Jafari Somaye, Cai Shengqiang, Demer Joseph L
Department of Ophthalmology, Stein Eye Institute, Los Angeles, CA 90095, USA.
Department of Mechanical and Aerospace Engineering, University of California, San Diego, CA 92093, USA.
Bioengineering (Basel). 2025 May 29;12(6):587. doi: 10.3390/bioengineering12060587.
Previous models of extraocular mechanics have often assumed isotropic properties for ocular tissues, despite evidence indicating anisotropy in the optic nerve sheath (ONS). To investigate this further, we developed a finite element model (FEM) of horizontal eye rotation using MRI data from a living subject with normal tension glaucoma. Mechanical properties were derived from tensile tests on 17 post-mortem human eyes, revealing previously unrecognized anisotropic characteristics in the ONS. We simulated ±32° horizontal eye rotations and compared isotropic versus anisotropic ONS properties using the Holzapfel model. Strain distributions in the optic nerve (ON) were analyzed using ABAQUS 2024 software. During 32° adduction, stress and strain were concentrated at the ONS-sclera junction, reaching 8 MPa and 40% with isotropic properties, and 15 MPa and 30% with anisotropic properties. In contrast, during 32° abduction, stress was lower and strain was higher in the isotropic case (6 MPa and 30%) compared to the anisotropic case (12 MPa and 25%). Increased intraocular and intracranial pressures had minimal impact on the mechanical responses. These findings suggest that the anisotropic properties of the ONS increase stress concentration at the optic disc while reducing strain during eye movements, offering new insights into ocular biomechanics. A novel phenomenon emerged from the simulations: during larger ductions, the peripapillary Bruch's membrane is predicted to wrinkle, forming undulations with an approximately 20 μm amplitude and 100 μm wavelength at its interface with the retina and choroid.
以往的眼外肌力学模型常常假定眼组织具有各向同性特性，尽管有证据表明视神经鞘（ONS）存在各向异性。为了进一步研究这一问题，我们利用一名正常眼压性青光眼活体受试者的MRI数据，开发了一个水平眼球旋转的有限元模型（FEM）。通过对17只死后人类眼睛进行拉伸试验得出力学性能，揭示了ONS中此前未被认识到的各向异性特征。我们模拟了±32°的水平眼球旋转，并使用霍尔扎佩尔模型比较了各向同性与各向异性的ONS特性。使用ABAQUS 2024软件分析了视神经（ON）中的应变分布。在32°内收过程中，应力和应变集中在ONS - 巩膜交界处，各向同性特性下分别达到8 MPa和40%，各向异性特性下分别达到15 MPa和30%。相比之下，在32°外展过程中，各向同性情况下的应力较低且应变较高（6 MPa和30%），而各向异性情况下为（12 MPa和25%）。眼内压和颅内压升高对力学响应的影响最小。这些发现表明，ONS的各向异性特性在眼球运动过程中增加了视盘处的应力集中，同时降低了应变，为眼生物力学提供了新的见解。模拟中出现了一个新现象：在较大的眼球转动过程中，预计视乳头周围的布鲁赫膜会起皱，在其与视网膜和脉络膜的界面处形成振幅约为20μm、波长约为100μm的波动。
