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The objective of this study was to evaluate which hyperelastic model could best describe the nonlinear mechanical behavior of the cornea, in order to characterize the capability of the non-linear model parameters to discriminate structural changes in a damaged cornea. Porcine corneas were used, establishing two different groups: control (non-treated) and NaOH-treated (damaged) corneas (n = 8). NaOH causes a chemical burn to the corneal tissue, simulating a disease associated to structural damage of the stromal layer. Quasi-static uniaxial tensile tests were performed in nasaltemporal direction immediately after preparing corneal strips from the two groups. Three non-linear hyperelastic models (i.e. Hamilton-Zabolotskaya model, Ogden model and Mooney-Rivlin model) were fitted to the stress-strain curves obtained in the tensile tests and statistically compared. The corneas from the two groups showed a non-linear mechanical behavior that was best described by the Hamilton-Zabolotskaya model, obtaining the highest coefficient of determination (R 2 > 0.95). Moreover, Hamilton-Zabolotskaya model showed the highest discriminative capability of the nonlinear model parameter (Parameter A) for the tissue structural changes between the two sample groups (p = 0.0005). The present work determines the best hyperelastic model with the highest discriminative capability in description of the non-linear mechanical behavior of the cornea. The cornea is the outermost layer of the eye, acting as a barrier against the external environment and as the main diopter of the visual system 1. Diseases that affect the cornea are one of the main causes of blindness in the world, ranking among the three most prevalent worldwide 2. Among those, corneal ectasia or corneal ectatic disorders stand as a main priority because of their incidence and impact in young population. These are corneal disorders, such as keratoconus or pellucid marginal corneal degeneration, that cause alterations in the corneal structure, leading to corneal topographical changes with decreased corneal thickness and abnormal corneal curvature 3. This abnormal structure of the cornea, as a result of non-linear mechanical changes, finally causes visual impairment to the patient. Currently, the diagnose of corneal degenerations and other corneal diseases are mainly based on structural measurements of the cornea (i.e. curvature, thickness, etc.), while some studies covered in-vivo non-structural measurements using Oculus Corvis ST and Ocular Response Analyzer systems 4-6. These new, non-invasive systems can analyze corneal biomechanical properties, such as corneal hysteresis, including an estimation of intraocular pressure. However, we propose that non-linear mechanical parameters can be obtained from non-invasive elastography or probing technologies such as non-linear torsional waves, non-linearity in probing, non-linearity by micro-indentation to be used in diagnostics in-vivo without removing the cornea 7-9. Hence, quantifying the non-linear mechanical parameters of soft tissu...
The objective of this study was to evaluate which hyperelastic model could best describe the nonlinear mechanical behavior of the cornea, in order to characterize the capability of the non-linear model parameters to discriminate structural changes in a damaged cornea. Porcine corneas were used, establishing two different groups: control (non-treated) and NaOH-treated (damaged) corneas (n = 8). NaOH causes a chemical burn to the corneal tissue, simulating a disease associated to structural damage of the stromal layer. Quasi-static uniaxial tensile tests were performed in nasaltemporal direction immediately after preparing corneal strips from the two groups. Three non-linear hyperelastic models (i.e. Hamilton-Zabolotskaya model, Ogden model and Mooney-Rivlin model) were fitted to the stress-strain curves obtained in the tensile tests and statistically compared. The corneas from the two groups showed a non-linear mechanical behavior that was best described by the Hamilton-Zabolotskaya model, obtaining the highest coefficient of determination (R 2 > 0.95). Moreover, Hamilton-Zabolotskaya model showed the highest discriminative capability of the nonlinear model parameter (Parameter A) for the tissue structural changes between the two sample groups (p = 0.0005). The present work determines the best hyperelastic model with the highest discriminative capability in description of the non-linear mechanical behavior of the cornea. The cornea is the outermost layer of the eye, acting as a barrier against the external environment and as the main diopter of the visual system 1. Diseases that affect the cornea are one of the main causes of blindness in the world, ranking among the three most prevalent worldwide 2. Among those, corneal ectasia or corneal ectatic disorders stand as a main priority because of their incidence and impact in young population. These are corneal disorders, such as keratoconus or pellucid marginal corneal degeneration, that cause alterations in the corneal structure, leading to corneal topographical changes with decreased corneal thickness and abnormal corneal curvature 3. This abnormal structure of the cornea, as a result of non-linear mechanical changes, finally causes visual impairment to the patient. Currently, the diagnose of corneal degenerations and other corneal diseases are mainly based on structural measurements of the cornea (i.e. curvature, thickness, etc.), while some studies covered in-vivo non-structural measurements using Oculus Corvis ST and Ocular Response Analyzer systems 4-6. These new, non-invasive systems can analyze corneal biomechanical properties, such as corneal hysteresis, including an estimation of intraocular pressure. However, we propose that non-linear mechanical parameters can be obtained from non-invasive elastography or probing technologies such as non-linear torsional waves, non-linearity in probing, non-linearity by micro-indentation to be used in diagnostics in-vivo without removing the cornea 7-9. Hence, quantifying the non-linear mechanical parameters of soft tissu...
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