Do drainage devices implanted into the eye improve glaucoma surgery's outcomes compared to trabeculectomy, the current gold standard in filtration procedures? That depends on the type of glaucoma and patient being treated. Tube vs. trabeculectomy research seems to indicate that tube shunt surgery represents a viable option when compared to standard filtration surgery.

Aqueous escape route
Here's a simple way to think of glaucoma shunts and stents: Surgeons insert them into the anterior chamber during a trabeculectomy to increase outflow of intraocular fluid and reduce high eye pressure. The devices create an alternative route for the aqueous to escape from the eye, dodging the damaged or backed-up drainage system canal.

Implanting drainage devices is a more complex procedure than conventional trabeculectomy — efficient surgeons can perform the task in as little as 30 minutes, but close to 45 minutes is more the norm — and complications can develop, including double vision, tube erosion or plugging, implant failure and corneal failure.

The valved Ahmed and Baerveldt tube shunts are the most widely used and best suited to treat severe or chronic forms of glaucoma. Surgeons can also reduce intraocular pressure by using Alcon's Express glaucoma filtration device, a small (less than 3mm) stainless steel implant that diverts fluid from the anterior chamber to the subscleral space. Patients ideally suited for this device present with moderate to severe uncontrolled open-angle glaucoma that previous medical and surgical interventions failed to treat. On the other hand, patients with angle-closure glaucoma, uveitis, severe dry eye and blepharitis may not be ideal candidates for implantation.

The device should be inserted under a scleral flap, avoiding the need for an iridectomy. It has, in a way, standardized trabeculectomy outcomes by making results more consistent and predictable. Its use also results in fewer potential intra- and post-op complications — including hyphema and inflammation that decreases visual acuity — compared to conventional trabeculectomy. I've found that patients implanted with this device recover about 2 weeks faster than they do following standard filtration surgery.

Other new devices that could improve the outcomes of filtration surgery are currently in FDA clinical trials and might soon gain approval for commercial release. One of those implants, the iStent from Glaukos, is a snorkel-like device that's inserted into Schlemm's canal in patients with open-angle glaucoma caused by trabecular meshwork abnormalities. The implant redirects aqueous fluid around the abnormal trabecular meshwork to channels in Schlemm's canal, thereby eliminating fluid blockage and establishing normal flow.

First option or last resort?
Implant surgery and standard trabeculectomy are comparable options for reducing intraocular pressure. In my practice, tube shunt surgery is most often performed in patients with advanced glaucoma and commonly after when traditional filtration surgery fails. However, tube shunt surgery can be reasonably offered as a first-line surgical treatment in certain situations. Whatever devices or techniques surgeons use, glaucoma surgery should be safe, easy and effective at reducing intraocular pressure, as well as repeatable.