A multicenter, randomized clinical trial comparing the efficacy of the Ahmed valve implant with the B?rveldt implant for treating refractory glaucoma found that 1 year after surgery, the IOP, number of glaucoma medications, and rate of failure were lower in patients who received the B?rveldt implant.
However, patients who received the Baerveldt implant experienced a greater number of IOP spikes and required more postoperative interventions to achieve these results. The visual acuity (VA) outcomes achieved with the two devices were similar.
The Ahmed valve implant and the Baerveldt implant are the two most frequently selected aqueous drainage devices used by surgeons to treat glaucoma that is refractory to medical, laser, and other surgical therapy.
The Baerveldt implant does not have a valve mechanism and requires early flow restriction to allow adequate time for a mature bleb to form. This can result in a period of high IOP immediately postoperatively but may have the advantages of less encapsulation, lower IOPs, and the need for fewer glaucoma medications in the long term. However, because there is no built-in flow-restrictor and the Baerveldt device has a larger filtering surface area than the Ahmed valve (350 mm2 versus 184 mm2), there may be a greater risk of hypotony-related complications.
Ike Ahmed, MD, assistant professor at the University of Toronto Department of Ophthalmology & Vision Sciences, and colleagues conducted the AVB (Ahmed versus Baerveldt) Study, an international, seven-site, randomized clinical trial to compare the Ahmed-FP7 valve implant with the Baerveldt-350 implant for treating patients with glaucoma refractory to maximum medical, laser, and conventional surgical treatment. These findings were presented at the annual meeting of the Association for Research in Vision and Ophthalmology by lead author Panos G. Christakis, BSc.
All previous studies comparing these two devices have been retrospective, nonrandomized, and compared different models, yielding inconclusive results. Patients were recruited by 10 surgeons, who performed the procedures between October 2005 and January 2009.
The two treatment arms were similar in baseline demographic and ocular parameters. The mean baseline IOP of the study group was 31.4 ± 10.8 mm Hg, the median Snellen VA was 20/100, the mean logarithm of the minimum angle of resolution (logMAR) VA was 1.2 ± 1.0, the mean number of previous laser therapies was 0.9 ± 1.1, the mean number of previous surgeries was 1.7 ± 1.2, and the mean number of glaucoma medications before surgery was 3.1 ± 1.0.
Patients were followed after surgery at 1 day, 1 and 2 weeks, and 1, 2, 3, 6, 12, and 18 months, and visits were planned for 2, 3, 4, and 5 years postoperatively. At each visit, the IOP, best-corrected Snellen VA, number of glaucoma medications, and any complications or interventions required were recorded. The study group established an IOP target of 5 to 18 mm Hg inclusive with a reduction of at least 20% from baseline. Surgical failure was defined as two consecutive visits at or after 3 months in which the IOP target was not met, the need for additional glaucoma surgery, the development of devastating complications, or deterioration of VA to no light perception.