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Editors Selection IGR 21-4

Surgical Treatment: Drainage devices

Comment by Robert Feldman on:

53960 The Ahmed Versus Baerveldt Study: Three-Year Treatment Outcomes, Christakis PG; Tsai JC; Kalenak JW et al., Ophthalmology, 2013; 120: 2232-2240

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The use of glaucoma drainage devices to treat glaucoma is increasing. Choice of shunt is a matter of surgeon preference; there are no clear guidelines for choosing a particular shunt. The Ahmed Versus Baerveldt (AVB) study is a multi-center, randomized trial that compares the Ahmed FP7 Glaucoma Valve (New World Medical, Santa Ana, CA) and the Baerveldt-350 Glaucoma Implant (Abbott Medical Optics, Inc., Rancho Cucamonga, CA).

This paper compares the three-year treatment outcomes of these two implants in patients with refractory glaucoma. A total of 238 patients were enrolled; 124 were randomized to receive the Ahmed implant, and 114 to the Baerveldt implant. The primary outcome was any of the following: failure, defined as IOP outside target, with a 20% reduction from baseline, for two consecutive visits after three months; vision-threatening complications; de-novo glaucoma procedures; or loss of light perception.

This study confirms results reported by Budenz et al.¹ before in that both devices are effective in reducing IOP and the need for medications. Failure rates were higher for the a-priori definition of failure in Ahmed group (51%) than Baerveldt (34%; P = 0.03). The main reason for failure was high IOP, with a majority occurring during the first year postop.

At three years, visual acuity, number of de-novo glaucoma procedures, IOP, number of postoperative interventions, and complication rates were similar for both groups. However, the number of patients that required medications was significantly higher in the Ahmed group (75%) than in the Baerveldt group (50%). The authors report the Baerveldt group had more hypotony-related vision-threatening complications (seven) than in the Ahmed group (none). Unfortunately, the authors do not appear to have defined hypotony-related visionthreatening complications in the study design. They seem to have grouped them later, making this a post hoc analysis, as no individual serious complication rate was statistically different between the two groups except for encapsulated blebs (which occurred more frequently in the Ahmed group). A potential for bias exists in this conclusion. This study demonstrates that Baerveldt implants are superior for controlling refractory glaucoma at three years. Overall the data suggest there is not much difference in complication rates, but care must be taken to avoid complications that cause vision loss. However, the study did not report a difference in visual outcomes between the two groups, so the safety concerns noted by the authors may be overstated.

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