The authors report the one-year outcomes from a five-year, randomized, controlled, multicenter study comparing IOP control and complications between the Ahmed-FP7 valve implant and the Baerveldt-350 implant. At one year, the Baerveldt group had a higher success rate, lower mean IOP and lesser mean medication requirement, but required a greater number of interventions.
These results are similar to those reported from a nearly identical randomized, controlled trial comparing the two devices published in the March issue of Ophthalmology, and it confirms retrospective studies on the subject.
This latest multicenter trial randomized 238 patients with uncontrolled glaucoma to receive either the Ahmed-FP7 valve implant or a Baerveldt-350 implant. The two treatment groups did not differ in any baseline characteristics with the exception of sex, with a greater proportion of women in the Baerveldt group (P=0.01). The primary outcome measure was failure, defined as IOP out of target range (5 to18 mmHg with ≥20 percent reduction from baseline) for two consecutive visits after three months, vision-threatening complications, additional glaucoma procedures or loss of light perception. Secondary outcome measures included IOP, medication use, visual acuity, complications and interventions.
At one year, the cumulative probability of failure was higher in the Ahmed group (43 percent vs. 28 percent, P=0.02). Mean IOP was 16.5±5.3 mmHg in the Ahmed group and 13.6±4.8 mmHg in the Baerveldt group (P < 0.001). The mean number of glaucoma medications required was 1.6±1.3 in the Ahmed group and 1.2±1.3 in the Baerveldt group (P=0.03). Visual acuity was similar in both groups at all visits in the first year (P=0.66).
While the postop complication rate was similar between the groups (45% Ahmed, 54% Baerveldt, P=0.19), the Baerveldt group required more interventions (42 percent vs. 26 percent).
Once again factors such as plate size and plate material, commonly assumed to play a role in IOP control, do not seem to play a large role in outcomes. Failure is due to bleb encapsulation, and the only real difference between the implants remains the presence of a valve, which allows access of aqueous onto the plate surface immediately. The well-documented presence of pro-inflammatory substances in the aqueous may produce early inflammation and more intense fibrosis in the subsequent capsule of the valved implant resulting, eventually, in higher IOP. Five-year results from this study will be interesting.
While outcomes were better with the Baerveldt implant, the authors caution that other factors such as surgical skill and patient risk factors for failure, medication tolerance, and compliance with therapy, should be considered before selecting a device.