Mechanical anisotropy of porcine cornea and correlation with stromal microstructure

An experimental study was conducted to determine the variation of biomechanical properties with anatomical orientation in porcine corneas. Strip specimens extracted from fresh porcine corneas were subjected to cycles of uniaxial tension while monitoring their behaviour. The specimens were extracted from either the superior-inferior (vertical), temporal-nasal (horizontal) or diagonal direction. Comparisons of behaviour were limited to specimens taken from the same animal to avoid the natural variation of biomechanical properties in corneas from different animals. The specimens were subjected to three different strain rates to check if the behaviour comparisons were affected by the cornea's viscoelasticity. Overall, vertical and horizontal specimens were found to have almost the same behaviour, and both were marginally stiffer than diagonal specimens (by 2-8%). This almost isotropic biomechanical behaviour was compatible with earlier indications of similar collagen fibril densities in the three main orientations of porcine corneas.