration surgery, with the differences widening over 6 years of follow-up. As the authors themselves point out, these results may reflect unmeasured differences in case severity between the two surgical groups, but they certainly bear further investigation.

I continue to perform a large number of tube shunt surgeries in my practice, but now, as before the TVT, I weigh my options carefully.

For more information:

• Nathan G. Congdon, MD, MPH, can be reached at the Department of Ophthalmology and Visual Science, Chinese University of Hong Kong; e-mail: ncongdon1@gmail.com.

References:

• Ramulu P, Corcoran KJ, Corcoran SL, Robin A. Utilization of various glaucoma surgeries and procedures in Medicare beneficiaries from 1995 to 2004. Ophthalmology. 2007;114:2265-70.

• Stein JD, Ruiz D, Belsky D, Lee PP, Sloan FA. Longitudinal rates of post-operative adverse outcomes after glaucoma surgery among Medicare beneficiaries 1994-2005. Ophthalmology. 2008;115:1109-1116.

Use individualized approach

Robert N. Weinreb, MD: The 1-year results of this landmark study suggest that patients with previous trabeculectomy, cataract surgery or other high risk do better with a Baerveldt glaucoma drainage implant than with another trabeculectomy performed with adjunctive mitomycin C (higher success and fewer complications). The clinical relevance of these results should be considered in the context of the practitioner’s own clinical experience.

Robert N. Weinreb

A number of unexpected results were seen, including the number of complications in both groups. More than half of the patients in the trabeculectomy group had a complication.

It is surprising that the IOP in the trabeculectomy group was not lower after 1 year. This is not consistent with my own trabeculectomy results.

The relevance today to many of the included patients, in view of current cataract surgery techniques that do not violate the conjunctiva (via clear corneal incision), also should be considered.

Many surgeons, including myself, perform trabeculectomy with a small fornix-based conjunctival flap. If the surgery fails, trabeculectomy can be readily performed again in a nearby location, as most of the superior conjunctiva is still readily accessible. In contrast, placement of the current generation of glaucoma drainage devices violates at least one quadrant (and often more) of conjunctiva, and performing another surgical procedure superiorly may be more challenging. In this circumstance, inferior placement of such a device may be preferable.

Glaucoma success should be measured in years and not 12 months. Although 3- to 5-year results are eagerly awaited, glaucoma surgery is undergoing considerable change. One will need to reassess the long-term TVT study results when they are available with new approaches to trabeculectomy, improved drainage devices and new approaches to glaucoma surgery.

The TVT study results have increased my awareness of how successful surgery with a glaucoma drainage implant can be when performed by an experienced surgeon. My surgical approach individualizes treatment options. For most patients with inclusion criteria similar to the TVT study, I still prefer a trabeculectomy with an adjunctive antimetabolite when the target pressure is low. In other circumstances, including higher target IOP, patient lifestyle and ability to be followed, I might instead place a drainage implant.

For more information:

• Robert N. Weinreb, MD, can be reached at University of California-San Diego/Hamilton Glaucoma Center 0946, 9500 Gilman Dr., La Jolla, CA 92093-0946; e-mail: Weinreb@eyecenter.ucsd.edu.