Priming the Ahmed Glaucoma Valve: Pressure Required and Effect of Overpriming

PURPOSE:To determine the pressure required to prime an Ahmed Glaucoma Valve (AGV) and determine whether the valve can be damaged by “over-priming pressure.” METHODS:Three AGVs, a syringe pump, and a manometer were used to assess priming pressure. Balanced salt solution was pumped through the AGV tube at increasing pressures until a jet of fluid was seen to eject from the AGV, as per manufacturer instructions. This was repeated 3 times for 3 different virgin AGVs giving the “priming pressure.” A second experiment used the same experimental set up to determine the “over-priming pressure” on 3 other AGVs. Fluid was pumped through the AGV at increasing pressures until evidence of damage was seen. The valve function was assessed before and after the “over-priming” stress test. Valve function was determined by the closing pressure, which is the pressure at which the valve closes and fluid was no longer seen passing through the valve. RESULTS:The priming pressure in the 3 AGVs was 2844, 3154, and 3051 mm Hg (mean, 3017±158 mm Hg). The maximum pressure generated using the syringe pump was 10,860, 10,343, and 10,860 mm Hg (mean, 10,688±299 mm Hg). No damage was observed in the valve mechanism. AGV closing pressure before the “over-priming” stress test was 8, 6, and 13 mm Hg and after the stress test was 6, 7, and 13 mm Hg. CONCLUSION:This study demonstrates that the priming pressure is consistent at around 3000 mm Hg. In addition, over-priming is not likely to damage or disturb the closing pressure.