Treating Deafness with Better Vision: Cellular-Level Optical Imaging of the Inner Ear

Sensorineural hearing loss is the most common type of hearing loss worldwide, yet the underlying cause is typically unknown because the inner ear cannot be biopsied today without destroying hearing, and intracochlear cells have not been imaged with resolution sufficient to establish diagnosis. Intracochlear imaging has been technologically challenging because of the cochlea’s small size and encasement in bone. Here we report the imaging of the mouse cochlea in situ without exogenous dyes, through a membranous round window, using near-infrared femtosecond laser as the excitation mechanism and endogenous two-photon excitation fluorescence (TPEF) and second harmonic generation (SHG) as the contrast mechanisms. We find that TPEF exhibits strong contrast, allowing cellular, and even subcellular, resolution and detection of specific, noise-induced pathologic changes.

Our results demonstrate that the round window provides useful access to the cochlea through the middle ear, and they motivate future development of a new and efficient diagnostic tool based on two-photon micro-endoscopy that may allow us to establish precise diagnoses for deafness, paving the way to reversal. The optical tools we are developing could facilitate safer insertion of existing and emerging devices for therapy and continuous monitoring. For example, in separate research published last autumn, we developed an energy harvester that makes use of endocochlear potential, a battery-like electrochemical gradient found in and actively maintained by the inner ear, which could power various sensors in the inner ear and its vicinity. The presentation will include imaging of a mouse cochlea, the size of which matches Lincoln’s ear on a penny.