Material Properties from Air Puff Corneal Deformation by Numerical Simulations on Model Corneas

Abstract

ObjectiveTo validate a new method for reconstructing corneal biomechanical properties from air puff corneal deformation images using hydrogel polymer model corneas and porcine corneas.MethodsAir puff deformation imaging was performed on model eyes with artificial corneas made out of three different hydrogel materials with three different thicknesses and on porcine eyes, at constant intraocular pressure of 15 mmHg. The cornea air puff deformation was modeled using finite elements, and hyperelastic material parameters were determined through inverse modeling, minimizing the difference between the simulated and the measured central deformation amplitude and central-peripheral deformation ratio parameters. Uniaxial tensile tests were performed on the model cornea materials as well as on corneal strips, and the results were compared to stress-strain simulations assuming the reconstructed material parameters.ResultsThe measured and simulated spatial and temporal profiles of the air puff deformation tests were in good agreement (< 7% average discrepancy). The simulated stress-strain curves of the studied hydrogel corneal materials fitted well the experimental stress-strain curves from uniaxial extensiometry, particularly in the 0–0.4 range. Equivalent Young´s moduli of the reconstructed material properties from air-puff were 0.31, 0.58 and 0.48 MPa for the three polymer materials respectively which differed < 1% from those obtained from extensiometry. The simulations of the same material but different thickness resulted in similar reconstructed material properties. The air-puff reconstructed average equivalent Young´s modulus of the porcine corneas was 1.3 MPa, within 18% of that obtained from extensiometry.ConclusionsAir puff corneal deformation imaging with inverse finite element modeling can retrieve material properties of model hydrogel polymer corneas and real corneas, which are in good correspondence with those obtained from uniaxial extensiometry, suggesting that this is a promising technique to retrieve quantitative corneal biomechanical properties.

Biomechanical Changes After In Vivo Collagen Cross-Linking With Rose Bengal–Green Light and Riboflavin-UVA

“…We have recently shown that it is possible to reconstruct corneal inherent mechanical parameters from corneal deformation imaging using inverse optimization. 6 In a recent study, Bekesi et al 22 demonstrated the validation of this technique on hydrogel model corneas and porcine corneas. Inherent material parameters were reconstructed from air puff deformation imaging and inverse optimization modeling that matched those obtained on the same samples using uniaxial extensiometry.…”

Assessment of the influence of viscoelasticity of cornea in animal ex vivo model using air‐puff optical coherence tomography and corneal hysteresis

“…CXL enabled microstructural changes of the corneas. The collagen architecture modified by CXL affects both viscous and elastic properties of the cornea although decoupling the impact of those both trends can be hard . Proper interpretation of the results of CXL experiment can be done when corneal thinning is taken into account.…”

High myopia induced by form deprivation is associated with altered corneal biomechanical properties in chicks

“…A high degree of interest in corneal biomechanics has driven the development of multiple measuring devices using various approaches. Devices for measuring corneal biomechanical properties have evolved from conventional stress-strain measuring instruments (i.e., uniaxial tensile test[ 37 ]) and inflation tests[ 38 ] to commercially available air-puff systems (i.e., Ocular Response Analyzer, ORA; Reichert, Depew, New York[ 39 ]; and Corneal Visualization Scheimpflug imaging, Corvis ST; Oculus, Wetzlar, Germany[ 40 ]); more recent devices, still under development, include optical coherence elastography (OCE)[ 41 ], Brillouin microscopy[ 42 ], ultrasound indentation[ 28 ], and corneal indentation[ 29 , 43 ]. Although the uniaxial tensile test is the gold standard in mechanical engineering, measuring corneal biomechanics using this technique is difficult, because the cornea is anisotropic, highly curved, and hydrated; furthermore, measurement along a single axis may not represent corneal biomechanics as a whole, and stretching the cornea during the measurement may disrupt the distribution of its collagen fibrils[ 44 ].…”