Evidence supports move to more use of drainage devices

By Laird Harrison

The weight of evidence from clinical trials over the past two decades supports the greater use of glaucoma drainage devices, said Kuldev Singh, MD, MPH.

Dr. Singh, professor of ophthalmology and director of the Glaucoma Service, Stanford University School of Medicine in California, described that evidence.

“When I was a resident in the 1980s, practitioners would commonly perform two or three trabeculectomy procedures before considering a tube implant,” said Dr. Singh. “But now, we are implanting tubes earlier, even as primary therapy in some cases.”

Watch as Kuldev Singh, MD, outlines how drainage devices in glaucoma are implemented.

Dr. Singh showed a slide of Medicare data in which trend lines for trabeculectomy rates had declined over the past two decades, while tube implantation rates were steadily rising with about a 10-fold increase in annual numbers over the past two decades.

One key trial was the Tube Versus Trabeculectomy Study (American Journal of Ophthalmology, 2012;153:789-803.)

In this study, 212 eyes that had undergone prior cataract surgery, trabeculectomy, or both procedures, were randomly assigned to either implantation with a 350-mm Baerveldt implant (Abbott Medical Optics) or a superior mitomycin C-augmented trabeculectomy.

Trabs had issues

After 5 years, the 2 groups achieved about the same average IOP, but the failure rate was higher in the trabeculectomy group. This was partly because hypotony, which was less common following tube implantation than trabeculectomy, was considered a failure.

“Even though both groups had about the same rates of failure due to inadequately high IOP, too low an IOP was a much bigger problem in the trabeculectomy group,” said Dr. Singh. “It’s rare that you get low single-digit IOPs in eyes that undergo long-tube drainage device implantation.”

The tube group required more medications initially, but after 3 years; this difference was not statistically significant between the 2 groups.

The reoperation rates were also higher in the trabeculectomy group, but rates of serious postoperative complications were similar. The most common serious postoperative complication in the tube group was diplopia, said Dr. Singh.

Common serious postoperative complications in the trabeculectomy group were related to overfiltration, sometimes due to wound leakage, he said. A greater rate of success in the tube group was noted regardless of the IOP cut-off for success.

”Whatever your IOP goal, tubes did better than trabs with no difference in glaucoma medications at 5 years in this study population,” said Dr. Singh.

The rate of complications for trabeculectomy in the TVT study, 37% at 1 month and 63% at 5 years, was comparable to the rates in other landmark glaucoma trials, such as the Collaborative Initial Glaucoma Treatment Study (CIGTS) and the Advanced Glaucoma Intervention Study (AGIS). Dr. Singh noted that most of these complications were transient and not considered serious or vision threatening.

Ahmed vs. Baerveldt

Dr. Singh reviewed two additional studies comparing the Baerveldt and Ahmed Valve (New World Medical) implants: The Ahmed Baerveldt Comparison Study (ABC) (Ophthalmology. 201;118:443-452) and the Ahmed Versus Baerveldt Study (AVB) (Ophthalmology. 2013;120:2232-2240).

Both compared the safety and efficacy of the Baerveldt 101-350 and the Ahmed FP-7 devices. “If you look around our glaucoma community, most practitioners have a preference for one of these two, but some commonly use both implants,” said Dr. Singh. Patients in the two studies, each of which recruited over 200 participants, had similar ages, IOP levels, glaucoma medication usage, and glaucoma diagnoses.

The Baerveldt group in each trial reached a lower mean IOP level than the Ahmed group, with the former group also showing a lesser dependence on postoperative IOP lowering medications.

The trade off was that Ahmed implantation was associated with fewer serious complications than Baerveldt implantation.

“Another difference is that with Baerveldt implantation, you don’t get the early IOP control that you get with the Ahmed device,” said Dr. Singh. “You need a ligature with a dissolving suture or some other method to obstruct flow and prevent hypotony in the early postoperative period with the Baerveldt, but not the Ahmed, as the latter has a flow-restriction mechanism.”

Patients implanted with Baerveldt devices commonly need intensive medical therapy, including oral carbonic anhydrase inhibitors, until the tube fully opens following dissolution of the ligating suture at about 4-6 weeks postoperatively, he said. Physicians get better early IOP control with the Ahmed and better long-term IOP control with Baerveldt.

“ The TVT, ABC, and AVT studies have provided data to support changing practice patterns,” said Dr. Singh. “We turn to tube implantation earlier for most glaucoma patients and consider these devices as primary therapy for certain high-risk circumstances, such as neovascular and uveitic glaucoma.

But he added that these studies only give results in terms of averages and therapy should be individualized. “You certainly want to look at patient-specific factors, including conjunctival status, disease severity, and IOP goal,” he said. “There are situations for which you hope to reach single-digit IOPs to adequately slow disease progression and trabeculectomy is more likely to get you there.”