Healio
Healio
November 25, 2008
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Tube vs. trabeculectomy study

At Issue posed the following question: Has the TVT study influenced your indications for tube shunt surgery?

Study 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 (ie, bleb leaks and bleb infections) has contributed to the increased use of tube shunts as an alternative to trabeculectomy. However, there is lack of consensus among glaucoma surgeons about the best surgical approach in patients with previous ocular surgery. In particular, some surgeons prefer a trabeculectomy with mitomycin C and others favor a tube shunt in patients who have had previous cataract surgery or failed filtering surgery. This was the population that was investigated in the Tube vs. Trabeculectomy (TVT) study to provide additional information to guide surgical decision making.

Steven J. Gedde, MD
Steven J. Gedde

A total of 212 patients who had previous cataract extraction with IOL implantation and/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 (eg, 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. Based upon a review of the existing tube shunt literature, it has been 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 (eg, 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 (eg, 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 and/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 (eg, 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).

References:

  • Chen PP, Yamamoto T, Sawada A, et al. Use of antifibrosis agents and glaucoma drainage devices in the American and Japanese Glaucoma Societies. J Glaucoma. 1997;6:192-196.
  • 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.
  • 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.
  • Minckler DS, Francis BA, Hodapp EA, et al. Aqueous shunts. A report by the American Academy of Ophthalmology. 2008;115:1089-1098.
  • Steven J. Gedde, MD, can be reached at Bascom Palmer Eye Institute, 900 NW 17th St., Miami, FL 33136; e-mail: gedde@med.miami.edu.

Already using shunts more

Nathan G. Congdon, MD, MPH
Nathan G. Congdon

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 which 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.

However, I think there are some issues worth considering in deciding to perform tube shunt vs. trabeculectomy surgery 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, I think that we ought to 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 as physicians do what we can to hold costs down.
  • 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 remind ourselves 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 before deciding to proceed with a drainage device.

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.
  • 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.

Use individualized approach

Robert N. Weinreb, MD
Robert N. Weinreb

Robert N. Weinreb, MD: This landmark study has reported 1-year results suggesting that that treatment of patients with previous trabeculectomy, cataract surgery or other high-risk patients 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 for any practitioner needs to be considered in the context of their own clinical experience.

  • There were a number of unexpected results in this study, including the number of complications in both groups. More than one-half of the patients in the trabeculectomy group had a complication.
  • It is surprising that the IOP-lowering of 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 needs to 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 the results of 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 and alternative 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 similar inclusion criteria as 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.

  • 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.

Indications remain unchanged

Douglas J. Rhee, MD
Douglas J. Rhee

Douglas J. Rhee, MD: Although seemingly “no,” it is only because I have had a relatively low threshold for using traditional cetons/tube shunts (ie, devices that allow direct communication between the anterior chamber and subconjunctival space as well as having a reservoir plate). I have never been a fan of repeat trabeculectomies. Following a failed trabeculectomy, tube shunts lower IOP more reliably than a repeat trabeculectomy, in my hands. I was not surprised by the TVT results. I hypothesize that as longer-term follow up data become available, tube shunts will show superiority with regard to sustained IOP lowering and safety.

My indications for primary tube-shunt surgery remains unchanged.

  • Douglas J. Rhee, MD, is an assistant professor of ophthalmology at Harvard Medical School and on the faculty of the Massachusetts Eye and Ear Infirmary. He can be reached at 243 Charles St., Boston, MA 02144; 617-573-3670; fax: 617-573-3707; e-mail: dougrhee@aol.com.
Louis B. Cantor, MD
Louis B. Cantor

No dramatic changes, yet

Louis B. Cantor, MD: The TVT study has not dramatically altered my practice and indications for tube shunts. Before the TVT I had gained confidence that tube shunts could be performed as a primary or secondary glaucoma procedure with good results. The TVT study has supported my earlier impressions, though I do feel better having more evidence.

  • Louis B. Cantor, MD, can be reached at 702 Rotary Circle, Indianapolis, IN 46202-5175; 317-274-8485; fax: 317-278-1007; e-mail: lcantor@iupui.edu.