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F May, M Salvodelli, JM Legeais; Glaucoma Valves and Drainage Devices: In Vitro Hydrodynamic Flow Characteristics . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3340.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To develop a protocol for evaluating the hydrodynamic characteristics of the glaucoma valves and drainage devices, using a range of flow-rate and pressure values approaching the ocular hydrodynamic conditions. Methods: The protocol is composed of 1) a scanning electronic microscopy study of the device surfaces exposed to flow, 2) an hydrodynamic analysis with determination of the opening pressure, of the closing pressure and of the facility of flow, and 3) a mode B echographic detection of the valve movements. The flow experiment set up consisted of four elements linked by perfusion tubing: a water manometer, a motor perfusion pomp, a pressure transducer, and a catheter connected to the glaucoma device. Perfusion fluid is demineralised water. Tests are performed at 20-25°C, using a range of low flow-rate values: 1 to 5 microlitres/mn. Results: The Molteno Implant behaves as a simple drain with a very high facility of flow. The device modelling the Krupin Valve behaves as a valve in air, but as a simple drain when immerged in water. The Ahmed Glaucoma Valve is the only one presenting a real valve behaviour with an opening pressure (22 to 37 mm Hg) and a closing pressure (-3,7 to 0,7 mm Hg) both without relation either with the perfusion flow-rate value or with the immersion hydrostatic presure. The Ahmed Valve presents an unexpected middle position of half-opening allowing a flow with a facility close to the trabecular facility. In each device, the surfaces seemed regular and smooth in electron microscopy. B mode echography allows detection of valve movements for the Ahmed device. Conclusion: This protocol allows classification of the glaucoma devices. Only the Ahmed device has a real valve behaviour, regulating the pressure within desired range, when exposed to flow-rate close to the aqueous outflow flow-rate values.
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