Shear wave elastography of ex vivo human corneas using phase-sensitive optical coherence tomography

Assessing the biomechanical properties of the cornea can provide clinically valuable information in addition to structural images for better management of pathologies (e.g. glaucoma) or refractive surgeries. OCT provides a micron scale and high sensitivity that are ideal for ophthalmic applications. We propose a shear wave elastography (SWE) method for the cornea based on phase-sensitive optical coherence tomography (PhS-OCT). SWE consists in launching a propagating shear wave in tissues and retrieving tissue elasticity from the shear wave speed. We used a piezo-electric actuator in contact with the cornea to induce shear waves that were then tracked using a PhSOCT system operating in M-B mode at an equivalent frame rate of 45 kHz. The actuator was driven by a broadband, linear-swept frequency sine. The corresponding displacements were numerically transformed into a short and spatially localized pulse by a pulse compression algorithm. The local shear wave speed was then computed using time-of-flight estimations. We performed experiments on excised human corneas obtained from the eye bank. The corneas were mounted on an artificial anterior chamber in which the IOP could be varied. Elasticity measurements were acquired for IOP ranging from 10 to 40 mmHg. These preliminary studies demonstrate the feasibility of using PhS-OCT for elastography of human corneas. Further studies will aim at developing non-contact shear sources for clinical translation.