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Behrouz Tavakol, Judith Birkenfeld, Antoine Ramier, Seok-Hyun (Andy) Yun; Development of a time-domain finite-element model of acoustic wave propagation in the cornea. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1401.
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Upon mechanical stimuli, such as air-puff, mechanical waves are generated and propagate in the cornea. These acoustic waves can be described as planar Lamb waves or Rayleigh surface waves, depending on their acoustic wavelengths compared to corneal thickness. Rayleigh waves propagate along the epithelial surface with speeds mainly related to the shear modulus of the corneal tissue, independent of the corneal thickness. Therefore, measuring Rayleigh wave speeds is a promising way of estimating the corneal elasticity. Here we introduce a finite-element model to assess the effect of individual parameters on the corneal wave propagations to better generate and detect Rayleigh waves.
We used COMSOL to simulate acoustic wave propagation. We first verified the method for a simple plate model of the cornea. We then developed a more complete model of eyeball consisting of cornea, limbus, sclera, and aqueous and vitreous humors. The model considers the solid-fluid interaction between solid tissues and liquids, the viscoelasticity of solid components, the viscosity of aqueous and vitreous humors, and the intraocular pressure. We varied different parameters and observed the wave propagation on the corneal surface.
Simulation results from the flat cornea model agreed with the theory of elastic plates. This simple model was also used to verify different boundary conditions and the effect of fluid domain under the cornea on the wave propagation. The model produced time sequence of the excitation of mechanical vibrations and propagation of acoustic waves. The typical temporal resolution was 1/20th of the acoustic period. The time domain method allows us to investigate transient and time-varying evolution of acoustic waves. Among 40 cycles simulated for each condition, the first few cycles showed how the wave propagates through cornea and other components, while the last few cycles were picked for data analysis to obtain different wave properties. The transient responses depend on the duration, width, and types of excitation sources.
We have developed a model to simulate wave propagations in the cornea. Using this model, we have investigated the effect of various mechanical and anatomical parameters on the wave propagations in the cornea. This tool will be useful to design devices to generate optimal mechanical stimulus and to interpret experimental data of corneal elastography.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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