Continuous vestibular implant stimulation partially restores eye-stabilizing reflexes.

BACKGROUND. Bilateral loss of vestibular (inner ear inertial) sensation causes chronically blurred vision during head movement, postural instability, and increased fall risk, Individuals who fail to compensate despite rehabilitation therapy have no adequate treatment options. Analogous to hearing restoration via cochlear implants, prosthetic electrical stimulation of vestibular nerve branches to encode head motion has garnered interest as a potential treatment, but prior studies in humans have not included continuous long-term stimulation or 3D binocular vestibulo-ocular reflex (VOR) oculography, without which one cannot determine whether an implant selectively stimulates the implanted ear's 3 semicircular canals. METHODS. We report binocular 3D VOR responses of 4 human subjects with ototoxic bilateral vestibular loss unilaterally implanted with a Labyrinth Devices Multichannel Vestibular Implant System vestibular implant, which provides continuous, long-term, motion-modulated prosthetic stimulation via electrodes in 3 semicircular canals. RESULTS. Initiation of prosthetic stimulation evoked nystagmus that decayed within 30 minutes. Stimulation targeting 1 canal produced 3D VOR responses approximately aligned with that canal's anatomic axis. Targeting multiple canals yielded responses aligned with a vector sum of individual responses. Over 350-812 days of continuous 24 TIM use, modulated electrical stimulation produced stable VOR responses that grew with stimulus intensity and aligned approximately with any specified 3D head rotation axis. CONCLUSION. These results demonstrate that a vestibular implant can selectively, continuously, and chronically provide artificial sensory input to all 3 implanted semicircular canals in individuals disabled by bilateral vestibular loss, driving reflexive VOR eye movements that approximately align in 3D with the head motion axis encoded by the implant.