Heartbeat Optical Coherence Elastography: Utilizing Heartbeat to Measure Corneal Biomechanical Properties
Achuth Nair1, Manmohan Singh1, Salavat R. Aglyamov2, and Kirill V. Larin1,3,*
1. Department of Biomedical Engineering, University of Houston
2. Department of Mechanical Engineering, University of Houston
3. Department of Molecular Physiology and Biophysics, Baylor College of Medicine
Abstract
Corneal pathologies such as keratoconus and post-surgical ectasia can lead to tissue damage and alter corneal biomechanical properties. An established method to directly assess the mechanical properties of biological tissues is elastography. Typically, elastography uses external excitation to induce deformation in the tissue. However, passive methods of elastography are currently being investigated, where deformation induced by physiological sources are analyzed to assess biomechanical properties. Here we describe the in vivo application of heartbeat optical coherence elastography (Hb-OCE). This elastography technique is used to assess the mechanical properties of the in vivo rabbit cornea using deformation caused by the heartbeat induced ocular pulse. Qualitative measure of stiffness is obtained, and corneal stiffness is distinguished between untreated control cornea and a collagen crosslinked cornea. An SD-OCE system in the common-path configuration is used to acquire images of the apex of the cornea of an anesthetized rabbit. The rabbit heartbeat is acquired using a pressure transducer applied externally to the rabbit’s chest. A rabbit with an untreated cornea was initially measured, followed by a rabbit that had its cornea crosslinked. For both measurements, a rebound tonometer detected an intraocular pressure (IOP) of approximately 10 mmHg. OCT images are synchronized to heartbeat measurements in a post processing step. Motion during the ocular pulse is detected, and the displacement in the cornea is measured. This displacement is then translated to axial strain, and the strain is compared between the untreated and crosslinked corneas. Displacement and strain in the untreated sample is significantly greater over the entire measurement period. Average strain measured over heart cycles was compared, and the results showed a significant difference in strain between tissue types. This study suggests that Hb-OCE is feasible for assessing the biomechanical properties of the cornea and can distinguish a crosslinked cornea from an untreated one. Currently, measurement is performed by direct contact, but non-contact measurements are an area of investigation. Furthermore, our technique is currently limited to qualitative assessment of strain, but quantitative assessment is an important area of development.
Speaker
Achuth Nair
University of Houston
United States
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