Biomechanics of human trabecular meshwork in healthy and glaucoma eyes via dynamic Schlemm's canal pressurization

Alireza Karimi; Seyed Mohammadali Rahmati; Reza Razaghi; J Crawford Downs; Ted S Acott; Ruikang K Wang; Murray Johnstone

doi:10.1016/j.cmpb.2022.106921

Biomechanics of human trabecular meshwork in healthy and glaucoma eyes via dynamic Schlemm's canal pressurization

Comput Methods Programs Biomed. 2022 Jun:221:106921. doi: 10.1016/j.cmpb.2022.106921. Epub 2022 May 27.

Authors

Alireza Karimi¹, Seyed Mohammadali Rahmati², Reza Razaghi³, J Crawford Downs⁴, Ted S Acott⁵, Ruikang K Wang⁶, Murray Johnstone⁷

Affiliations

¹ Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, USA. Electronic address: akarimi@uabmc.edu.
² School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, USA. Electronic address: srahmati3@gatech.edu.
³ Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, USA.
⁴ Department of Ophthalmology and Visual Sciences, University of Alabama at Birmingham, Birmingham, AL, USA. Electronic address: cdowns@uabmc.edu.
⁵ Ophthalmology and Biochemistry and Molecular Biology, Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, USA. Electronic address: acott@ohsu.edu.
⁶ Department of Ophthalmology, University of Washington, Seattle, WA, USA; Department of Bioengineering, University of Washington, Seattle, WA, USA. Electronic address: wangrk@u.washington.edu.
⁷ Department of Ophthalmology, University of Washington, Seattle, WA, USA. Electronic address: murrayj2@uw.edu.

Abstract

Background and objective: The trabecular meshwork (TM) consists of extracellular matrix (ECM) with embedded collagen and elastin fibers providing its mechanical support. TM stiffness is considerably higher in glaucoma eyes. Emerging data indicates that the TM moves dynamically with transient intraocular pressure (IOP) fluctuations, implying the viscoelastic mechanical behavior of the TM. However, little is known about TM viscoelastic behavior. We calculated the viscoelastic mechanical properties of the TM in n = 2 healthy and n = 2 glaucoma eyes.

Methods: A quadrant of the anterior segment was submerged in a saline bath, and a cannula connected to an adjustable saline reservoir was inserted into Schlemm's canal (SC). A spectral domain-OCT (SD-OCT) provided continuous cross-sectional B-scans of the TM/JCT/SC complex during pressure oscillation from 0 to 30 mmHg at two locations. The TM/JCT/SC complex boundaries were delineated to construct a 20-µm-thick volume finite element (FE) mesh. Pre-tensioned collagen and elastin fibrils were embedded in the model using a mesh-free penalty-based cable-in-solid algorithm. SC pressure was represented by a position- and time-dependent pressure boundary; floating boundary conditions were applied to the other cut edges of the model. An FE-optimization algorithm was used to adjust the ECM/fiber mechanical properties such that the TM/JCT/SC model and SD-OCT imaging data best matched over time.

Results: Significantly larger short- and long-time ECM shear moduli (p = 0.0032), and collagen (1.82x) and elastin (2.72x) fibril elastic moduli (p = 0.0001), were found in the TM of glaucoma eyes compared to healthy controls.

Conclusions: These findings provide additional clarity on the mechanical property differences in healthy and glaucomatous outflow pathway under dynamic loading. Understanding the viscoelastic properties of the TM may serve as a new biomarker in early diagnosis of glaucoma.

Keywords: Collagen and elastin fibers; Finite element-optimization; Glaucoma; Ocular biomechanics; Trabecular meshwork.

MeSH terms

Biomechanical Phenomena
Cross-Sectional Studies
Elastin / metabolism
Glaucoma* / diagnostic imaging
Humans
Trabecular Meshwork* / metabolism

Substances

Elastin

Abstract

MeSH terms

Substances

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