Peripapillary and posterior scleral mechanics--part I: development of an anisotropic hyperelastic constitutive model.
Peripapillary and posterior scleral mechanics--part I: development of an anisotropic hyperelastic constitutive model.
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DOI：
10.1115/1.3113682
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发表时间：
2009-05
期刊：
影响因子：
--
通讯作者：
Suh JK
中科院分区：
文献类型：
--
作者：
Girard MJ;Downs JC;Burgoyne CF;Suh JK
巩膜是白色的外壳，是眼睛的主要承重组织，负责维持眼压。我们假设，后巩膜的机械性能在青光眼的发展中起着重要作用，并被青光眼的发展所改变。青光眼是一种眼科疾病，表现为视神经头部的结构性损害。提出了一种各向异性超弹性本构模型来模拟急性眼压升高下后巩膜的力学行为。本构模型从纤维增强复合材料理论出发，考虑了纤维增强胶原纤维的拉伸硬化效应。假设胶原纤维在局部材料点处呈多向排列，局限于与巩膜表面相切的平面内，用半圆形von-Mise分布描述。引入一个模型参数，即纤维浓度因子，用于控制胶原纤维沿优先纤维方向的排列。为了研究巩膜胶原纤维排列对后巩膜和视神经头整体行为的影响，对一只理想化的眼睛进行了有限元模拟。分析的四个输出量分别是巩膜管扩张量、巩膜管扭转量、后巩膜管变形量和后板层变形量。巩膜内的环状纤维组织抑制了巩膜管扩张，但造成了后部板层变形，而经线纤维组织则相反。此外，纤维浓度系数作为考虑的输出的放大参数。目前的模型模拟表明，后巩膜对视神经头的整体行为有很大的影响。因此，为这种组织提供准确的机械性能是最基本的。在一篇文章中，我们提出了一种测量猴后巩膜三维变形的方法，并基于所提出的本构模型，采用逆有限元方法提取力学特性。
The sclera is the white outer shell and principal load-bearing tissue of the eye as it sustains the intraocular pressure. We have hypothesized that the mechanical properties of the posterior sclera play a significant role in, and are altered by the development of glaucoma – an ocular disease manifested by structural damage to the optic nerve head. An anisotropic hyperelastic constitutive model is presented to simulate the mechanical behavior of the posterior sclera under acute elevations of intraocular pressure. The constitutive model is derived from fiber-reinforced composite theory, and incorporates stretch-induced stiffening of the reinforcing collagen fibers. Collagen fiber alignment was assumed to be multi-directional at local material points, confined within the plane tangent to the scleral surface, and described by the semi-circular von-Mises distribution. The introduction of a model parameter, namely the fiber concentration factor, was used to control collagen fiber alignment along a preferred fiber orientation. To investigate the effects of scleral collagen fiber alignment on the overall behaviors of the posterior sclera and optic nerve head, finite element simulations of an idealized eye were performed. The four output quantities analyzed were the scleral canal expansion, the scleral canal twist, the posterior scleral canal deformation and the posterior laminar deformation. A circumferential fiber organization in the sclera restrained scleral canal expansion but created posterior laminar deformation, whereas the opposite was observed with a meridional fiber organization. Additionally, the fiber concentration factor acted as an amplifying parameter on the considered outputs. The present model simulation suggests that the posterior sclera has a large impact on the overall behavior of the optic nerve head. It is therefore primordial to provide accurate mechanical properties for this tissue. In a companion paper , we present a method to measure the 3-D deformations of monkey posterior sclera and extract mechanical properties based on the proposed constitutive model with an inverse finite element method.
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