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Kapil Krishnan, Vincent Libertiaux, Rafael Grytz, Christopher A Girkin, J Crawford C Downs; Eye-Specific Finite Element Modeling of Human Optic Nerve Head (ONH) Biomechanics. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2457. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To study the localized strain distribution in the ONH of anatomically accurate, eye-specific finite element (FE) models of human eyes. We study the effects of local, eye-specific laminar density (CTVF) and the predominant orientation of laminar beams (anisotropy) on the mechanical strain in the lamina cribrosa (LC).
Five right eyes from donors of European descent aged 55 to 89 years were immersion fixed at 10 mmHg within 6 hours postmortem. The eye-specific geometry and resulting FE models of the entire posterior pole (Figure) were created from high resolution 3D reconstructions of the ONH connective tissues acquired using a microtome-based serial sectioning and block face imaging device. The local heterogeneous, anisotropic, hyperelastic material properties for the LC were determined using an MIL-based approach, and the circumpapillary collagen fiber ring was incorporated into the properties for the sclera and pia. The 3D geometries of the sclera, retina, pia, pre- and retro-laminar tissues and the lamina cribrosa were meshed using quadratic tetrahedral elements (Figure). The eye-specific FE models were then pre-stressed from 0 to the baseline IOP of 10 mmHg and then loaded to a final pressure of 45 mmHg. Contour plots of von Mises and maximum principal (tensile) strains were compared to the contour plots of laminar connective tissue density (CTVF; Figure).
The regional patterns of both von Mises and tensile strain in the ONH at IOPs of 10 mmHg and 45 mmHg are inversely related to the regional laminar density (Figure) but the relationship with local anisotropy was less clear.
We developed and studied eye-specific FE models that incorporated realistic geometries of the ONH macro- and micro-structure, as well as complex heterogeneous, anisotropic, hyperelastic material properties. Within these models of normal human ONHs, high mechanical strains localized in regions with low laminar density.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
The eye-specific finite element model of a human donor optic nerve head. The cross-sectional view shows the various components of the model and the respective von Mises strain. The regional patterns of both von Mises and tensile strain in the ONH at 2 different pressures as well as the regional laminar densities are summarized.
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