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Ashutosh Richhariya, Swathi Vallabh Badakere, Nikhil Choudhari, Sai Naga Sri Harsha Chittajallu, Sirisha Senthil, Chandrasekhar Garudadri; Dynamics of Ahmed Glaucoma Valve® in vitro. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4967.
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A valved glaucoma drainage device can reduce the risk of early post-operative hypotony but has an opening pressure. This study was designed to evaluate whether the priming pressure or the area of separation of the valve leaflets during priming has any effect on performance of the Ahmed Glaucoma Valve® (AGV) (New World Medical, Rancho, USA), and to study the role of valve action under simulated physiological conditions.
Ten new AGV devices were tested. Each device was connected to a digital manometer and was primed with normal saline using a 5 cc syringe under a microscope fitted with a high speed digital camera (Figure 1; A & B). Subsequently, the AGV was placed in a saline bath and was connected to an open manometer, a digital manometer and an infusion pump. Saline was infused into the system at the rate of 3μL/min for 24 hours. Digital manometer readings were recorded at 4 Hz using computerized data logging. The pressure curves were plotted against time in MATLAB® (Mathworks Inc., Massachusetts, USA). Transient state opening pressure of AGV was defined as the peak pressure before attaining steady state (Figure 2). Opening and closing pressure was defined as the maximum and minimum pressure in steady state.
The mean (standard deviation; SD) priming pressure was 1173 (256) mm Hg. The mean duration (SD) of the transient phase was 357.5 (287.3) minutes. The transient state opening pressure varied between 8 and 45 mm Hg. The mean (SD) opening and closing pressures were 13.1 (2.6) mm Hg and 6.9 (1.2) mm Hg, respectively (Figure 2). The mean (SD) area of separation of valve leaflets & width of outlet nozzle showed increase from 6.2 (1.9) mm2 & 0.3 (0.1) mm during priming to 11.6 (1.4) mm2 and 1.8 (0.8) mm, respectively, when assessed after attaining the steady state. The correlation between priming & opening or closing pressure, and the area of leaflet separation or width of outlet nozzle & duration of transient phase was statistically insignificant.
The device undergoes a transient state of opening of valve leaflets beyond that in priming, before reaching the steady state. The priming pressure or the area of separation of the valve leaflets did not affect the steady state performance of AGV. The device functions as a valve which opens and closes intermittently in steady state.This study shows variable in vitro performance of AGV; however, the steady state pressures were in the desirable range.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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