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Thao Nguyen, Baptiste Coudrillier, Harry Quigley, Craig Boote; Scleral anisotropy and its effects on the optic nerve head biomechanics. Invest. Ophthalmol. Vis. Sci. 2013;54(15):55. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the effects of the collagen fiber structure of the sclera on the mechanical response of the sclera and the optic nerve head (ONH)
Specimen-specific inverse finite element models were developed to calculate the material properties of two normal human sclera (age 67, 71) subjected to inflation testing. A distributed fiber model incorporating wide-angle X-ray scattering (WAXS) measurements of the collagen structure was applied to describe the anisotropic elastic behavior of the sclera. The material parameters were used for micromechanical studies of the mechanical anisotropy at various length scales (0.5, 2, and 4 mm). The effects of the sclera fiber structure on the ONH mechanical response were evaluated by progressively filtering out local anisotropic features (Fig. 2).
The collagen structure of the midposterior sclera (MPS) showed large variations in the preferred fiber direction and degree of fiber alignment. The mechanical anisotropy of the MPS decreased with increasing length scale (Fig. 1). At the 4 mm length scale, the MPS was nearly isotropic. The anisotropy of the MPS had little effect on the mechanical response of the ONH. Modeling 71% of the MPS as isotropic caused minimal changes (< 1%) to the scleral canal expansion and posterior lamina bowing (Fig. 2, second row). In the peripapillary sclera (PPS), collagen fibers were circumferentially aligned with spatially heterogeneous degree of alignment. The deformation of the ONH was acutely sensitive to the spatially heterogeneous anisotropy of the PPS.
Alterations in the degree of fiber alignment within the PPS observed in glaucoma eyes (Pijanka et al., IOVS, 2012) may significantly impact the biomechanical environment of the ONH.
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