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E. B. Moss, G. E. Trope; Evaluation of Closing Pressure in Ahmed Glaucoma Valve. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3964.
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To determine Ahmed Glaucoma Valve (AGV) closing pressure (CP) using a simple gravity-driven bench-top system with a fixed volume of perfusate.
Six AGV, model FP7, were perfused with 1 ml Balanced Salt Solution (BSS) then assessed in 5 sequential test runs. The devices were submerged under 1.5 cm of BSS and connected at the inlet tube via a blunt 26-guage cannula to a manometer filled with BSS to a height of 680 mm (50 mmHg) above the valve. Each 90-minute test commenced when a stopcock between the manometer and the valve was opened, permitting flow through the device. To determine the effect of capillarity in the system, control runs were executed with AGV removed from the apparatus. The presented closing pressures represent the difference in pressure head at 90 minutes between test runs and control.
All six AGV exhibited valve closure, maintaining pressure head of at least 2.5 mmHg above control levels. Mean CP was 8.2 Â± 5.0 mmHg with a range of 2.5 to 14.6 mmHg. Variation in CP between the five runs within the testing of individual valves resulted in standard deviations greater than 25% of the mean CP values in four of the six valves tested.
The results of this in vitro testing suggest that as pressure is reduced, the Ahmed FP7 is capable of closing to flow, thus maintaining a pressure head, but it is prone to variations in closing pressure both within trials of individual valves and between different valves.
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