Department of Ophthalmology, Duke University Medical Center, Durham, North Carolina, USA.
Curr Eye Res. 2011 Feb;36(2):112-7. doi: 10.3109/02713683.2010.512115.
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).
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 μl/min were applied and steady state pressure recorded. Resistance was calculated by dividing pressure by flow.
Modifying the Ahmed valve implant outflow with expanded ePTFE increased pressure and resistance. Pressure at a flow of 2 μl/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 μl/min was increased in the PRIME-Ahmed (5.8 ± 0.8 mm Hg/μl/min) when compared to the control implant (3.2 ± 0.6 mm Hg/μl/min).
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.
青光眼引流装置（GDD）长期降低眼内压的效果常常受到围绕 GDD 形成的纤维囊的限制。先前的研究表明，通过在 GDD 上添加多孔膜来对其进行修饰可促进囊形成具有血管化和更高渗透性的囊。本研究考察了在 Ahmed 阀的流出道被膨体聚四氟乙烯（ePTFE）多孔膜包裹后的体外流体动力学特性。
将对照和修饰的 Ahmed 植入物（命名为带有改良外壳的多孔 Retrofit 植入物或 PRIME-Ahmed）浸入盐水和明胶中，并在监测流量（Q）和压力（P）的系统中进行灌注。施加 1-50μl/min 的流速并记录稳态压力。阻力通过压力除以流量来计算。
用 ePTFE 对 Ahmed 阀植入物的流出道进行修饰会增加压力和阻力。在 PRIME-Ahmed（2μl/min 时为 11.6±1.5mmHg），相对于对照植入物（2μl/min 时为 6.5±1.2mmHg），在 2μl/min 流速时压力增加。在 PRIME-Ahmed（2μl/min 时为 5.8±0.8mmHg/μl/min），相对于对照植入物（2μl/min 时为 3.2±0.6mmHg/μl/min），在 2μl/min 流速时阻力增加。
用多孔膜修饰 Ahmed 阀的流出道会增加阻力，而阻力会随流速的增加而降低。Ahmed 阀植入物的行为类似于可变电阻。在低压力下它部分打开，并在生理流速下提供较低的阻力。
