Study results validate clinical trends showing increasing preference for tube surgery

September 1, 2008

Complications associated with trabeculectomy have prompted a search for better alternatives. Practice pattern data from recent years show growing usage of tube implants. Results of the multicenter, randomized Tube vs. Trabeculectomy study offer validation for this trend.

Key Points

Chicago-Results of the Tube Versus Trabeculectomy (TVT) study validate the belief that tube implants are a good alternative to trabeculectomy surgery. They may be fueling a recent trend for surgeons to perform tube procedures more often, at the expense of the number of trabeculectomies, said Herb Fechter, MD, at glaucoma day at the annual meeting of the American Society of Cataract and Refractive Surgery.

"These scenarios speak to the need to find a procedure that moves the filtering bleb away from the limbus and achieves more reliable pressure control with fewer complications and better patient comfort," said Dr. Fechter, assistant professor, Uniformed Services University of the Health Sciences, Bethesda, MD, and private practice, Augusta, GA.

The TVT study

The TVT study enrolled 212 patients with a history of previous ocular surgery (cataract extraction with IOL implantation and/or trabeculectomy) and an IOP between 18 and 40 mm Hg with tolerated medical therapy. Patients were randomly assigned 1:1 to undergo trabeculectomy with mitomycin-C or to receive a 350-mm2 glaucoma implant (Baerveldt, Advanced Medical Optics). The 1-year results for IOP outcomes and complications were first reported in March 2006 at the American Glaucoma Society (AGS) meeting and subsequently published in the Journal of Ophthalmology in January 2007.

At 1-year follow-up, mean IOP was similar in the patients who underwent nonvalved tube shunt surgery compared with the trabeculectomy group, 12.4 versus 12.7 mm Hg, respectively. However, patients in the tube group were more likely to maintain IOP control and avoid persistent hypotony and reoperation for glaucoma than the patients who underwent trabeculectomy, even though the patients with the tube implant on average needed more supplemental medical therapy than their counterparts who had filtering surgery, a mean of 1.3 versus 0.5 medications, respectively.

"Given the risks and complications of trabeculectomy, the need for additional medication after tube surgery may be worth it," Dr. Fechter commented.

More patients in the trabeculectomy group compared with the tube group experienced postoperative complications, 57% versus 34%, respectively. The difference is both statistically and clinically significant, Dr. Fechter said.

In particular, compared with tube surgery, trabeculectomy was associated with significantly more cases of wound leak (12 versus one), hyphema (eight versus two), and dysesthesia (seven versus one). However, persistent diplopia occurred only after tube surgery (five cases).

There were also trends for a higher overall rate of serious complications in the trabeculectomy group compared with the tube group (27% versus 17%) and for a higher rate of loss of 2 or more Snellen lines of vision (25% versus 15%).

Analyses of the cumulative probability of failure favored tube surgery regardless of the IOP cutoff. Considering a definition based on IOP >21 mm Hg, the cumulative probability of failure at 1 year was 13.5% in the trabeculectomy group and 3.9% among the tube group. The failure rates were 16.7% and 4.9%, respectively, based on an IOP >17 mm Hg and 27.4% and 11.9%, respectively, based on an IOP >14 mm Hg.

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