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I.A. Sigal, J.G. Flanagan, C.R. Ethier; Efects of Tissue Stiffness on Acute Deformation of Patient–Specific Optic Nerve Head Tissues . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1227.
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© ARVO (1962-2015); The Authors (2016-present)
The biomechanical environment within the optic nerve head (ONH) is believed to play a role in the pathogenesis of glaucomatous optic neuropathy. Biomechanical forces depend on the detailed anatomy and material properties of the tissues that form the ONH. Previous modeling studies (IOVS, 2005, 46:4189) using generic ONH models suggested that scleral properties have a large effect on ONH biomechanics. Here we extend this work by using individual–specific ONH models.
We used a previously described method to create computational models of the ONH of both eyes of three donors. In brief, micrographs of stained serial sections of the ONHs were segmented, and used to define the geometry of the individual–specific 3D models with five components: sclera, lamina cribrosa, pre and post–laminar neural tissue and pia mater. We carried out a parametric analysis by varying 6 input factors: the five Young’s moduli (stiffnesses) of each constitutive tissue and the compressibility of the pre–laminar neural region. All materials were assumed linearly elastic and isotropic. The pre–laminar neural tissue compressibility was varied from somewhat compressible (υ=0.4) to effectively incompressible (υ=0.4999). The input factors were varied independently, and for each configuration commercial finite element software (ANSYS v8) was used to predict the biomechanical response to changes in IOP. Response was quantified through the peak and mean strain (% elongation) within each tissue.
Varying the scleral stiffness had the largest influence on all outcome measures, across all ONH models. For example, increasing scleral stiffness from 2 – 12MPa tripled the maximum principal strain within the pre–laminar neural tissue, whereas at any given configuration differences from one model to another were less than one third as large.Neural tissues stiffnesses had the smallest influences, while the lamina cribrosa and pia mater stiffness, and the prelaminar neural tissue compressibility each influenced some outcome measure, but not others.
Scleral biomechanical properties have a large influence on ONH biomechanics, independent of individual–specific variations in ONH anatomy. Our results show that the mechanical insult to ONH tissues depends more on scleral properties than the detailed anatomy of the ONH. Inter–individual differences in scleral biomechanical properties need to be investigated.
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