Estimating human trabecular meshwork stiffness by numerical modeling and advanced OCT imaging

• Type of Material: Article
• Authors: Ke Wang, Emory University; Murray A. Johnstone, University of Washington, Seattle; Chen Xin, University of Washington, Seattle; Shaozhen Song, University of Washington, Seattle; Steven Padilla, University of Washington, Seattle; Janice A. Vranka, OHSU School of Medicine; Ted S. Acott, OHSU School of Medicine; Kai Zhou, Emory University; Stephen A. Schwaner, Emory University; Ruikang K. Wang, University of Washington, Seattle; Todd Sulchek, The George W. Woodruff School of Mechanical Engineering; Christopher Ethier, Emory University
• Language: English
• Date: 2017-09-01
• Publisher: Association for Research in Vision and Ophthalmology (ARVO)
• Publication Version: Final Published Version
• Copyright Statement: © 2017 The Authors.
• License: Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1167/iovs.17-22175
• Title of Journal or Parent Work: Investigative Ophthalmology & Visual Science
• ISSN: 0146-0404
• Volume: 58
• Issue: 11
• Start Page: 4809
• End Page: 4817
• Grant/Funding Information: Supported by the Georgia Research Alliance and National Institutes of Health Grants EY008247, EY010572, and EY025721 (TSA).
• Keywords: Trabecular Meshwork; Elastic Modulus; Tomography, Optical Coherence; Glaucoma; Humans; Finite Element Analysis; Male; Cadaver; Female; Aged; Aged, 80 and over
• Research Categories: Engineering, Biomedical; Engineering, Mechanical

Abstract

PURPOSE. The purpose of this study was to estimate human trabecular meshwork (hTM) stiffness, thought to be elevated in glaucoma, using a novel indirect approach, and to compare results with direct en face atomic force microscopy (AFM) measurements. METHODS. Postmortem human eyes were perfused to measure outflow facility and identify high- and low-flow regions (HF, LF) by tracer. Optical coherence tomography (OCT) images were obtained as Schlemm’s canal luminal pressure was directly manipulated. TM stiffness was deduced by an inverse finite element modeling (FEM) approach. A series of AFM forcemaps was acquired along a line traversing the anterior angle on a radially cut flat-mount corneoscleral wedge with TM facing upward. RESULTS. The elastic modulus of normal hTM estimated by inverse FEM was 70 ± 20 kPa (mean ± SD), whereas glaucomatous hTM was slightly stiffer (98 ± 19 kPa). This trend was consistent with TM stiffnesses measured by AFM: normal hTM stiffness = 1.37 ± 0.56 kPa, which was lower than glaucomatous hTM stiffness (2.75 ± 1.19 kPa). None of these differences were statistically significant. TM in HF wedges was softer than that in LF wedges for both normal and glaucomatous eyes based on the inverse FEM approach but not by AFM. Outflow facility was significantly correlated with TM stiffness estimated by FEM in six human eyes (P = 0.018). CONCLUSIONS. TM stiffness is higher, but only modestly so, in glaucomatous patients. Outflow facility in both normal and glaucomatous human eyes appears to associate with TM stiffness. This evidence motivates further studies to investigate factors underlying TM biomechanical property regulation.