Effects of variable permeability on aqueous humor outflow

All previous efforts to quantify the aqueous humor (AH) outflow resistance in the juxtacanalicular tissue (JCT) of the human eye have attempted to treat the tissue as a homogeneous porous material. In this study, we treat the JCT as a heterogeneous tissue with variable permeability. The variable permeability of each sub-region of the JCT is estimated from Quick-Freeze/Deep-Etch images using Karmen-Kozeny theory. Finite element simulations of the fluid flow using Darcy's law are computed at a micron resolution using a parallel algebraic multigrid (AMG) algorithm. Analyzing strictly the JCT, the overall resistance of this tissue is increased by 35-68% when assuming variable permeability instead of a homogenous tissue. Further, the resistance increase associated with the inclusion of the IW is 2-5 fold greater with a heterogeneous tissue compared to a homogeneous tissue. Because cellular and extracellular structures become denser proximal to the inner wall (IW) endothelium, resistance to AH outflow in this region of the JCT and funneling effects created by pores of the IW become amplified. Overall, the resistance of the JCT/IW domain is under-predicted when treating the JCT as a homogeneous tissue.