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TVT Study 1-year results suggest greater role for tube shunts
Patients treated with tube shunt surgery were more likely to maintain IOP control and avoid hypotony compared with trabeculectomy.
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| Steven J. Gedde |
A paradigm shift is occurring in glaucoma surgery. Recent surveys of American Glaucoma Society members have shown an increase in the use of tube shunts, also called glaucoma drainage devices, and a decline in the popularity of trabeculectomy. Medicare data demonstrate a steady reduction in the number of trabeculectomies performed during the past decade with a concurrent rise in tube shunt surgery. (See related article for a commentary by Thomas W. Samuelson, MD, on the TVT study.)
A growing concern about the risk of late-onset complications, including bleb leaks and bleb infections, is a likely factor contributing to the shift away from trabeculectomy and toward tube shunt surgery. Tube shunts have traditionally been reserved for glaucomas at high risk for failure with trabeculectomy, such as eyes with neovascular glaucoma and extensive conjunctival scarring. However, the efficacy of these devices has prompted many surgeons to use them in less refractory cases, including pseudophakic eyes and those with failed filters.
Study design
The Tube vs. Trabeculectomy (TVT) Study is a multicenter, randomized clinical trial designed to compare the safety and efficacy of tube shunt surgery with trabeculectomy with mitomycin-C (MMC) in eyes with previous ocular surgery.
Eligible patients were 18 to 85 years old and had undergone previous trabeculectomy and/or cataract extraction with IOL implantation and uncontrolled glaucoma with IOP of between 18 mm Hg and 40 mm Hg on maximum tolerated medical therapy. The study had multiple exclusion criteria, including no light perception vision, pregnant or nursing women, several secondary glaucomas (ie, neovascular glaucoma, uveitic glaucoma, iridocorneal endothelial syndrome, epithelial or fibrous downgrowth), aphakia, vitreous in the anterior chamber, severe posterior blepharitis, unwillingness to discontinue contact lens use, previous cyclodestruction, prior scleral buckling procedure, presence of silicone oil, conjunctival scarring precluding a trabeculectomy superiorly, and need for glaucoma surgery combined with other ocular procedures or an anticipated need for additional glaucoma surgery.
Enrolled patients were randomly assigned to treatment with a 350-mm 2 Baerveldt glaucoma implant (Advanced Medical Optics) placed superotemporally or a superior trabeculectomy with MMC (0.4 mg/mL for 4 minutes). Follow-up visits were scheduled 1 day, 1 week, 1 month, 3 months, 6 months, 1 year, 18 months, 2 years, 3 years, 4 years and 5 years postoperatively. Failure was prospectively defined as IOP greater than 21 mm Hg or not reduced by 20% below baseline on two consecutive visits after 3 months, IOP 5 mm Hg or less on two consecutive visits after 3 months, re-operation for glaucoma or loss of light perception vision.
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Images: Gedde SJ |
Baseline characteristics
A total of 212 eyes of 212 patients were enrolled at 17 clinical centers; there were 107 in the tube group and 105 in the trabeculectomy group. The mean age of the study population was 71 years, and 53% were women. The baseline IOP was 25.3 ± 5.3 mm Hg (mean ± SD), and 81% of patients had primary open-angle glaucoma. There were no significant differences in any of the demographic and ocular characteristics between the tube group and the trabeculectomy group, suggesting that randomization was effective in creating two balanced treatment groups.
Treatment outcomes
There was excellent retention of patients during the first year of follow-up in the TVT Study, and 96.7% of possible follow-up visits were completed. The Table presents the IOPs and number of glaucoma medications at baseline and 1 year. The trabeculectomy group had significantly lower mean IOPs than the tube group at all follow-up visits during the first 3 months, but there were no significant differences between the study groups at 6 months and 1 year.
There was a significantly greater need for supplemental medical therapy in the tube group compared with the trabeculectomy group at all follow-up visits. Kaplan-Meier plots of the probability of failure are shown in the Figure. The cumulative probability of failure was 3.9% in the tube group and 13.5% in the trabeculectomy group at 1 year, a difference that was statistically significant.
| Table. IOP and medical therapy in the TVT Study
Data are presented as mean ± standard deviation. |
Surgical complications
There were a large number of surgical complications during the first year of follow-up in the TVT Study, but most were transient and self-limited. The incidence of intraoperative complications was similar between the tube group (7%) and the trabeculectomy group (10%). Significantly more patients in the trabeculectomy group (57%) experienced postoperative complications compared with the tube group (34%).
The most common complications were choroidal effusions, shallowing of the anterior chamber and wound leaks. The incidence of most postoperative complications was similar in the two treatment groups, but wound leaks and dysesthesia occurred with significantly greater frequency in the trabeculectomy group than the tube group. All complications are not equal in severity, and the rate of serious complications resulting in reoperation or vision loss was similar in the tube group (17%) and the trabeculectomy group (27%).
There was a reduction in visual acuity in the tube group and the trabeculectomy group during the first year of follow-up, but acuity on the Snellen and Early Treatment Diabetic Retinopathy Study charts were similar between treatment groups at 1 year. Patients who developed surgical complications had significantly greater loss of Snellen acuity than patients without complications.
Conclusions
The results of the TVT Study suggest that the role of tube shunts could be expanded beyond the management of only refractory glaucomas. In eyes with previous cataract and/or glaucoma surgery, the study found that tube shunt surgery was more likely to maintain IOP control and avoid persistent hypotony or re-operation for glaucoma compared with trabeculectomy with MMC during the first year of follow-up. Tube shunt surgery and trabeculectomy with MMC produced similar IOP reduction at 1 year, although tube shunts required more supplemental medical therapy. The incidence of postoperative complications was higher after trabeculectomy with MMC than with tube shunt surgery, but serious complications resulting in re-operation and/or vision loss occurred with similar frequency with both surgical procedures.
The TVT Study does not demonstrate clear superiority of one glaucoma operation over the other. There are other factors that must be considered when selecting a surgical procedure, including the surgeon’s skill and experience with both operations and the patient’s tolerance of medications and compliance with therapy, as well as the patient’s access to medications.
Additional follow-up data, which are forthcoming, are needed to fully assess the risks and benefits of tube shunt surgery and trabeculectomy with MMC in managing medically uncontrolled glaucoma in similar patient groups.
For more information:
- Steven J. Gedde, MD, is an associate professor of ophthalmology and the residency program director at the Bascom Palmer Eye Institute. He can be reached at Bascom Palmer Eye Institute, 900 NW 17th St, Miami, FL 33136; 305-326-6435; fax: 305-326-6474; e-mail: sgedde@med.miami.edu. Dr. Gedde has no direct financial interest in the products discussed in this article. A complete listing of investigators in the TVT Study Group is available at ajo.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.
- Joshi AB, Parrish R, Feuer WF. 2002 Survey of the American Glaucoma Society: Practice preferences for glaucoma surgery and antifibrotic use. J Glaucoma. 2005;14:172-174.