Optical coherence tomography and the visualization of the inner ear

Abstract

According to the World Health Organization, hearing loss affects over 1.5 billion people globally, a number suggested to rise to 2.45 billion by 2050. The large majority of hearing losses are sensorineural (SNHL) which are derived from pathologies to the inner ear organ of hearing; the cochlea. Current diagnosis of hearing loss relies on physiological techniques which provide very limited information about the type of pathologies in the cochlea. There is a need for a new diagnostic tool to better understand pathologies in human SNHL. To develop such a tool, the aim of this study is to determine the feasibility of visualizing the cochlea using Optical Coherence Tomography (OCT) on the round window (RW), an opening on the cochlea. Cochleae from sheep were fixed in 4% paraformaldehyde as the model. Two different OCT systems of varying wavelengths were tested to compare the resolution and depth penetration; the Lumedica OCT system of 840nm and a custom built 1300nm OCT system. Once OCT imaging was completed, sheep cochleae were cryosectioned, stained with histological or fluorescent stain, and imaged using bright field or fluorescent microscopy, respectively. It was found that the RW and round window membrane (RWM) was visible through both OCT systems. Using the Lumedica OCT system (short wavelength) provided images of a higher resolution and was able to image the RWM in greatest detail but compromised on penetration into the RW. The custom built 1300nm OCT system (longer wavelength) provided greater penetration into the RW and was able to identify structures 575um – 1508um into the cochlea, but compromised on the resolution of images obtained. The results acquired demonstrate that our approach to utilizing OCT on the RW is promising. Future studies will test the use of OCT for in-vivo visualization of the cochlear microstructure. This study may lead to generation of an OCT probe and could aid in visualization of the inner ear of patients with inner ear diseases.