Modulation of Outflow Facility and Biomechanics

PROJECT SUMMARY Primary open angle glaucoma (POAG) is a leading cause of irreversible blindness, and elevated intraocular pressure (IOP) is the primary risk factor. By 2040, it is predicted that 112 million people worldwide will have glaucoma. The IOP is maintained through a dynamic balance between the production and drainage of the

aqueous humor primarily via the trabecular meshwork (TM), juxtacanalicular connective tissue (JCT), and Schlemm's canal (SC) endothelium of the conventional outflow pathway. Outflow tissues are hyperviscoelastic (large-deformation and pressure-dependent) and dynamically interact with aqueous humor through an active,

two-way, fluid-structure interaction coupling. While glaucoma affects the morphology and mechanical properties of the outflow tissues, the biomechanical and hydrodynamics states in glaucoma eyes are still largely unknown. Assessment of the dynamic biomechanical properties of the TM, JCT, and inner wall endothelial cells of SC with

their basement membrane tissues in normal and disease will improve our understanding of the mechanisms of IOP regulation and the dynamic outflow resistance and could be a target for new diagnostic and therapeutic biomarkers in glaucoma. The goal of this project is to assess the biomechanical and hydrodynamic effects

of different drugs and treatments on outflow facility modulation through an inverse finite element method coupled with an optimization algorithm and advanced OCT imaging data. In this project, the low-flow (LF) and high-flow (HF) regions in human donor eyes will be determined by confocal imaging of the FluoSpheres in

the outflow pathway. Two-photon excitation microscopy will be used to measure the velocity of microbeads in the TM while the SC is negatively pressurized. The TM/JCT/SC complex in the LF and HF regions will be dissected and subject to tensile loading until failure. The elastic moduli of the normal and glaucomatous human

donor eyes in the LF and HF regions will be calculated. A quadrant of the anterior segment from normal and glaucomatous human donor eyes in LF and HF regions will be positively and negatively pressurized and imaged using a visible-light green OCT. The TM, JCT, SC inner wall boundaries in a course of dynamic motion will be

segmented using a deep neural network algorithm to reconstruct a finite element mesh of the TM, with the adjacent JCT and the SC inner wall. A mesh-free, beam-in-solid material-modeling algorithm will be used to distribute the collagen fibrils into the ECM of the TM and JCT. An inverse finite element method will be coupled

with an optimization algorithm to characterize the ECM/collagen fibrils hyperviscoelastic mechanical properties in the LF and HF regions such that the TM, JCT, SC inner wall dynamic motion and OCT imaging data best match over time. 3D finite element model of the TM/JCT/SC complex will be reconstructed using the OCT images

and will be subject to aqueous humor pressure elevation using fluid-structure interaction method. The biomechanical and hydrodynamics of the outflow pathway will be modeled and validated versus the digital volume correlation data (OCT images) and two-photon excitation microscopy/3D particle image velocimetry data.