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Scleral anisotropy and its effects on the mechanical response of the optic nerve head

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Abstract

This paper presents a computational modeling study of the effects of the collagen fiber structure on the mechanical response of the sclera and the adjacent optic nerve head (ONH). A specimen-specific inverse finite element method was developed to determine the material properties of two human sclera subjected to full-field inflation experiments. A distributed fiber model was applied to describe the anisotropic elastic behavior of the sclera. The model directly incorporated wide-angle X-ray scattering measurements of the anisotropic collagen structure. The converged solution of the inverse method was used in micromechanical studies of the mechanical anisotropy of the sclera at different scales. The effects of the scleral collagen fiber structure on the ONH deformation were evaluated by progressively filtering out local anisotropic features. It was found that the majority of the midposterior sclera could be described as isotropic without significantly affecting the mechanical response of the tissues of the ONH. In contrast, removing local anisotropic features in the peripapillary sclera produced significant changes in scleral canal expansion and lamina cribrosa deformation. Local variations in the collagen structure of the peripapillary sclera significantly influenced the mechanical response of the ONH.

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Notes

  1. http://sourceforge.net/projects/tahoe/.

  2. http://www.mathworks.com/matlabcentral/fileexchange/8998.

  3. http://dakota.sandia.gov/software.html.

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Acknowledgments

Baptiste Coudrillier and Thao D. Nguyen would like to thank Dr. Victor Barocas and Dr. Peter Pinsky for helpful discussions regarding this work. This work was supported in part by the Public Health Service Research Grants EY021500 (Thao D. Nguyen), EY02120 and EY01765 (Harry A. Quigley and Wilmer Institute), the Fight For Sight grant 1360 (Craig Boote), the Leonard Wagner Charitable Trust, William T. Forrester, and Saranne and Livingston Kosberg (Harry A. Quigley).

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Authors and Affiliations

  1. Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD, 21218, USA

    Baptiste Coudrillier & Thao D. Nguyen

  2. Structural Biophysics Group, School of Optometry and Vision Sciences, Cardiff University, Cardiff, CF24 4LU, Wales, UK

    Craig Boote

  3. Glaucoma Center of Excellence, Wilmer Ophthalmological Institute, Johns Hopkins University School of Medicine, Baltimore, MD, 21218, USA

    Harry A. Quigley

Authors
  1. Baptiste Coudrillier
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  2. Craig Boote
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  3. Harry A. Quigley
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  4. Thao D. Nguyen
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Corresponding author

Correspondence to Baptiste Coudrillier.

Appendix: Effects of the midposterior sclera fiber structure on the mechanical response of the ONH for FC71r

Appendix: Effects of the midposterior sclera fiber structure on the mechanical response of the ONH for FC71r

The study of paragraph 3.4.1 was repeated for FC71r. Figure 23 shows the evolution of the area of the sclera described as isotropic with increasing values of anisotropic ratio threshold. Figure 24 plots the evolutions of the deformation of the ONH with increasing isotropic area.

Fig. 23
figure 23

A white square represents a WAXS measurement for which the anisotropic ratio is below the anisotropic ratio (AR) threshold indicated on top of the figure. An isotropic (constant) probability density function was used to describe the fiber structure of the white square regions instead of the normalized WAXS measurements. The portion of the sclera modeled as isotropic increased with increasing anisotropic ratio threshold

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Fig. 24
figure 24

Evolution of the ONH deformation as the sclera became more isotropic (Fig. 23). The posterior deformation of the LC decreased with increasing isotropic area. The scleral canal expansion and maximum principal tensile and shear LC strains increased with increasing isotropic area. Increasing the threshold to \(\text{ AR}=1.4\) converted sclera specimen to an isotropic material. Yet, this caused changes to the deformation response of the ONH. The star corresponds to the fully isotropic model

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Coudrillier, B., Boote, C., Quigley, H.A. et al. Scleral anisotropy and its effects on the mechanical response of the optic nerve head. Biomech Model Mechanobiol 12, 941–963 (2013). https://doi.org/10.1007/s10237-012-0455-y

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