Whole-Eye Stress-Strain Index Mapping from Collagen Microstructure: A Finite Element Approach to Assess Scleral and Corneal Biomechanics

To develop and demonstrate a whole-eye Stress–Strain Index (SSI) mapping technique—where SSI represents a quantitative measure of ocular tissue stiffness—by extending an established corneal SSI method to the sclera, enabling regional biomechanical characterization of the entire ocular globe and simulation of pathological alterations. Collagen fibril distributions from seven human eyes were quantified using wide-angle-X-ray scattering and incorporated into anisotropic finite element (FE) models covering whole eye globe, and based on fibril-informed constitutive laws. An inverse analysis approach was employed to scale regional stiffness, aligning displacement patterns between the anisotropic FE models (based on fibril distribution) and corresponding isotropic FE models, which had uniform stiffness derived from SSI measurements, to generate SSI maps.Simulations were then performed to evaluate physiological aging, altered scleral thickness, posterior scleral stiffness reduction (myopia models), and localized weakening (staphyloma). Healthy eyes exhibited SSI distributions consistent with known collagen organization, showing elevated stiffness at the limbus and peripapillary sclera. SSI increased with age and was largely independent of scleral thickness. Posterior stiffness reductions of 30–60% (simulating conditions in myopic eyes) produced 38–170% increases in posterior displacement, with minimal corneal impact, while localized weakening of 50% (simulating staphyloma) resulted in an 87% increase in posterior pole displacement. Whole-eye SSI mapping provides a robust and physiologically consistent framework for characterizing regional ocular biomechanics. The method exploits established microstructural–mechanical relationships and enables realistic simulation of pathological scleral weakening, offering potential applications in the diagnosis, prognosis, and treatment planning of myopia, staphyloma, and related disorders.