The effects of curvature and thickness of cornea-based structures assessed by finite element modeling and optical coherence elastography Zhaolong Han, Jiasong Li, Manmohan Singh, Salavat R. Aglyamov, Chen Wu, Chih-hao Liu, and Kirill V. Larin Department of Biomedical Engineering, University of Houston

Outline Introduction Methods Results Conclusion

Introduction One approach for extracting the biomechanical properties of the cornea is by assessing the propagation of an elastic wave by Optical Coherence Elastography (OCE). However, the wave models currently used to quantify the biomechanical properties are based on the assumption of a thin plate in half-space, which does not incorporate the effects of the thickness and curvature of the cornea. We have performed finite element (FE) simulations combined with OCE experiments in order to understand the influence of the corneal curvature and thickness on the group velocity of an elastic wave.

Methods: OCE setup OCE set up J. Li, et al, "Dynamic optical coherence tomography measurements of elastic wave propagation in tissue-mimicking phantoms and mouse cornea in vivo," J Biomed Opt 18(12), (2013).

Methods: cornea-shape samples Contact lens Alcon Inc., TX, USA; 67% delefilcon A, 33% water Phantom strip on a water balloon

Methods: FEM models FEM model Excitation Four types of cornea-like structures

Results: radius effect Both FEM and OCE experiments demonstrate that group velocity decreases as radius of curvature increases.

Results: thickness effect Both FEM and OCE experiments demonstrate that group velocity increases with thickness.

Results: FEM displacement map Different FEM simulated displacement contour maps (2D and 3D views) at t=3.2 ms for different cornea-shape under the same Young’s modulus E=60kPa.

Results: FEM displacements FEM simulated vertical displacement temporal profiles obtained at 0.16 mm, 0.80 mm, 1.44 mm and 2.08 mm away from the central excitation for the four types of structures.

Conclusions In cornea-shape structure, the group velocity decreases as the radius of curvature increases, and that the velocity increases as the thickness of the sample increases. The curvature and thickness must be considered when improving wave models used for reconstructing the biomechanical properties of the cornea from OCE measurements. Combining OCE with FEM is a promising method to quantitatively reconstruct elasticity in cornea.

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