Abstract
Purpose :
While the optic nerve head (ONH) has shown a strong viscoelastic mechanical response with intraocular pressure change, computational simulations of ONH biomechanics have not incorporated the viscoelastic mechanical behavior of ONH tissues. Thus, in this study, we propose and test a mesh-free, beam-in-solid coupling algorithm to model the heterogeneous viscoelastic mechanical behavior of anisotropic collagen fibers within a viscoelastic scleral solid matrix.
Methods :
To characterize the differences in ONH biomechanics resulting from hyperelastic and viscoelastic scleral material formulations, an eye-specific finite element model of the posterior human eye was used that incorporates the full 3D microstructures of the load-bearing lamina cribrosa with interspersed laminar neural tissues. Two versions of the model were compared, representing the heterogeneous, anisotropic behavior of the collagenous sclera and pia as either hyperelastic solid matrix with embedded elastic cable elements, or viscoelastic solid matrix with embedded viscoelastic beam elements. We validated the viscoelastic material property approach against published experimental tensile tests of the human scleral patches and demonstrated its effectiveness in a complex model of the posterior human eye and ONH. ONH biomechanical responses were simulated with intraocular pressure and cerebrospinal fluid pressure changes typical of body position transition from sitting to supine, applied over 250 ms.
Results :
The ONH tissues showed larger stresses and strains in the supine body position compared to the sitting in both simulations, as expected (Table). While the laminar surface deforms more posteriorly (+6 µm) from the sitting to supine using a hyperelastic material model, it deforms more anteriorly (-5.7 µm) using the viscoelastic material model; radial scleral canal expansion at the anterior laminar insertion was ~50% smaller in the viscoelastic formulation (9 µm) compared to the hyperelastic formulation (19.8 µm). All results fell within the range of experimental observations.
Conclusions :
Although ONH stresses, strains and deformations were in the physiologic range for both models, there were substantial differences between the formulations, especially in deformation. Enhancing the accuracy of material formulations in ONH models should contribute to a better understanding of ONH biomechanics, but future work needs to be done to experimentally validate these results.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.