Stability a strength of filtration device

January 1, 2011

A glaucoma filtration device has several advantages that compare favorably with trabeculectomy.

Chicago-A glaucoma filtration device (Ex-PRESS, Alcon Laboratories) has several advantages-such as greater stability during and after surgery-that compare favorably with trabeculectomy, according to a surgeon who has performed a number of procedures using this technique.

The intraoperative stability of the anterior chamber is better than with trabeculectomy since no sclera is removed and therefore there is no shallowing. There also is less chance of an intraoperative choroidal effusion or malignant glaucoma, said Terri Pickering, MD, at the annual meeting of the American Academy of Ophthalmology (AAO).

Stability also is enhanced postoperatively because of the design of this device, which is not valved. It has a constant, controlled internal lumen of 50 µm that provides a degree of resistance to aqueous outflow as well as a greater measure of control over hypotony, Dr. Pickering explained, adding that the chamber tends to stay deeper even at low pressures.

Overall, the results tend to be more stable and more predictable than when performing trabeculectomy.

"It's trying in a way to accomplish the ultimate goal, which is making glaucoma filtering surgery more of a standardized procedure," said Dr. Pickering, who is in practice at the Glaucoma Center of San Francisco. "It hasn't completely achieved that goal, but it's a step in that direction."

She also mentioned that since implantation of the filtration device is a refinement of trabeculectomy, which is an established technique, the learning curve is short.

"You already know how to do it. You're just adding one step and taking away two others," Dr. Pickering explained.

A further advance of the shunt is that it reduces inflammation because implantation under the sclera does not require iridectomy or sclerectomy. The risk of inflammation is also lower because tissue is not removed and there is less chance of hyphema or pigment release.

The shunt was invented in 1996 by Ira Yaron, chief executive officer of Optonol, which was subsequently acquired by Alcon. The device received FDA approval in 2002. It was originally designed to be implanted under the conjunctiva, but a technique to implant it under the scleral flap was introduced in 2003.

Although not a new device, some glaucoma surgeons remain reluctant to use it or skeptical of claims of its advantages, Dr. Pickering said. She suggested that in many cases physicians simply have preferred practice patterns that would be disrupted by adopting the shunt technique, while others are concerned about the additional cost of using this drainage device as opposed to performing a straightforward trabeculectomy. Other physicians have suggested the need for more data; although small studies of this drainage device have been performed, there has not been a large, randomized, controlled trial.

Establishing a niche

Dr. Pickering agreed that more data are needed to secure the device's position in the glaucoma management algorithm but suggested that it is a promising device that has established a niche. More than 45,000 of the shunts have been implanted worldwide.

In a booth presentation at the AAO, Dr. Pickering discussed some unusual cases in which she felt this drainage device made a difference.

"It's not a substitute for one of the classic, large-plate glaucoma shunt implants like the Ahmed or the Baerveldt or the Molteno. It's positioned more toward the end of trabeculectomy," she said. "However, having said that, there are a few cases where it can be a preferred device over trabeculectomy or one of the glaucoma tube shunts simply because it's made of stainless steel and it's very small."

Favorable applications

In cases where there are corneal issues, the device might be preferable to trabeculectomy or a flexible plastic tube shunt because the small, stiff drainage device would not bump against the cornea if the patient rubbed the eye. Or, if a patient was scheduled for corneal surgery, the inflammation associated with this procedure might lessen the effectiveness of a subsequent trabeculectomy.

Another instance in which the drainage device might be useful would be cases involving monocular patients. These patients need the best possible outcomes-less inflammation, more rapid recovery, and more stability of the eye postoperatively-and for them the device could be beneficial.

"It's not for every glaucoma situation. Some people will need the larger plate tube shunts, and some people won't be able to have [the] glaucoma device because their angle may be too narrow or they have a lot of peripheral anterior synechiae," Dr. Pickering concluded. "Just like any other surgery, you have to pick the best procedure for the patient and the situation."

fyiTerri Pickering, MD
Phone: 415/981-2020
Dr. Pickering is a consultant to Alcon Laboratories and Allergan.
http://www.glaucomasf.com/