Corneal Dynamic Properties under Air Puff Excitation

Abstract

Propose: The aim of the study is to study the corneal dynamic properties under an air puff excitation. Methods: The corneal deformation response was modeled with nonlinear viscoelastic models. The nonlinear viscoelastic model consisted of a dashpot connected in parallel with a nonlinear spring with a stress-strain relationship of  = α[exp(βε)-1]. The corneal deformation response were modeled and compared with the clinical corneal dynamic deformation profile extracted from Corneal Visualization Scheimpflug Tonometer (Corvis ST) to estimate the corresponding corneal biomechanical parameters. Results: The magnitude of the maximum corneal deformation (ymax) showed a significant decrease of 17.3% – 33.3% with the increase of corneal material nonlinearity scaling factor α and stress-strain nonlinear component β, respectively. The magnitude of ymax are highly influenced by the nonlinear spring constants (α and β). β showed a more influence to the deformation response as compared to α as α introduces corneal stiffening in a scalar manner, while β introduces corneal stiffening in an exponential manner. ymax showed only 0.17% decrease in magnitude and a time delay of 0.31ms to reach the maximum deformation with the variation of corneal viscous damping coefficients. The corneal material nonlinearity dominated the corneal deformation behavior and the maximum corneal deformation under the air puff excitation, while the viscous component contributed slightly to the lateral shifting of the corneal deformation response and showed minimal influence to the magnitude and shape of the corneal deformation response profile. The simulated corneal deformation profile also showed a good fit with the clinical corneal dynamics deformation behavior under an air puff excitation. Conclusion(s): Corneal dynamic deformation under an air puff excitation can be modeled and can be used to estimate the corneal dynamic biomechanical properties in vivo.