Ultrasonic Micro-Elastography to Assess Biomechanical Properties of the Cornea.

OBJECTIVE: to both qualitatively and quantitatively investigate corneal biomechanical properties through an ultrasonic micro-elastography imaging system, which is potentially useful in diagnosis of diseases such as keratoconus, post-refractive keratectasia and tracking treatment such as cross-linking surgery.

METHODS: our imaging system has a dual frequency configuration, including a 4.5 MHz ring transducer to push the tissue and a confocally aligned 40 MHz needle transducer to track micron-level displacement. 2D/3D acoustic radiation force impulse (ARFI) imaging and the Young's modulus in the region of interest were performed on ex vivo porcine corneas that were either cross-linked using formalin solution or preloaded with IOPs from 5 mmHg to 30 mmHg.

RESULTS: the increase of corneal stiffness and the change in cross-linked volume following formalin crosslinking could be precisely observed in the ARFI images and reflected by the reconstructed Young's modulus while the B-mode structural images remained almost unchanged. In addition, the relationship between the stiffness of the cornea and IOPs was investigated among twelve porcine corneas. The corneal stiffness is significantly different at various IOPs and has a tendency to become stiffer with increasing IOP.

CONCLUSION: Our results demonstrate the principle of using ultrasonic micro-elastography techniques to image the biomechanical properties of the cornea. Integrating high-resolution ARFI imaging labelled with reconstructed Young's modulus and structural imaging of the cornea can potentially lead to a routinely performed imaging modality in the field of ophthalmology.