Corneal deformation mapping and FE-based strain analysis via digital image correlation: biomechanical changes after CXL and laser refractive surgery
Accurate assessment of corneal mechanical properties is critical for understanding ocular biomechanics, predicting refractive surgery outcomes, and optimizing cross-linking (CXL) treatments. Conventional uniaxial tensile test is limited by non-physiological boundary conditions and simplified stress distributions. Inflation testing more closely reproduces the in vivo stress state but has traditionally lacked full-field deformation mapping. In this work, we present an integrated experimental-computational protocol combining inflation testing of freshly enucleated porcine eyes with high-resolution three-dimensional digital image correlation (3D-DIC). Fifteen corneas were analyzed across three cohorts: (i) de-epithelialized controls, (ii) CXL-treated (standard Dresden protocol), and (iii) anterior stromal ablation via femtosecond laser. Samples were subjected to controlled intraocular pressure (IOP) elevations up to 40 mmHg. The 3D-DIC approach provided dense, pointwise displacement and strain maps across the anterior surface, successfully quantifying the localized stiffening effects of CXL and the increased compliance induced by stromal ablation. These full-field kinematic data were integrated into a membrane-theory finite element framework to resolve principal in-plane strains, that were used for subsequent inverse modeling to derive anisotropic hyperelastic parameters of porcine corneal tissue. Overall, the method establishes an end-to-end route from physiologic loading to full-field strain mapping and constitutive parameter identification, enabling quantitative evaluation of treatment-induced biomechanical changes in the cornea.