Microstructure-based numerical simulation of the mechanical behaviour of ocular tissue

Area of Science:

• Biomedical Engineering
• Ocular Biomechanics
• Materials Science

Background:

• Ocular tissue biomechanics are crucial for understanding eye diseases and surgical outcomes.
• Age-related changes in ocular tissues, particularly collagenous structures, affect eye mechanics.
• Existing models often lack microstructural detail, limiting their predictive accuracy.

Purpose of the Study:

• To develop a novel, full-eye biomechanical material model incorporating microstructural collagen characteristics.
• To analyze age-related stiffening in ocular tissues using this advanced model.
• To validate the model against experimental data from aged human ocular tissues.

Main Methods:

• Reconstructed collagen fibril magnitude and orientation maps using Zernike polynomials from X-ray scattering data.
• Developed fine-mesh finite-element (FE) models with eye-specific geometry and a user-defined material model (UMAT).
• Employed iterative inverse modeling to derive material parameters matching experimental intraocular pressure-deformation data.

Main Results:

• The FE model accurately represented experimental intraocular pressure-deformation behavior (3.6-4.3% RMSE).
• Sensitivity analysis confirmed minimal impact of reduced orientation representation on FE solutions (0.08%).
• Demonstrated a consistent increase in mechanical stiffness across all ocular regions with advancing age.

Conclusions:

• A constitutive material model accurately representing ocular tissue biomechanics based on collagen distribution has been developed.
• The model provides precise control over stiffness and anisotropy throughout the ocular globe.
• This model has significant potential for applications in planning ophthalmic surgical and medical procedures.