The Tube Vs. Trabeculectomy Study: What 5-Year Results Teach Us

Long-term outcomes show trabeculectomy and tube shunt surgery are both viable for managing glaucoma in eyes with previous ocular surgery.

Steven J. Gedde, MD, Dale K. Heuer, MD, Richard K. Parrish II, MD, and The Tube Versus Trabeculectomy Study Group

Glaucoma surgery is indicated when medical therapy and appropriate laser treatment do not provide adequate IOP reduction to prevent progressive optic nerve damage. Despite the introduction of several new incisional glaucoma procedures in recent years, trabeculectomy (or guarded filtration procedure) and tube shunt (or aqueous shunt) surgery remain the most frequently performed glaucoma operations worldwide.

Numerous case series have described the outcomes of these two procedures, but few studies have directly compared tube shunts to trabeculectomy. The Tube Versus Trabeculectomy (TVT) Study is a multicenter randomized clinical trial designed to compare the safety and efficacy of tube shunt surgery and trabeculectomy with mitomycin C (MMC) in eyes with previous ocular surgery.

The TVT Study offers a wealth of information that further defines the relative risks and benefits of trabeculectomy with MMC and tube shunt surgery in a specific patient population. However, the study does not demonstrate clear superiority of one glaucoma operation over the other. Many factors must be considered when selecting a surgical procedure, including the surgeon's skill and experience with both operations and the individual patient's characteristics. Surgeons should analyze and interpret the TVT Study data critically, and then draw appropriate conclusions to help them in selecting the optimal glaucoma operation for individual patients.

This article offers a closer look at the TVT Study with the goal of helping surgeons interpret the data and apply it in clinical practice.

Study Population

The TVT Study enrolled a total of 212 eyes of 212 patients at 17 clinical centers, including 107 in the tube group and 105 in the trabeculectomy group.¹ The mean age of the study population was 71 years, and 53% were women. Baseline IOP was 25.3 ± 5.3 mm Hg (mean ± SD), and 81% of patients had primary open-angle glaucoma.

Among enrolled patients, 44% had undergone cataract surgery, 35% trabeculectomy and 20% combined cataract and glaucoma surgery as the qualifying previous ocular surgery for the study. No significant differences in any of the demographic and ocular characteristics were observed between the tube and trabeculectomy groups. This suggested that randomization was effective in creating two balanced treatment groups.

Figure: Kaplan-Meier Curves of the Probability of Failure In The Tube Versus Trabeculectomy Study

IOP and Medical Therapy

The trabeculectomy group had significantly lower mean IOPs than the tube group at all follow-up visits during the first three months, but no significant difference in the degree of IOP reduction persisted between treatment groups after three months (TABLE).^{2, 3} The use of supplemental medical therapy was significantly greater in the tube group during the first two postoperative years. However, the need for glaucoma medications progressively increased in the trabeculectomy group and remained stable in the tube group such that the mean number of medications did not differ between treatment groups at three years and thereafter.³

Surgical Success

The cumulative probability of failure was 29.8% in the tube group and 46.9% in the trabeculectomy group at five years (p = 0.002; HR = 2.15; 95% CI = 1.30–3.56) (FIGURE).³ However, no significant difference in the distribution of reasons for treatment failure was evident between treatment groups (p = 0.43). The five-year cumulative reoperation rate for glaucoma with Kaplan-Meier survival analysis was 9% in the tube group and 29% in the trabeculectomy group (p = 0.025).

The TVT Study performed several post-hoc analyses with alternative outcome criteria to determine whether results changed if more stringent IOP criteria were applied to define success and failure.³ The trabeculectomy group had significantly higher failure rates than the tube group when the upper IOP level defining success was 17 mm Hg (31.8% tube group vs. 53.6% trabeculectomy group; p = 0.002; HR = 2.04; 95% CI = 1.29–3.24) and 14 mm Hg (52.3% tube group vs. 71.5% trabeculectomy group; p = 0.017; HR = 1.57; 95% CI = 1.09–2.26). Because the difference in treatment outcomes was evident with a broad range of IOP success criterion, the study results seem applicable to patients with early or advanced glaucomatous damage.

