Biaxial mechanical characterization and constitutive modelling of sheep sclera soft tissue

Constant exposure to the environment, head trauma and shaking of ocular tissues result in damage and disorders of the eye. In the United States, trauma alone causes about 30 000 people each year to lose vision in one eye. The sclera soft tissue plays a vital role in protecting, maintaining the shape of the eye and regulating the intraocular pressure, and is closely linked with glaucoma. The aim of the study was to investigate and compare the mechanical response of sheep sclera soft tissue under equibiaxial tension as data from such studies are limited. The material parameters describing the mechanical behaviour were determined using the Fung and Choi–Vito models. Sheep eyes were transported in ice and tested in saline solution at a temperature 37° C using within 4 to 6 hours after slaughter. Sheep sclera tissue was found to be nonlinear and anisotropic with average anisotropy constants (A) of 0.69 and 0.74 for the Fung and Choi–Vito models, respectively. The coefficients of correlation (R2 ) between the experimental and hyperelastic models were found to be 0.98 and 0.95 respectively, with Fung model providing the best fit and more anisotropic behaviour than the Choi–Vito model.