Heartbeat optical coherence elastography: corneal biomechanics in vivo

Abstract

. Significance: Mechanical assessment of the cornea can provide important structural and functional information regarding its health. Current clinically available tools are limited in their efficacy at measuring corneal mechanical properties. Elastography allows for the direct estimation of mechanical properties of tissues in vivo but is generally performed using external excitation force. Aim: To show that heartbeat optical coherence elastography (Hb-OCE) can be used to assess the mechanical properties of the cornea in vivo. Approach: Hb-OCE was utilized to detect Hb-induced deformations in the rabbit cornea in vivo without the need for external excitation. Furthermore, we demonstrate how this technique can distinguish corneal stiffness between untreated (UT) and crosslinked (CXL) tissue. Results: Our results demonstrate that stiffness changes in the cornea can be detected using only the Hb-induced deformations in the cornea. Additionally, we demonstrate a statistically significant difference in strain between the UT and CXL corneas. Conclusions: Hb-OCE may be an effective tool for assessing the mechanical properties of the cornea in vivo without the need for external excitation. This tool may be effective for clinical assessment of corneal mechanical properties because it only requires optical coherence tomography imaging and data processing.

Temporal phase evolution OCT for measurement of tissue deformation in the human retina in-vivo

“…Non-invasive OCE measurements are however still challenging in the eye and have essentially been limited to the cornea in human subjects in-vivo [ 24 ]. Compared to standard OCE which uses an external pulse source, our method relies on the natural cardiac pulsation to investigate tissue deformation, similarly to recent work reported on passive elastography in the cornea in humans [ 37 ] and in animal models [ 36 ]. While such method does not provide information on the elastic modulus (the force exerted on the tissue is unknown), it gives interesting insights on retinal tissue motion over the range of several seconds.…”

“…While such method does not provide information on the elastic modulus (the force exerted on the tissue is unknown), it gives interesting insights on retinal tissue motion over the range of several seconds. In a further step, strain estimation could be performed based either on the LSM [ 18 ], as in heartbeat OCT [ 36 ], or the VM [ 19 ] and optimized VM [ 20 , 21 ].…”

“…In the second method (M2), the phase difference between consecutive B-scans is calculated followed by temporal integration relative to an initial reference frame. This second method has been used for example, in OCE and FF-OCT [ 36 , 38 ]. If phase unwrapping is performed for the data provided by M1, both methods are mathematically equivalent [ 53 ], however, each of them has slight advantages for some specific data presentation schemes, so we will demonstrate results obtained with both of them (in the majority of the presented results, we used M1).…”

“…Passive excitation can result from the cardiac beatings or muscle contractions, among other examples. In-vivo OCT investigations in animal models have already shown the potential of the method for the evaluation of both corneal stiffness [ 35 ] and corneal tissue response [ 36 ] under natural pulsatile motion. While the first study focuses on the analysis of mechanical shear wave propagation, the second study is based on the calculation of tissue deformation and strain using the LSM over time.…”

Enhanced medical diagnosis for dOCTors: a perspective of optical coherence tomography

“…Only a month later, Nair et al 305 gave another indication for the feasibility of non-contact heartbeat ophthalmic OCE in an ex vivo porcine eye model with controlled intraocular pressure changes. In January 2021, Nair et al 307 achieved heartbeat OCE in an in vivo rabbit model, but the method was not completely non-contact as a glass imaging window was used to minimize bulk motion. The heart pulse compressed the corneal tissue against this imaging window, resulting in the desired displacement.…”