Modeling the Endothelial Glycocalyx Layer in the Human Conventional Aqueous Outflow Pathway

Abstract

A layer of proteoglycans and glycoproteins known as glycocalyx covers the surface of the trabecular meshwork (TM), juxtacanalicular tissue (JCT), and Schlemm’s canal (SC) inner wall of the conventional aqueous outflow pathway in the eye. This has been shown to play a role in the mechanotransduction of fluid shear stress and in the regulation of the outflow resistance. The outflow resistance in the conventional outflow pathway is the main determinant of the intraocular pressure (IOP) through an active, two-way, fluid–structure interaction coupling between the outflow tissues and aqueous humor. A 3D microstructural finite element (FE) model of a healthy human eye TM/JCT/SC complex with interspersed aqueous humor was constructed. A very thin charged double layer that represents the endothelial glycocalyx layer covered the surface of the elastic outflow tissues. The aqueous humor was modeled as electroosmotic flow that is charged when it is in contact with the outflow tissues. The electrical–fluid–structure interaction (EFSI) method was used to couple the charged double layer (glycocalyx), fluid (aqueous humor), and solid (outflow tissues). When the IOP was elevated to 15 mmHg, the maximum aqueous humor velocity in the EFSI model was decreased by 2.35 mm/s (9%) compared to the fluid–structure interaction (FSI) model. The charge or electricity in the living human conventional outflow pathway generated by the charged endothelial glycocalyx layer plays a minor biomechanical role in the resultant stresses and strains as well as the hydrodynamics of the aqueous humor.

Biomechanics of the JCT and SC Inner Wall Endothelial Cells with Their Basement Membrane Using 3D Serial Block-Face Scanning Electron Microscopy

“…This omission could have affected the calculated outflow resistance in the JCT and inner wall endothelial cells of SC with their basement membranes. While our previous numerical study has indicated that the glycocalyx in the outer trabecular beams of the aqueous outflow pathway does not significantly impact the wall shear stress and velocity of the aqueous humor [ 40 ], the role of versican in outflow resistance within the SC basement membrane requires further investigation.…”

“…However, it should be noted that the element edge length of the reconstructed FE mesh was larger than the voxel resolution (0.0101 µm) of the SBF-SEM images. In order to ensure that the resulting strains and hydrodynamics in the outflow tissues were independent of the number of elements, mesh density analyses were conducted [ 25 , 36 , 37 , 40 ]. This was conducted to verify that the mesh density was appropriate and that the results were not affected by the mesh size.…”