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Baptiste Coudrillier, Jacek Pijanka, Craig Boote, Joan Jefferys, Harry Quigley, Thao Nguyen; Age and glaucoma-related changes in the anisotropic mechanical response of the sclera. Invest. Ophthalmol. Vis. Sci. 2013;54(15):70.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the effects of glaucoma and age on the mechanical anisotropy of the sclera and the biomechanical environment of the optic nerve head (ONH)
The biomechanical response to controlled-inflation was measured for 8 normal sclera from 7 donors and 10 glaucoma sclera from 6 donors (Coudrillier et al., Invest. Ophthalmol. Vis. Sci., 2012). Optic nerve cross-sections were graded in masked fashion to determine the presence of axon loss (Fig. 1). Wide-angle x-ray scattering (WAXS) was used to quantify collagen fiber orientation of the prior-inflated specimens (Pijanka et al., IOVS, 2012). Specimen-specific inverse finite element models were developed to calculate the material properties. The mechanical response of the sclera was described using a distributed fiber model incorporating WAXS measurement of the collagen structure. For each specimen, the map of the mechanical anisotropy and measures of the deformation of the ONH were computed (Coudrillier et al., Biomechan. Model. Mechanobiol., 2012). Outcome measures were compared using multivariate analyses accounting for the effects of age and glaucoma damage.
Preliminary results including the 8 normal sclera suggested that the mechanical anisotropy of the peripapillary sclera (PPS) follows a specific pattern with the temporal/superior (TS) quadrant being the most anisotropic and the superior/nasal (SN) quadrant being the least anisotropic (p<0.0001 for the comparison of SN and TN). Older age was predictive of a lower mechanical anisotropy in all quadrants (p=0.04, 0.01, 0.04 and 0.01 for SN, IT, NI, and TS, Fig. 2a), a non-significant increase in matrix stiffness (p=0.1, Fig. 2c), and a non-significant increase in fiber family stiffness (p=0.61, Fig. 2d).
This study will elucidate how alterations in the degree of fiber alignment within the PPS observed in glaucoma eyes (Pijanka et al., IOVS, 2012) impact the biomechanical environment of the ONH.
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