Surgical Complications

Despite a substantial number of surgical complications in the TVT Study, most were transient and self-limited.⁴ Significantly more patients in the trabeculectomy group (63%) experienced postoperative complications compared with the tube group (43%) during five years of follow-up (p = 0.006).

All complications are not equal in severity. The frequency of serious complications requiring a reoperation to manage the complication or producing loss of 2 or more lines of Snellen visual acuity (VA), or both, was similar between the tube group (22%) and trabeculectomy group (20%) at five years (p = 0.79).

Visual Acuity

Reduction in VA was observed in both the tube and trabeculectomy groups during five years of follow-up, and Snellen and ETDRS VA were similar between treatment groups at baseline and at five years.³ The rate of loss of 2 or more lines of Snellen VA was not significantly different between the tube group (46%) and the trabeculectomy group (43%) after five years (p = 0.93). Many of the causes of vision loss in both treatment groups, such as macular degeneration and diabetic retinopathy, were not directly attributable to the surgical procedures under study.

Impact on Clinical Practice

The TVT Study has supported a major shift in glaucoma surgical practice patterns, which was already under way before its results were published. Recent surveys of the American Glaucoma Society have shown a rise in the popularity of tube shunts and a decline in the proportion of surgeons who routinely select trabeculectomy to manage medically uncontrolled glaucoma.^5–7 The greatest relative increase in the use of tube shunts was observed in the patient groups investigated in the TVT Study — those who had previous cataract surgery and failed trabeculectomy. Medicare claims data also demonstrated a 43% decrease in the number of trabeculectomy procedures and a concurrent 184% increase in tube shunt surgery between 1995 and 2004.⁸

The TVT Study supports the expanded use of tube shunts beyond the surgical management of refractory glaucoma. Tube shunt surgery was shown to be effective in a patient population at lower risk of surgical failure than has traditionally been relegated to this procedure.

The study results have prompted another multicenter randomized clinical trial, the Primary Tube Versus Trabeculectomy Study, comparing tube shunt surgery and trabeculectomy with MMC as an initial surgical procedure in low-risk eyes. This represents a different patient population than that evaluated in the TVT Study. The TVT Study also demonstrated that low levels of IOP could be achieved with tube shunts in this patient group, challenging conventional wisdom about the efficacy of tube shunt implantation. OM

References

1. 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.
2. 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.
3. Gedde SJ, Schiffman JC, Feuer WJ, et al. Treatment outcomes in the Tube Versus Trabeculectomy Study after five years of follow-up. Am J Ophthalmol. 2012;153:789–803.
4. Gedde SJ, Herndon LW, Brandt JD, et al. Postoperative complications in the Tube Versus Trabeculectomy Study (TVT) during five years of follow-up. Am J Ophthalmol. 2012;153:804–814.
5. 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.
6. Joshi AB, Parrish RK, Feuer WF. 2002 Survey of the American Glaucoma Society. Practice preferences for glaucoma surgery and antifibrotic use. J Glaucoma. 2005;14:172–174.
7. Desai MA, Gedde SJ, Feuer WJ, et al. Practice preferences for glaucoma surgery: A survey of the American Glaucoma Society in 2008. Ophthalmic Surg Lasers Imaging. 2011;42:202–208.
8. Ramulu PY, Corcoran KJ, Corcoran SL, Robin AL. Utilization of various glaucoma surgeries and procedures in Medicare beneficiaries from 1995 to 2004. Ophthalmology. 2007;114:2265–2270.

Drs. Gedde, Heuer and Parrish are the study chairmen for the TVT Study, which was supported by research grants from Pfizer, Abbott Medical Optics, the National Eye Institute, and Research to Prevent Blindness. Drs. Gedde and Parrish are with the Bascom Palmer Eye Institute, University of Miami, Miller School of Medicine. Dr. Heuer is with the Department of Ophthalmology, Medical College of Wisconsin, Milwaukee.