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.
The intraoperative stability of the anterior chamber is better than with trabeculectomy because no sclera is removed and therefore
there is no shallowing. There is also less chance of an intraoperative choroidal effusion or malignant glaucoma, said Dr Terri
Pickering, during last year's annual meeting of the American Academy of Ophthalmology (AAO).
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 Ám 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
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.