Non-contact Acoustic Micro-Tapping Optical Coherence Elastography (AuT-OCE) for Human Cornea

Abstract

Purpose : Understanding structural organization and function of corneal tissue is essential in providing prognosis and guiding surgical treatments. Dynamic biomechanical testing is demonstrated using a non-contact Optical Coherence Tomography (OCT) system paired with an air-coupled ultrasound transducer to quantitatively map stiffness in human corneal tissue under variable intraocular pressures (IOP).

Methods : Modern optical coherence tomography (OCT) systems can image nano-scale displacements at real-time rates, making them ideal for the mechanical imaging approach referred to as optical coherence elastography (OCE). Combining an air-coupled ultrasound transducer with phase-sensitive OCT to generate and track mechanical acoustic waves, we developed a non-contact imaging system providing high-resolution dynamic elastograms of soft tissue at near real-time imaging rates. The system captured wave propagation in cornea tissue at different IOP levels, where local displacements are calculated, and elasticity maps reconstructed based on the speed of the propagating mechanical waves. Human research cornea (n=6) were acquired and inflated to intraocular pressures of 10, 20, 30, and 40mmHg using an artificial anterior chamber. Wave velocity and displacement amplitude were used to infer relative changes in corneal elastic properties as the internal pressure increased.

Results : The AuT-OCE system detected spatially-resolved, and spatially-averaged biomechanical variations in human cornea tissue. As the IOP increased from baseline (10mmHg) to 20, 30 and 40mmHg, the mechanical wave group velocity (directly related to tissue elastic modulus, and thus stiffness) increased by 15.46% (±11.6%), 26.58% (±12.3%), and 36.63% (±10.28%), while the displacement amplitude decreased by 3.31% (±4.75%), 8.41% (±4.45%), and 11.30% (±3.6%), respectively.

Conclusions : AuT-OCE represents an efficient, dynamic, non-contact tool to study corneal biomechanics in disease (such as keratoconus) or monitor treatments (e.g., corneal crosslinking). This work used local wave speed, tissue displacement, and central corneal thickness to detect an increase in corneal stiffness at higher IOP.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

Group Velocity Maps, indicative of stiffness, for IOP (a) 10 (b) 20 (c) 30 and (d) 40 (mmHg). The center 3mm (dashed box) is used for spatial averaging (e) group velocity and (f) central corneal thickness. (g) Maximum displacement amplitude at the push (white arrow).