Ahmed vs. Baerveldt: 3-year outcomes similar

Three-year outcomes of the Ahmed Baerveldt Comparison Study failed to demonstrate clear superiority of one implant over the other, although the Baerveldt group trended toward greater efficacy and there were fewer complications in the Ahmed group; an observation noted at one year that persisted at three years..

The Ahmed Baerveldt Comparison Study randomized 276 patients with uncontrolled glaucoma to receive either the Ahmed-FP7 Glaucoma Valve or a Baerveldt-350 Glaucoma Implant. Success was defined  as IOP >21 mmHg or less than a 20% reduction below baseline on two consecutive study visits after three months, IOP ≤5 mmHg on two consecutive study visits after three months, reoperation for glaucoma, loss of light perception vision, or removal of the implant for any reason.

There was no statistically significant difference between the two implant groups with regard to the primary outcome measure. Both procedures significantly decreased IOP and medication use three years from baseline. The AGV group had a higher rate of reoperation for glaucoma than the BGI group, but this was of borderline significance (P = 0.054). The mean IOP was 1.2 mmHg lower at three years with the BGI. Although this difference was not statistically significant (P = 0.086). Additionally, the authors note that the BGI group received fewer postoperative IOP-lowering medications at the three-year time point, a difference that was statistically significant (P = 0.020).

Most Ahmed valve failures (79%) were due to high IOP and most Baerveldt failures (55%) were due to low IOP or complications. Although the rate of complications was not significantly different between the groups, the Baerveldt group was more likely to undergo reoperation for a complication or have ≥ 2 lines of Snellen vision loss.

The results of this study in comparison to the one-year results can possibly be explained by the effect of aqueous cytokines. The Ahmed implant receives the “glaucomatous” aqueous onto its plate surface at the time of surgery. This aqueous has been shown to contain high levels of cytokines. This results in an early inflammatory reaction in the bleb wall causing early fibrosis and an early rise in pressure. This results in the bleb itself maintaining the inflammatory reaction by producing its own cytokines, which keeps the pressure up.

In contrast, the Baerveldt implant receives the aqueous when the IOP has been lowered by the drainage slit in the tube and thus has lower cytokine content and less fibrosis and a constantly lower pressure than the Ahmed.