Performance compares favourably with trabeculectomy, in physician's experience
A glaucoma filtration device (Ex-PRESS, Alcon Laboratories) has several advantages - such as greater stability during and after surgery - that compare favourably with trabeculectomy, according to a surgeon who has performed a number of procedures using this technique.
Stability is also 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 because 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.