Tube versus Trabeculectomy Study: 3-year results

November 8, 2008

Three-year results from the Tube versus Trabeculectomy Study showed that tube-shunt surgery was more likely than trabeculectomy with mitomycin C to maintain IOP control and avoid persistent hypotony, loss of light perception vision, or re-operation for glaucoma. A highly significant difference between study arms was apparent in the cumulative probability of failure analysis, said Steven J. Gedde, MD, professor of ophthalmology, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine.

Three-year results from the Tube versus Trabeculectomy Study showed that tube-shunt surgery was more likely than trabeculectomy with mitomycin C to maintain IOP control and avoid persistent hypotony, loss of light perception vision, or re-operation for glaucoma. A highly significant difference between study arms was apparent in the cumulative probability of failure analysis, said Steven J. Gedde, MD, professor of ophthalmology, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine.

The cumulative probability of failure was estimated at 15.1% in the tube group and 30.7% in the trabeculectomy group at 3 years (p = 0.010, log rank test). Failure was prospectively defined as IOP above 21 mm Hg or not reduced by 20% below baseline on two consecutive visits after 3 months or IOP less than or equal to 5 mm Hg on two consecutive visits after 3 months. The 3-year analysis showed that most patients in both groups failed because of inadequate pressure control.

The treatment benefit for tube-shunt surgery was observed despite the findings of no significant difference between study groups in mean IOP and the mean number of glaucoma medications used at the 3-year time point. At baseline, the mean IOP in both groups was about 25 mm Hg, and the mean number of medications used was three. At 3 years, the mean IOP for both arms was about 13 mm Hg, while the number of medications was about one.

Visual acuity results in both study groups showed a reduction over the 3-year period, and Snellen and Early-Treatment Diabetic Retinopathy Study acuity were similar for both sets of patients.

Although the findings do not demonstrate clear superiority of one glaucoma operation over the other, they suggest that the role of tube shunts should be expanded, Dr. Gedde said. Tube shunts have traditionally been reserved for refractory glaucoma at high risk of failure with trabeculectomy, although their use has begun to grow recently to encompass less refractory cases.

The study enrolled 212 eyes of 212 patients at 17 clinical centers in the United States and Great Britain. The tube group (n = 107) and the trabeculectomy group (n = 105) were very evenly matched at baseline.