Mini-glaucoma shunt rivals trabeculectomy, results indicate

Key Points

Trabeculectomy has long been and still is the gold standard as surgical treatment of medically uncontrolled glaucoma disease. The shunt, however, clearly rivals the widely used trabeculectomy approach by proving to be at least as effective in controlling IOP with significantly less postoperative adverse events, Dr. Netland said. He is professor of the Department of Ophthalmology at the University of Tennessee Health Science Center, Hamilton Eye Institute, Memphis.

The implantation technique of the mini-shunt has been modified-the stainless steel device now is placed under a scleral flap. It provides a way of producing a glaucoma-filtering procedure that is even safer than that achieved through trabeculectomy, he said. Several variations of the shunt are available, all of which have a 400-µm external diameter, allowing the device to be placed via a 25- to 27-gauge needle tract, and range from a 50- to 200-µm internal diameter. According to Dr. Netland, most clinicians use the 50-µm internal diameter device.

According to Dr. Netland, the first few weeks after surgery is the period that often is problematic for surgeons because patients can develop hypotony as well as complications related to it, such as shallow or flat anterior chamber, choroidal effusions, and suprachoroidal hemorrhages.

The implant procedure resembles a trabeculectomy in that it has a scleral flap, but it is not a trabeculectomy in the sense that no excision of trabecular tissue is made and no iridectomy or sclerotomy is performed. The opening produced in the implant procedure is a set standard size, 50 µm, and is reproducible in all procedures, which is one of the major advantages of the technique, he said.

"This standardization reduces the chance of surgeon-generated error in variations in procedure, unlike in sclerostomy procedures where we see a lot more variability in opening size," Dr. Netland said. "The internal diameter of the device where the aqueous flows out of the eye is always the same and does not vary from procedure to procedure. Also, we see significantly reduced tissue trauma and inflammation in the postoperative period compared [with] trabeculectomy."

This all adds up to more predictable results and fewer complications, particularly less hypotony and complications related to it, he said. Also, the procedure is much faster than standard trabeculectomy due to fewer surgical steps as well as the standardized and reproducible technique.

Studies performed

Dr. Netland and colleagues performed a retrospective study in which the mini-glaucoma shunt was compared with standard trabeculectomy. In the study, 100 eyes were retrospectively compared that had been treated with the shunt or standard trabeculectomy. Results showed that IOP control of the shunt under a scleral flap was equally as effective when compared with trabeculectomy.

"Long-term pressure control and long-term success rates were similar, but in the early postoperative period, we found a lower rate of hypotony and the sequelae of hypotony with the [shunt]," he said. "These results are significant because the gold standard trabeculectomy procedure was successfully challenged."

In a more recent study including 345 eyes, Dr. Netland compared the implant alone with the implant used in combination with cataract surgery. The results similarly showed IOP control in both study arms.

He said that it was interesting, however, that the number of medications and the IOPs were slightly lower at a few time points during follow-up in the patients who received the implant alone compared with those who additionally underwent cataract surgery.

This similar scenario is seen in patients who undergo combined trabeculectomy and cataract surgery in terms of achieving a slightly better pressure control without adjunctive cataract surgery, Dr. Netland added. One of the advantages of the study was the insight gained on long-term complications, because relatively uncommon complications were apparent in this series that were not apparent in previous smaller series.

Blocked tube

The most common device-related complication was blocked tube, which occurred in 1% to 2% of the patients (six of 345 patients).

"Blocked tube occurs when a fine inflammatory material collects inside the tube," he said. "This was actually very difficult to see, but we could make the diagnosis when we found that patients had an elevated pressure and a low bleb following the procedure."

In response, Dr. Netland treated the blocked tube with an Nd:YAG laser at low power (1 to 2 mJ) and found that this quickly and successfully opened the tube in all of those patients. The blocked tube was a device-related complication; however, it was not serious and it was easily managed with the laser, proving that the device works well in a large series of patients without major complications.

"The [device] is most useful for primary glaucoma surgery," he said. "We feel that it probably is not as well suited for refractory glaucoma [surgeries] that are refractory to other surgeries, although it can certainly be used for this purpose in select cases."

The implant procedure may not be ideal in patients with chronic inflammation due to the potential blockage of the tube.

Although complications appear to be uncommon with the device and it seems to have a good biocompatibility, Dr. Netland said that it may be better to avoid using this shunt in younger patients until the long-term biocompatibility follow-up on these patients becomes available.