Heartbeat OCE: corneal biomechanical response to simulated heartbeat pulsation measured by optical coherence elastography

Abstract

Significance: It is generally agreed that the corneal mechanical properties are strongly linked to many eye diseases and could be used to assess disease progression and response to therapies. Elastography is the most notable method of assessing corneal mechanical properties, but it generally requires some type of external excitation to induce a measurable displacement in the tissue.

Aim: We present Heartbeat Optical Coherence Elastography (Hb-OCE), a truly passive method that can measure the elasticity of the cornea based on intrinsic corneal displacements induced by the heartbeat.

Approach: Hb-OCE measurements were performed in untreated and UV-A/riboflavin cross-linked porcine corneas ex vivo, and a distinct difference in strain was detected. Furthermore, a partially cross-linked cornea was also assessed, and the treated and untreated areas were similarly distinguished.

Results: Our results suggest that Hb-OCE can spatially map displacements in the cornea induced by small fluctuations in intraocular pressure, similar to what is induced by the heartbeat.

Conclusions: The described technique opens the possibility for completely passive and noncontact in vivo assessment of corneal stiffness.

Keywords: cornea; optical coherence elastography; optical coherence tomography; pulsation; tissue biomechanics.

Fig. 1

OCE system schematic. A closed-loop IOP controller-induced sinusoidal fluctuations in IOP. Induced displacements were measured with an SD-OCT system.

Fig. 2

Corneal instantaneous displacement in the typical untreated and crosslinked corneas during infusion (IOP ↑, $\sim 2\mathrm{s}$ after the pulse starts) and withdrawal (IOP ↓, $\sim 6\mathrm{s}$ after the pulse starts) of the fluid from the eye-globe.

Fig. 3

Cumulative strain for a typical untreated and CXL cornea. IOP over time is shown as well. Dotted lines represent points in time where corresponding displacement was mapped in Fig. 2.

Fig. 4

(a) Structural OCT image of a partially CXL porcine cornea, where the left side was CXL treated and the right side was untreated (UT). (b) Cumulative strain for the UT and CXL regions of the cornea are shown with IOP over time.

Fig. 5

(a) Cumulative strain ($\text{mean}\pm \text{standard deviation}$ of all samples, $N=3$ for each group). (b) Summary of sample stiffness (mean standard deviation of all samples) for untreated and crosslinked corneas. Results from a two-sample $t$-test are shown.