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P. Gouws, B.S. Elkin, G.E. Trope, R.C. Ethier; A New Valved Seton for Glaucoma Surgery . Invest. Ophthalmol. Vis. Sci. 2005;46(13):78.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Current glaucoma setons are either non–valved or have poorly performing valves, leading to irregular post operative IOP control. We have developed a new glaucoma valve to maintain IOP at a user–defined pressure. Here we report testing of this device in vitro and in vivo. Methods: In vitro tests were carried out by perfusing mock aqueous humor through the new devices at a variety of pressures using a syringe pump, and recording valve opening pressures with a pressure transducer. In vivo testing was carried out by implanting devices into one eye of each of two white New–Zealand rabbits. IOP was monitored non–invasively with a Tono–Pen before and after drainage shunt implantation in both operated and contralateral control eyes. After several weeks the eyes were enucleated and the device further tested using the in vitro system. Results: In vitro testing showed a clearly defined valve opening pressure of 6–12 mmHg, depending on the user–defined valve set point. In vivo, pre–operative IOP’s were 17–20 mmHg in rabbit eyes. The operated eyes showed consistent pressures of approximately 10 mmHg, while the un–operated contralateral eye maintained pressures of 17–20 mmHg. After one week the tube ostium was blocked by iris tissue in one eye, causing IOP to return to pre–operative levels. In the second rabbit, IOP gradually returned to pre–operative values after 2 weeks due to capsule formation around the device. After removal of the implanted eye in Rabbit #1 at day 31, the cornea was incised to expose the tube, which was then connected to the in vitro testing apparatus to monitor outflow. There was virtually no measurable flow until the fibrous capsule surrounding the valve was incised. The flow immediately showed a 60–fold increase (from 0.01to 0.60 µl/min/mmHg) consistent with an opening pressure of 6–10 mmHg. Additional animal tests are now underway. Conclusions: Initial tests show this device can lower IOP in vivo. The vast increase in outflow following incision of the tissue capsule around the explanted valve clearly shows that the failure of the implant was not due to the implant itself, but rather due to the capsule around the implant plate restricting flow. This new valved Seton is potentially clinically viable and offers an exciting option of lowering IOP while preventing hypotony.
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