Tube Shunts Better for Second Surgery in Glaucoma Patients

April 26, 2012 — Tube shunt surgery for glaucoma patients who had already undergone eye surgery was less likely to fail than trabeculectomy in a 5-year, 212-patient trial conducted at 17 clinical centers, a study published in the May issue of the American Journal of Ophthalmology shows.

Steven J. Gedde, MD, professor of ophthalmology, Bascom Palmer Eye Institute, Miller School of Medicine, University of Miami, Florida, and colleagues randomly assigned 212 patients to receive a 350-mm² Baerveldt tube shunt implant (n = 107) or undergo trabeculectomy with mitomycin C (MMC; n = 105) to relieve intraocular pressure in glaucoma. The research took place from 1999 to 2004.

The researchers found that intraocular pressure (IOP) 5 years after the procedure was essentially the same for both groups (14.4 ± 6.9 mmHg in the tube group vs 12.6 ± 5.9 mmHg in the trabeculectomy group; P = .12), as were the number of glaucoma medications patients required after surgery (1.4 ± 1.3 vs 1.2 ± 1.5, respectively; P = .23). However, the surgical failure rate in the trabeculectomy plus MMC group was greater. Among trabeculectomy patients, 29% required another surgical procedure for glaucoma, compared with 9% of patients in the tube group (P = .025). The cumulative probability of failure during the 5-year follow-up was 29.8% in the tube group and 46.9% in the trabeculectomy group (hazard ratio [HR], 2.15; 95% confidence interval [CI], 1.30 - 3.56; P = .002).

Failure was defined as an IOP greater than 21 mmHg or less than 20% reduction below baseline on 2 consecutive follow-up visits after 3 months, an IOP of 5 mmHg or less on 2 consecutive follow-up visits after 3 months, reoperation for glaucoma, or loss of light perception vision.

Trabeculectomy Failure Rate Is Shockingly High

"Based on the definitions of success that were set up prior to the clinical trial, tubes came out overall to have a higher success rate," James D. Brandt, MD, professor of ophthalmology and director of Glaucoma Services, University of California, Davis, Sacramento, a study coauthor, told Medscape Medical News. "Most people, if they did an honest chart review of trabeculectomies, would be shocked at the failure rate. It's a good operation. It's not a great operation. The really long-term results show trabeculectomies are not quite as good as we thought they were and tubes might be a lot better."

A second study by the same research group, also in the May issue of the American Journal of Ophthalmology, showed that late postoperative complications, reoperations, and cataract extractions were similar for both surgeries, although trabeculectomy was associated with a higher rate of early postoperative complications than tube implantation.

Early postoperative complications occurred in 22 (21%) of the patients in the tube group and 39 (37%) of those in the trabeculectomy group (P = .012). Late complications developed in 36 (34%) of the tube group and 38 (36%) of the trabeculectomy group (P = .81). Another operation to resolve complications was necessary in 22% of the tube group and 18% of the trabeculectomy group; the difference between the groups was not statistically significant (P = .29). Incidence of serious complications leading to another operation or vision loss was similar in the groups: 24 patients (22%) in the tube group and 21 patients (20%) in the trabeculectomy group (P = .79). Cataract extractions were performed in 13 phakic eyes (54%) in the tube group and 9 phakic eyes (43%) in the other cohort.

These papers mark the third and final analysis of the Tube Versus Trabeculectomy (TVT) study. The group also published year 1 results and year 3 results.

"I think it's a very important study, and, for a lot of us, a little bit surprising but actually encouraging that the drainage tube implants work pretty well," Joern B. Soltau, MD, associate professor, Department of Ophthalmology and Visual Sciences, University of Louisville, Kentucky, told Medscape Medical News.. "They have side effects and complications, but overall they're a good alternative. You have to still look at each patient individually. The study provides some guidance, but it's not a rule book." Dr. Soltau was not involved in the study.

Yet the definition of what constitutes a failure for the purposes of this study raised questions for some.

Both Trabeculectomy and Tube Implants Are Viable Options

"It's a very well-designed study that is providing a lot of important information, but it's not going to cause any sudden shifts in people's practice patterns," Arthur Sit, MD, associate professor of ophthalmology and a consultant in ophthalmology at the Mayo Clinic, Rochester, Minnesota, told Medscape Medical News. "My interpretation is, they're actually both still viable options." Dr. Sit was not involved in the study.

