Is Ahmed Glaucoma Valve Consistent in Performance?

To investigate the mechanism of action and consistency in flow characteristics of the Ahmed glaucoma valve (AGV) under simulated physiological conditions in-vitro and to evaluate whether resistance during priming has any effect on performance of the device.

Each newly opened AGV device was connected to a digital manometer and was primed with normal saline. The device was then placed in a saline bath and connected to an open manometer, a digital manometer, and an infusion pump. Saline was infused at a rate of 3 μL/min for 24 hours. Digital manometer readings were recorded at 4 Hz.

Data obtained from 9 devices are presented as medians (ranges). The priming pressure was 1130 (835, 1625) mm Hg. Pressure versus time curves showed two distinct phases; transient and steady phases. The transient phase peak pressure was 24 (13, 45) mm Hg. In the steady phase, opening and closing pressures were 13 (10, 17) and 7 (4, 9) mm Hg, respectively; the valve leaflets briefly opened every 73.9 (51, 76.6) minutes and the fluctuation of pressure (difference between opening and closing pressures) was 6 (3, 9) mm Hg. The Spearman correlation coefficient between priming and opening and priming and closing pressure was ρ = -0.13 (P = 0.72) and ρ = -0.36 (P = 0.33), respectively.

The device showed functionality like a valve. The resistance during priming did not affect opening and closing pressures of the AGV. This study showed variable in vitro performance of the AGV.

These laboratory findings might, at least partly, explain the variability in the clinical outcome of the device.