June 2021
Volume 62, Issue 8
Open Access
ARVO Annual Meeting Abstract  |   June 2021
Mechanical properties of scleral collagen fibers obtained using a new fiber-based specimen-specific model of sclera microstructure.
Author Affiliations & Notes
  • Fengting Ji
    Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
    Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
  • Manik Bansal
    Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
  • Bingrui Wang
    Mechanical Engineering, Southwest Jiaotong University, Chengdu, Sichuan, China
  • Yi Hua
    Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
  • Ian A Sigal
    Ophthalmology, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
    Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
  • Footnotes
    Commercial Relationships   Fengting Ji, None; Manik Bansal, None; Bingrui Wang, None; Yi Hua, None; Ian Sigal, None
  • Footnotes
    Support  Supported in part by National Institutes of Health R01-EY023966, R01-EY028662, P30-EY008098 and T32-EY017271 (Bethesda, MD), the Eye and Ear Foundation (Pittsburgh, PA), and Research to prevent blindness.
Investigative Ophthalmology & Visual Science June 2021, Vol.62, 1652. doi:
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      Fengting Ji, Manik Bansal, Bingrui Wang, Yi Hua, Ian A Sigal; Mechanical properties of scleral collagen fibers obtained using a new fiber-based specimen-specific model of sclera microstructure.. Invest. Ophthalmol. Vis. Sci. 2021;62(8):1652.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : Scleral collagen fiber mechanical properties are central to overall eye mechanics, and thus multiple techniques have been used to determine them using modeling. Most models, however, use continuum approaches that do not consider critical characteristics of the fibers. Our goal was to determine the fiber mechanical properties using a newly developed specimen-specific fiber-based model of sclera.

Methods : Two optic nerve heads (ONHs) were sectioned at 30 µm thickness, one coronally and the other sagittally. The sections were imaged using polarized light microscopy (PLM) to obtain local collagen fiber density and orientations in the section planes. Images of 17 serial coronal sections were registered to form a volume. A square region of sclera was selected and the fibers were traced in all images accordant to local fiber orientations (Fig 1). Fiber overlaps were resolved by an iterative algorithm. The out-of-plane fiber orientations were adjusted to match the sagittal PLM data. The fibers were then embedded in a matrix and the assembly was used in an inverse modeling process to derive fiber mechanical properties by matching published experimental biaxial extension data assuming a hyperelastic Mooney-Rivlin behavior.

Results : A model with 1016 fibers was constructed. Wilcoxon rank sum tests showed that fiber orientations were not significantly different between the model and histology for both coronal (p>0.7) and sagittal (p>0.6) directions. The estimated fiber stiffness was 1488.7MPa (Fig 2).

Conclusions : Our fiber-based sclera model incorporated detailed specimen-specific architecture, and previously ignored fiber-level mechanics, such as fiber-fiber interactions and long-distance load transfer. Although the model predicts higher fiber stiffness than previous studies (e.g. Grytz et al. 2013), the biomechanical behavior was in excellent agreement with experiments.

This is a 2021 ARVO Annual Meeting abstract.

 

(A) Coronal and (B) sagittal ONH sections were imaged using PLM to obtain fiber orientation. (C) The sections were registered to build a volume. (D) Fibers were defined according to the PLM orientations (E, F) and adjusted iteratively until the model matched the PLM images in both directions.

(A) Coronal and (B) sagittal ONH sections were imaged using PLM to obtain fiber orientation. (C) The sections were registered to build a volume. (D) Fibers were defined according to the PLM orientations (E, F) and adjusted iteratively until the model matched the PLM images in both directions.

 

(A) Model before test. (B, C) After stretch, the behaviors of fibers were inhomogeneous with varying deformations and stresses at microscale. (D, E) An excellent fit with the experiment was achieved.

(A) Model before test. (B, C) After stretch, the behaviors of fibers were inhomogeneous with varying deformations and stresses at microscale. (D, E) An excellent fit with the experiment was achieved.

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