Characterization of corneal biomechanical properties using experimental and computational methods

Cornea, the clear front part of the eye, opens a window for ocular examination. The importance of corneal biomechanics in the normal and pathological functions of the eye has gained its credibility in the past decades. The goal of our research is to better understand the potential role of ocular tissue biomechanical properties in the assessment of the ocular diseases. Specifically, we investigated roles of the corneal biomechanical properties in response to intraocular loading and the methods for non-invasive evaluation of corneal biomechanical properties.;The effect of corneal stiffness in intraocular pressure elevation responding to a rapid intraocular fluid accumulation was investigated on porcine eye globes. After corneal stiffening, the elevation of the intraocular pressure was significantly increased in the globes than those with non-stiffened corneas. An ultrasonic method combined with a wave propagation model was proposed to non-invasively evaluate corneal biomechanical properties. The accuracy of the estimated corneal biomechanical properties was evaluated with established techniques on porcine corneas and good agreement was achieved. The potential correlation between corneal acoustic properties measured by the ultrasound method and the mechanical properties from tensile test was examined on canine corneas. A strong correlation was found between corneal acoustic impedance and the corneal secant modulus in low strain levels. The ultrasound method was used to assess the effect of the corneal cross-links introduced by UVA irradiated riboflavin in keratoconus treatment. Significant corneal stiffness changes before and after corneal cross-linking were successfully detected by the ultrasound method. The ultrasound method was then applied to human volunteers in vivo in a pilot study. Cross-subject variation of corneal stiffness was observed. Finally, finite element method was used to investigate the interaction between ocular shell stiffness and intraocular pressure loads. The model predicts that a localized change of the stiffness on the ocular shell could significantly affect the displacement and stress of the shell.;Our studies showed that stiffened corneas induced substantially higher IOP elevations. The results suggested that corneal stiffness may play an important role in determining IOP elevation caused by an acute increase in the volume of intraocular fluid. The accuracy of the proposed ultrasound method has been demonstrated and the ultrasound method could be used to evaluate corneal stiffness non-invasively. The acoustic impedance of the cornea may be used as a surrogate of corneal elastic stiffness which is difficult to measure in vivo. We also found that the ultrasound method can detect the biomechanical changes induced by corneal cross-linking and the method is safe for clinical use. Our finite element model suggests that the cornea may affect the displacement and stress of the other tissue of the globe. The roles of corneal biomechanical properties in the pathophysiological function of the eye need further investigations.