부산대학교 도서관

Purpose: Long-term intraocular pressure reduction by glaucoma drainage devices (GDDs) is often limited by the fibrotic capsule that forms around them. Prior work demonstrates that modifying a GDD with a porous membrane promotes a vascularized and more permeable capsule. This work examines the in vitro fluid dynamics of the Ahmed valve after enclosing the outflow tract with a porous membrane of expanded polytetrafluoroethylene (ePTFE). Materials and Methods: The control and modified Ahmed implants (termed porous retrofitted implant with modified enclosure or PRIME-Ahmed) were submerged in saline and gelatin and perfused in a system that monitored flow (Q) and pressure (P). Flow rates of 1--50 μμl/min were applied and steady state pressure recorded. Resistance was calculated by dividing pressure by flow. Results: Modifying the Ahmed valve implant outflow with expanded ePTFE increased pressure and resistance. Pressure at a flow of 2 μμl/min was increased in the PRIME-Ahmed (11.6 ±± 1.5 mm Hg) relative to the control implant (6.5 ±± 1.2 mm Hg). Resistance at a flow of 2 μμl/min was increased in the PRIME-Ahmed (5.8 ±± 0.8 mm Hg/μμl/min) when compared to the control implant (3.2 ±± 0.6 mm Hg/μμl/min). Conclusions: Modifying the outflow tract of the Ahmed valve with a porous membrane adds resistance that decreases with increasing flow. The Ahmed valve implant behaves as a variable resistor. It is partially open at low pressures and provides reduced resistance at physiologic flow rates. [ABSTRACT FROM AUTHOR]