Monday  |  Lakeshore B  |  11:40 AM–12:00 PM

#19433, Characterization of the Viscoelastic Properties and Anisotropy of Corneal Tissue based on Optical Coherence Elastography

Glaucoma is one of the leading causes of vision loss and blindness affecting millions worldwide. It is closely linked to risk factors like elevated intraocular pressure (IOP) and reduced corneal hysteresis. However, accurately measuring IOP in a reliable, non-invasive manner remains a significant challenge, limiting the precision of glaucoma diagnosis and the effectiveness of intervention therapies. The cornea is a complex, layered material exhibiting both viscoelastic and anisotropic properties whose mechanical behavior is largely governed by its five-layered structure, primarily dominated by the stroma. Elastic wave propagation methods are ideal for non-destructive characterization of anisotropic and viscoelastic properties. The cornea’s plate-like geometry is well-suited for analysis using guided elastic waves, or Lamb waves. Optical coherence elastography (OCE) recently emerged as a promising, non-destructive, and non-invasive tool for the measurement of Lamb wave propagation in biological materials including the cornea. Previous efforts to model the cornea's mechanical behavior have either focused on its anisotropy or viscoelasticity, with taking both into consideration. In this study we use OCE to measure the frequency-dependent wave speed and attenuation of Lamb waves in porcine corneas. We observe that increasing IOP increases the phase velocity of the A0 waves while the amplitude decay coefficient decreases, as expected for a polymer that stiffens while viscous dissipation effects decrease with applied stretch. We also measure the wave speed as a function of the polar angle and observe that it depends on this angle outside the plane of isotropy. We propose a modified NITI model in which the shear portion of the stiffness tensor follows an orthotropic model, the longitudinal portion is assumed to be isotropic, and the shear constants are assumed to be complex-valued to account for viscoelasticity. We employ a finite element (FE) numerical model to calculate the wave speed and decay coefficient, using the frequency-dependent shear constants as model input parameters and estimate the out-of-plane shear storage and loss moduli by fitting the numerical model to the measurement. This approach incorporates the effects of anisotropy and linear viscoelasticity and can provide a precise framework for inverse analysis of OCE measurements for accurate mechanical characterization of cornea tissues.

Evan Dieppa   Northwestern University
Ziwei Wang   Northwestern University
Oluwaseyi Balogun   Northwestern University