Multimodal Heartbeat and Compression Optical Coherence Elastography for Mapping Corneal Biomechanics

Abstract

The biomechanical properties of the cornea have a profound influence on the health, structural integrity, and function of the eye. Understanding these properties may be critical for diagnosis and identifying disease pathogenesis. This work demonstrates how two different elastography techniques can be combined for a multimodal approach to measuring corneal biomechanical properties. Heartbeat optical coherence elastography (Hb-OCE) and compression OCE were performed simultaneously to measure the stiffness of the cornea in an in vivo rabbit model. Measurements were further performed after collagen crosslinking to demonstrate how the combined technique can be used to measure changes in corneal stiffness and map mechanical contrast. The results of this work further suggest that measurements from Hb-OCE and compression OCE are comparable, meaning that Hb-OCE and compression OCE may be used interchangeably despite distinct differences in both techniques.

Keywords: biomechanics; cornea; elasticity; optical coherence elastography (OCE); optical coherence tomography (OCT).

FIGURE 1

(A) Schematic of the combined Hb+Compression OCE system. (B) Zoomed in view of the interface between the reference glass and cornea with visualization of the forces acting on the cornea. The blue arrow indicates the compression force applied by the piezoelectric transducer (PZT), and the red arrows illustrate the force applied by the hearbeat-induced ocular pulse. (C) PZT actuation as a function of image acquisition, where each B-scan took 16 ms. Hb-OCE data was acquired between two images of the same state (i.e., B-scan 0 versus B-scan 2), and compression OCE measurements were acquired between images of opposite states (i.e., B-scan 0 versus B-scan 1).

FIGURE 2

(A) OCT intensity B-scan of a representative virgin cornea. Corneal stiffness mapped by (B) Hb-OCE and (C) compression OCE. (D) Box and whisker plot comparing measurements performed by Hb-OCE and compression OCE (n = 7). The box shows median and upper and lower quartiles, and the whiskers represent the minimum and maximum data points. Scale bars indicate 100 μm.

FIGURE 3

(A) OCT intensity B-scan of the cornea in Figure 2 that has been crosslinked. Corneal stiffness mapped by (B) Hb-OCE and (C) compression OCE (D) Mean and standard deviation of virgin and crosslinked corneas measured by Hb-OCE and compression OCE. Scale bars are 100 μm.

FIGURE 4

(A) OCT intensity B-scan of a partially crosslinked cornea. The dotted boxes indicate the (red) crosslinked and (blue) virgin regions, respectively. Corneal stiffness mapped by (B) Hb-OCE and (C) compression OCE. (D) Mean and standard deviation of virgin and crosslinked regions measured by Hb-OCE and compression OCE. Scale bars are 100 μm.