Modeling and Characterization of a Valved Glaucoma Drainage Device With Implications for Enhanced Therapeutic Efficacy

Abstract

We report on modeling and bench test results targeted at better understanding of valved glaucoma drainage devices (GDDs), a common current surgical treatment for glaucoma. A simple equivalent circuit is described to model fluid mechanical behavior of the aqueous humor in an eye with glaucoma, both before and after implantation of a valved GDD. Finite element method simulations (FEM), based on the lubrication-von Kármán model, are then performed to analyze the valve's mechanical and fluidic performance. Using nanoporous membranes to mimic the in vivo fibrous capsule, we have developed a microfluidic bench test to simulate the aqueous humor flow and the post-implantation fibrous tissue encapsulation around the GDD back plate. Our numerical and bench test results show that, contrary to the prevailing belief, the valve significantly contributes to the total pressure drop even after fibrous capsule formation. Furthermore, we show that bypassing the valve through a simple polyimide tube insertion will dramatically lower the intraocular pressure (IOP) after fibrous capsule formation. This may offer a new treatment option in some patients with advanced glaucoma.

In VitroFluid Dynamics of the Ahmed Glaucoma Valve Modified with Expanded Polytetrafluoroethylene

“…This stent lowered IOP by 7-8 mm Hg at a flow rate of 2.5 microliters per minute. 33 Ultimately, our goal is to reduce the progressive fibrosis that occurs adjacent to the drainage device. Porous implant morphology is known to induce a less fibrotic foreign body reaction.…”

The Ahmed Versus Baerveldt Study

“…When a strict IOP criteria of 14 mmHg was used, failure rates were high in both groups (76% Ahmed, 66% Baerveldt; P ¼ 0. 19). …”

Novel Micromachined Valved Glaucoma Drainage Devices

“…The most important problems that affect the design of GDDs are immediate hypotony and overgrowth of the bleb, tube fit and blockage and valves not closing [2] [3]. Loss of pressure (Hypotony) immediately after the operation is a major problem that has to be overcome as well.…”