Miniature glaucoma shunt comparable to trabeculectomy

January 15, 2006

Chicago—Similar IOP-lowering outcomes were attained in eyes that underwent trabeculectomy or received the Ex-PRESS miniature glaucoma shunt (Optonol) placed under a partial-thickness scleral flap. Hypotony was less frequent in eyes that received the implant, according to the results of a comparison study.

"There was no statistically significant difference in success or in the IOPs in the long term after either procedure. We conclude from this that the Ex-PRESS implant had a similar IOP-lowering efficacy when compared with trabeculectomy, but it had a lower rate of early hypotony than trabeculectomy," said one of the investigators, Peter Andreas Netland, MD, PhD, Siegal professor of ophthalmology, University of Tennessee Health Science Center, Memphis.

He and colleagues conducted a comparative case-control series of 50 eyes that received the Ex-PRESS implant and 50 that underwent trabeculectomy. The patients were matched by age, gender, race, and diagnosis.

"During the early postoperative period there was less hypotony in the group that had had the Ex-PRESS implant and there were also fewer complications associated with hypotony. We found fewer choroidal effusions and fewer shallow anterior chambers in patients who had had the Ex-PRESS implant underneath the flap as compared with other patients who had had standard trabeculectomy," Dr. Netland said.

Early postoperative hypotony occurred in 6% of the eyes with the Ex-PRESS shunt implanted and 34% of eyes that had undergone trabeculectomy.

Because a number of problems are associated with trabeculectomy, clinicians want to find ways to improve their results after filtration surgery; this implant is one of the other options, Dr. Netland said. The implant was originally designed for placement under the conjunctiva and could be implanted in the office using a slit lamp. Initial results, however, were not entirely satisfactory; some patients developed hypotony in the early postoperative period, and others developed complications later, such as erosion of the conjunctiva.

Implant under scleral flap

To avoid these issues, some clinicians have begun using the implant under a scleral flap, much like trabeculectomy, and the study was designed to compare this approach with standard trabeculectomy.

"I view this as an adjunctive technique that can potentially improve the results that we're getting with trabeculectomy," Dr. Netland said. "The use of the Ex-PRESS implant isn't really an alternative choice to glaucoma drainage implants. It's more of an alternative approach to trabeculectomy.

"The advantages of the Ex-PRESS implant are that it definitely does involve less surgical time and less trauma to tissues," he continued. "No tissue is removed; sclerostomy or peripheral iridectomy is not part of this procedure. You simply place the implant underneath the flap through a needle track. It's a straightforward procedure that is efficient and causes less tissue trauma.

"Also, because the procedure is standardized, it has very predictable results. We found in our comparative trial that there are fewer complications as well. We're more efficient intraoperatively and have a smoother course postoperatively," he said.

The disadvantages are that the device costs money to implant and raises compatibility issues. In animal studies, however, compatibility has been found to be excellent, and no compatibility problems were observed in the clinical trial, Dr. Netland said.

"It's a useful device for guarded filtration surgery. It could be used for straight filtration surgery or combined with cataract surgery," he noted.

There are not yet any criteria for deciding when the implant should be used, and nearly any patient who is a candidate for trabeculectomy would also be a candidate for the Ex-PRESS implant, Dr. Netland said. Lacking any specific criteria, he currently avoids implanting the device in younger patients because its long-term effects are unknown.