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Review Article

Revealing the morphology and function of the and middle ear with optical coherence tomography

George W. S. Burwood1, Anders Fridberger1,2, Ruikang K. Wang3, Alfred L. Nuttall1

1Department of Otolaryngology, Oregon Research Center/HNS, Oregon Health & Science University, Portland, OR, USA; 2Department of Clinical and Experimental Medicine, Section for Neurobiology, Linköping University, Linköping, Sweden; 3Department of Bioengineering and Department of Ophthalmology, University of Washington, Seattle, WA, USA

Correspondence to: Alfred L. Nuttall. Oregon Hearing Research Center, Department of Otolaryngology-Head & Neck Surgery, Oregon Health & Science University, Portland, OR, USA. Email: [email protected].

Abstract: Optical coherence tomography (OCT) has revolutionized physiological studies of the hearing organ, the vibration and morphology of which can now be measured without opening the surrounding bone. In this review, we provide an overview of OCT as used in the otological research, describing advances and different techniques in vibrometry, angiography, and structural imaging.

Keywords: Cochlea; cochlear mechanics; imaging; optical coherence tomography (OCT); organ of Corti (OoC); otology

Submitted Feb 16, 2019. Accepted for publication May 09, 2019. doi: 10.21037/qims.2019.05.10 View this article at: http://dx.doi.org/10.21037/qims.2019.05.10

Introduction is coupled via the membrane to the fluid filled, three chambered cochlea (Figure 1C,D). A pressure The exquisite sensitivity and frequency discrimination difference in the fluid, across these chambers, induced by capacity of the mammalian auditory system gives a strong stapes vibration, causes a travelling wave of motion that survival advantage to many species which rely on cues from propagates along the collagenous (BM), their acoustic environment. Researchers in probe peaking at different locations depending upon the frequency the to understand its basic mechanisms, and in of the acoustic stimulus (2). High frequency travelling order to learn more about its evolutionary development (1). waves peak closer to the base of the cochlea, and low From a clinical point of view, peripheral hearing loss is a frequency travelling waves peak closer to the apex. Termed significant public health issue, and the better understanding tonotopicity, this frequency distribution arises in part from of the function of the hearing organ would lead to improved the passive mechanical properties of the BM, i.e., from its prevention and treatment of a variety of ailments. Optical mass and stiffness, which vary as a function of place in the coherence tomography (OCT) has contributed substantially cochlea (3-7). to physiological studies of the inner ear and appears poised The hearing organ itself is the organ of Corti (OoC) to also have a strong influence on clinical diagnosis of (Figure 1E,F). This consists of two types of sensory cell, hearing disorders. outer and inner hair cells, and assorted supporting cells, The peripheral pathway functions as follows, and a sandwiched between two structures, the BM and tectorial summary of the anatomy can be seen in Figure 1. The membrane (TM). Outer hair cells (OHCs) detect the cochlea is a bony structure found bilaterally in the temporal relative shear displacement of the BM and TM (8), bone of the skull (Figure 1A). Briefly, sound impinging on converting the kinetic energy of that displacement into the tympanum elicits vibration of a chain of three bones, the transverse force. Inner hair cells (IHCs) detect the velocity auditory (Figure 1B). The third ossicle, the stapes, of the surrounding fluid in the subtectoria