Department of Ophthalmology and Stein Eye Institute, University of California, Los Angeles, CA, USA.
Department of Bioengineering, University of California, Los Angeles, CA, USA.
Biomech Model Mechanobiol. 2021 Aug;20(4):1353-1363. doi: 10.1007/s10237-021-01448-2. Epub 2021 Apr 20.
The optic nerve (ON) is a recently recognized tractional load on the eye during larger horizontal eye rotations. In order to understand the mechanical behavior of the eye during adduction, it is necessary to characterize material properties of the sclera, ON, and in particular its sheath. We performed tensile loading of specimens taken from fresh postmortem human eyes to characterize the range of variation in their biomechanical properties and determine the effect of preconditioning. We fitted reduced polynomial hyperelastic models to represent the nonlinear tensile behavior of the anterior, equatorial, posterior, and peripapillary sclera, as well as the ON and its sheath. For comparison, we analyzed tangent moduli in low and high strain regions to represent stiffness. Scleral stiffness generally decreased from anterior to posterior ocular regions. The ON had the lowest tangent modulus, but was surrounded by a much stiffer sheath. The low-strain hyperelastic behaviors of adjacent anatomical regions of the ON, ON sheath, and posterior sclera were similar as appropriate to avoid discontinuities at their boundaries. Regional stiffnesses within individual eyes were moderately correlated, implying that mechanical properties in one region of an eye do not reliably reflect properties of another region of that eye, and that potentially pathological combinations could occur in an eye if regional properties are discrepant. Preconditioning modestly stiffened ocular tissues, except peripapillary sclera that softened. The nonlinear mechanical behavior of posterior ocular tissues permits their stresses to match closely at low strains, although progressively increasing strain causes particularly great stress in the peripapillary region.
视神经（ON）是眼球在较大水平眼球转动过程中受到的一种新发现的牵拉负荷。为了了解内收过程中眼球的力学行为，有必要对巩膜、ON 及其鞘的材料特性进行特征描述。我们对取自新鲜尸检人眼的标本进行拉伸加载，以表征其生物力学性能的变化范围，并确定预处理的效果。我们拟合了简化的多项式超弹性模型来代表前、赤道、后和视盘周围巩膜以及 ON 和其鞘的非线性拉伸行为。为了进行比较，我们分析了低应变和高应变区域的切线模量来表示刚度。巩膜的刚度通常从前部到后部眼部区域逐渐降低。ON 的切线模量最低，但被更硬的鞘包围。ON、ON 鞘和后部巩膜相邻解剖区域的低应变超弹性行为相似，以避免在其边界处出现不连续性。个体眼中的区域刚度中度相关，这意味着一只眼中一个区域的机械性能不能可靠地反映该眼另一个区域的性能，如果区域性能存在差异，那么一只眼中可能会出现潜在的病理组合。预处理适度增强了眼球组织的刚度，除了视盘周围的巩膜变软。后部眼部组织的非线性力学行为允许它们在低应变时紧密匹配应力，尽管应变逐渐增加会导致视盘周围区域的应力特别大。