Despite his praise for the study, he called the inclusion of hypotony as a sign of procedure failure, with no accompanying criteria for loss of visual acuity, "too broad."

"This issue of counting hypotony as failure is something that's been discussed since they presented 1-year results," Dr. Sit said. He said an analysis included in the current publications, which recalculates the failure rate by moving the 3 patients with hypotony with no vision change out of the failure category, doesn't adequately deal with the problem, considering that both surgical cohorts had significant vision loss.

"If the entire group has decreased vision over time, then removing just the patients who have completely unchanged vision and hypotony is not sufficient. There needs to be a better definition of what is an acceptable rate of vision loss," Sit said. "The post hoc analysis really doesn't address the issue fully, so the potential criticism still exists that they're counting patients who have hypotony but insignificant change in vision as a failure."

At least 1 of the study authors says he understands the objections. "I agree with that criticism of the study, and I was one who said we should qualify failure on the low pressure side in terms of vision change," said Dr. Brandt. But even with such a change in failure standards, "We probably wouldn't have had quite as many failures (in the trabeculectomy group) but I'm not convinced it would have made a big difference in the outcome of the study."

"We spent a lot of time talking about this. It's pretty straightforward to define success and failure based on pressure at the high end. It's hard to figure out what constitutes a failure on the low end."

Hypotony Debate Is "Petty" and "Unfounded," States Expert

Donald L. Budenz, MD, MPH, professor and chair, Department of Ophthalmology, University of North Carolina, Chapel Hill, told Medscape Medical News that the debate over the inclusion of hypotony as a sign of failure is a "petty objection" and "unfounded." He notes that the TVT study definition of failure is taken from guidelines established by the World Glaucoma Association. "It's not like we have a different criteria than everyone else. There's actually consensus on the issue and it includes exactly what we use as success and failure." Dr. Budenz was one of the coauthors of the study.

An editorial by Ronald L. Gross, MD, professor of ophthalmology, Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, that accompanies the 2 studies cautioned that changes in trabeculectomy technique during the course of the study may have affected study results. For instance, the amount of MMC used in the study population — at 0.4 mg/mL for 4 minutes — is high by current standards. "Lower doses and less duration as well as a larger area of MMC application are current practice to limit the risk of hypotony and bleb leaks," he writes.

In addition, Dr. Gross writes that surgical interventions may be overestimated by the inclusion of suture lysis, 5-fluorouacil injections, and removal of ripcords among the interventions. "Generally, these should be considered an expected part of the procedure, and although they occasionally result in complications, those would be identified separately."

When Trabeculectomy Fails, Turn to Tube Implants

The results of the TVT study are already having an effect, Dr. Budenz said.

"It really lends credence to a new treatment algorithm, that once a trabeculectomy fails, we should go to the tube implant. I think it definitely has changed clinical practice significantly in terms of more frequent use of tube implants," he said.

Surgeons have been increasingly turning to tube shunts, also called aqueous shunts, as a way to relieve IOP, the authors write. Medicare claims for tube shunting increased 184% between 1995 and 2004, while claims for trabeculectomy fell 43%.

The study authors caution that the results cannot be generalized to other surgical situations for glaucoma, such as using tube implants as the first procedure in response to elevated IOP. The authors are addressing that question in a new study for which they are currently recruiting patients.

The studies were supported by research grants from Pfizer Inc; Abbott Medical Optics; the National Eye Institute, National Institutes of Health; and Research to Prevent Blindness Inc. Dr. Brandt and other study authors disclosed financial interest in the manufacturer of the Baerveldt glaucoma implant. Dr. Gross is a consultant for Alcon and Allergan and has received lecture fees from Allergan and Merck, and his institution has received grants from Alcon and Allergan. Dr. Sit has consulted for Alcon and Allergan, as well as Glaukoes. Dr. Soltau has disclosed no relevant financial relationships.

Am J Ophthalmol. 2012;153:789-803, 804-814. Outcomes study abstract Complications study abstract Editorial