Abstract
Purpose :
Prior models of extraocular mechanics have investigated a small range of horizontal eye rotation during which extraocular tissues have all been assumed isotropic despite evidence for anisotropy in the ON sheath (ONS). In order to clarify the role of ONS fiber orientation, we developed a FEM of adduction and abduction including experimentally observed translational eye displacement.
Methods :
The FEM implemented a hemisymmetric sclera, choroid, Bruch’s membrane, retina, ON and ONS based on MRI of the left eye of a 72-year-old Asian female donor who had normal tension glaucoma. Mechanical properties of eye tissues was based on preconditioned data for 17 human eyes where anisotropic properties in the ONS was measured in longitudinal and circumfrencial directions1. We simulated horizontal duction, alternatively considering an isotropic versus anisotorpic ONS tensile data1 fit to the to Holzapfel model. The stress/strain distribution of the ON was modeled using ABAQUS (Dassault Systemes) software. Eye movement starting from primary position consisted of ±32° rotation with associated lateral/axial translation.
Results :
During adduction from 0 to 32°, ON and ONS tensions were physiologically plausible, while stresses & strains were concentrated at the optic disc. At 32° adduction, for isotropic ONS, maximum principal strain reached ~45% in temporal peripapillary sclera, and stress reached ~35MPa in the temporal ONS. For the anisotropic ONS, these were reduced to ~30% and ~17MPa, respectively. At 32° abduction, maximum principal strain was highest in peripapillary sclera adjacent the nasal disc margin, but was greater at ~35% assuming isotropic than ~25% assuming an anisotropic ONS. Maximum principal stress during abduction was highest where nasal side of the ONS joined the sclera, and was greater at ~21MPa with isotropic than ~10MPa assuming ONS anisotropy.
Conclusions :
Simulating large horizontal duction including associated translation provides physiologically plausible results when incorporating of anaisotropic properties, inclusion of anisotropic ONS properties predicted lower stress and strain in the posterior eye. These results provide more realistic predictions of the mechanical effects of eye movements on tissues in around the optic disk.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.