Finite Element Modelling of Corneal Biomechanics Assessment Using Ultrasonic Elastography

Abstract

Corneal diseases affect corneal tissue shape and its biomechanics leading to a degradation ofthe overall vision quality. Refractive surgeries restore corneal refractive power. However, its outcomes arehighly dependent on corneal biomechanics pre-surgery while changing corneal biomechanics post-surgery.Cornea behavior is obtained by estimation of corneal biomechanics pre- and post-refractive surgeries eitherex- or in-vivo. Demand for non-invasive in-vivo measurement is highly recommended as it preserves bothcorneal shape and structure on contrary to invasive ex-vivo methods. Until now no clinically reported in-vivodevice offering corneal biomechanics spatial distribution exists. In this research, ultrasonic noninvasive invivomeasurement for estimating corneal biomechanics using FEM simulation is proposed. Eleven differentelastic moduli FEMs are used to cover the range of elasticity of human cornea in normal and pathogenicstatus. Two ultrasonic tissue deformation measurement methods are used in this study. Namely, the radialShear Wave Speed (rSWS) and Focal Peak Axial Deformation (FPAD). rSWS utilizes two B-mode framerates; 10kHz and 100KHz typically. FPAD uses 100KHz for tissue deformation data collection. Twomathematical formulae for prediction of non-involved data points are power formula and logarithmic formulaare used. Simulation results shown that rSWS is efficient for high frame rate transducer. Accuracy of99.8%±2.4% is achieved with 100KHz while for 10KHz the accuracy is 95.5%±29%. Results shown also,that accuracy at 100KHz is nearly stable on contrary to highly fluctuating accuracy at 10KHz. FPAD shownthat logarithmic formula is optimum with Mean Square Error (MSE) of 0.006, compared to MSE of 0.09 forpower formula. FPAD has an advantage over rSWS to be implemented with low frame rate transducers whilerSWS has the advantage of quantitative measurement. Maximum temperature rise of 0.9 C is achieved dueto the ARFI where this value is under the FDA regulation.