Aqueous Shunts for the Treatment of Glaucoma

Jeffrey A. Tice, MD



In This Article


Glaucoma is the second leading cause of blindness worldwide after cataracts. The pathophysiology of glaucoma remains incompletely understood, but lowering IOP has been demonstrated to slow the progressive loss of peripheral and central vision that are the hallmarks of the disease. Medical therapy and laser therapy for glaucoma have improved over the past thirty years, but a substantial portion of patients with glaucoma continue to progress in spite of maximally tolerated non-invasive therapy. Surgical trabeculectomy has been the established therapy for this group. However, trabeculectomy carries with it short term risks for worsening vision or blindness, long term risks for ocular infections, and a tendency to fail over time, particularly for patients with glaucoma associated with neovascular disease, uveititis, or iridocorneal endothelial disease.

Aqueous shunts were developed as an alternative to trabeculectomy. Initially, they were used for patients who had failed trabeculectomy and for patients with diseases known to have a poor outcome with trabeculectomy. A large number of randomized trials evaluating aqueous shunts have been published, but many were small and focused on technical aspects of the surgery. Early trials established that larger endplates lead to better IOP control, but that very large endplates increase the risk for complications without additional clinical benefits. Two recent trials have had the largest impact on clinical practice and are the most important to focus on when deciding whether aqueous shunts meet CTAF's TA criteria. The Tube versus Trabeculectomy study was a multicenter trial that randomized 212 patients who had undergone prior ocular surgery to either the Baerveldt 350 mm2 shunt or surgical trabeculectomy. Through three years of follow-up the two procedures had similar rates of IOP control, vision loss, cataract progression, and reoperations. However, patients in the Baerveldt tube group had a lower rate of complications and a lower failure rate. This study demonstrated that net outcomes with the Baerveldt aqueous shunt were at least equivalent to those achieved by trabeculectomy in patients who had undergone prior surgery.

The ABC study randomized 286 patients to one of two popular aqueous shunts, the Ahmed and the Baerveldt 350 mm2. Through one year of follow-up outcomes were similar in the two groups, though there was a trend towards fewer complications in the Ahmed group and better IOP control in the Baerveldt group. Although the overall outcomes are similar to date, the relative mix of benefits and harms may guide a surgeon in choosing one device over another. Additional results from this study extending the results from one year out to five years of follow-up will be forthcoming.

The data supporting the Ex-PRESS shunt are less robust. There are two small randomized trials comparing the device to trabeculectomy. Both were single surgeon studies and one involved only 30 eyes in 15 patients. The results suggest that the Ex-PRESS shunt has similar success rates as trabeculectomy, but lower rates of complications. This literature would benefit from a large trial comparing the Ex-PRESS shunt to one of the aqueous shunts that has been well studied, like the Baerveldt 350.