Opto-Acoustic Selective Mechanical Stimulation of the Vestibular System

Abstract

An implantable vestibular prosthesis system includes an implantable optical array of optical sources configured for engagement with a disordered vestibular system to deliver optical stimulation signals to target stimulation locations within the bony or membranous labyrinth of the disordered vestibular system. An implantable stimulation processor is connected to the optical array and configured to produce the optical stimulation signals with the optical sources so as to generate directional pressure waves within the endolymphatic fluid directed to the target stimulation locations for vestibular perception by residual vestibular functioning.

Claims

1. An implantable vestibular prosthesis system comprising: an implantable optical array including a plurality of optical sources configured for engagement with a disordered vestibular system to deliver optical stimulation signals to one or more target stimulation locations within the bony or membranous labyrinth of the disordered vestibular system; and an implantable stimulation processor connected to the optical array and configured to generate directional pressure waves within endolymphatic fluid, based on the optical stimulation signals delivered to the one or more target stimulation locations from the optical sources in order to mechanically stimulate the disordered vestibular system.

2. The system according to claim 1, wherein the optical array is configured for placement against an outer surface of vestibular bone to deliver the optical stimulation signals by optical transmission through the vestibular bone.

3. The system according to claim 1, wherein the optical array is configured for placement within a perilymphatic space outside the membraneous labyrinth.

4. The system according to claim 1, wherein the optical array is configured for placement within the membraneous labyrinth without mixing perilymph and endolymph.

5. The system according to claim 1, wherein the one or more target stimulation locations include stereocilia of the disordered vestibular system.

6. The system according to claim 1, wherein the one or more target stimulation locations are within a semi-circular canal of the disordered vestibular system.

7. The system according to claim 1, wherein the one or more target stimulation locations are within the utricle of the disordered vestibular system.

8. The system according to claim 1, wherein the one or more target stimulation locations are within the saccule of the disordered vestibular system.

9. The system according to claim 1, wherein the optical array is a linear array of optical sources.

10. The system according to claim 1, wherein the optical array is a two dimensional array of optical sources.

11. The system according to claim 1, wherein the optical array is a circular array of optical sources.

12. The system according to claim 1, wherein the optical stimulation signals include optical pulses.

13. A method of vestibular stimulation comprising: providing an implantable optical array including a plurality of optical sources engaged with a disordered vestibular system to deliver optical stimulation signals to one or more target stimulation locations within the bony or membranous labyrinth of the disordered vestibular system; producing sequences of optical stimulation signals with the plurality of optical sources; and generating directional pressure waves within endolymphatic fluid, based on the optical stimulation signals delivered to the one or more target stimulation locations, in order to mechanically stimulate the disordered vestibular system.

14. The method according to claim 13, wherein the optical array is engaged against an outer surface of vestibular bone, and wherein the optical stimulation signals are delivered by optical transmission through the vestibular bone.

15. The method according to claim 13, wherein the optical array is engaged within a perilymphatic space outside the membraneous labyrinth.

16. The method according to claim 13, wherein the optical array is engaged within the membraneous labyrinth without mixing perilymph and endolymph.

17. The method according to claim 13, wherein the one or more target stimulation locations include stereocilia of the disordered vestibular system.

18. The method according to claim 13, wherein the one or more target stimulation locations are within a semi-circular canal of the disordered vestibular system.

19. The method according to claim 13, wherein the one or more target stimulation locations are within a utricle of the disordered vestibular system.

20. The method according to claim 13, wherein the one or more target stimulation locations are within a saccule of the disordered vestibular system.

21. The method according to claim 13, wherein the optical array is a linear array of optical sources.

22. The method according to claim 13, wherein the optical array is a two dimensional array of optical sources.

23. The method according to claim 13, wherein the optical array is a circular array of optical sources.

24. The method according to claim 13, wherein the optical stimulation signal include optical pulses.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 shows anatomical detail of a human ear implanted with a vestibular implant system.

[0014] FIG. 2 shows a side cross-sectional view of an opto-acoustic vestibular stimulation electrode according to an embodiment of the present invention.

[0015] FIG. 3 shows principles of a circular array according to an embodiment of the present invention.

[0016] FIG. 4 shows principles of a two dimensional array according to an embodiment of the present invention.

[0017] FIG. 5 shows locations at the vestibular system for placement of the implantable optical array according to an embodiment of the invention.

DETAILED DESCRIPTION

[0018] Embodiments of the present invention are directed to an atraumatic mechanical vestibular stimulator with no moving parts, which can be used non-invasively and can selectively stimulate the macular organs using the optoacoustic effect that arises from optical stimulation. Optical stimulation with multiple optical sources using short focused pulses at a specific rate, energy and peak power can heat the target tissue so that the expansion due to the heat (overcoming thermal-stress confinement) generates a pressure wave. Such a pressure wave, like with electrical current spread, is omnidirectional from the source and can be used to mechanically stimulate sensory epithelium in the vestibular system. Such systems can be beneficial for patients having partial vestibular disorders with some residual hair cells and stereocilia.

[0019] For effective mechanical stimulation of the endolymphatic fluids within the membranous labyrinth with existing approaches (see, e.g., U.S. Pat. No. 7,488,341 and U.S. Patent Publication 2007/0100263) imply an opening into the vestibular interior in order to directly stimulate the membranous labyrinth. By contrast, optical sources can be placed outside the vestibular canal, and provided that the bone is thin enough (either natural or with careful surgical preparation to preserve the integrity of the canal), the optical stimulation signals can be delivered via optical transmission through the bone to locations within the bony or membranous labyrinth of a partially disordered vestibular system to generate a directional pressure wave within the endolymphatic fluid for vestibular perception via residual vestibular functioning. In case of thicker bone the stimulation location may be for example within the bony labyrinth. In this case the directional pressure wave directly generated by the optical stimulation signal is within the perilymphatic fluid. This pressure wave deflects the soft membrane tissue between bony and membranous labyrinth that in turn displaces endolymphatic fluid such that a directional pressure wave in the endolymphatic fluid is indirectly generated. This new non-invasive stimulation solution needs no moving parts, in contrast to existing non-invasive ideas where the actuator acts directly on the endosteum with the risk of rupturing the membrane and consequent loss in residual function.

[0020] For example, an implantable vestibular prosthesis system and method can be implemented in an implantable vestibular stimulator 114 as shown in FIG. 1 that provides by a stimulation processor control signals to the optical sources 115 on an implantable array that is configured for placement in a multitude of possible locations including: against or outside of an outer surface of vestibular bone outside of the fluidic spaces, for example where the bone is thin enough to allow light to shine through; against or within the inner surface of the vestibular bone within the perilymphatic space but not within the membranous labyrinth; within the membranous endolymphatic fluid spaces without causing damage resulting in the mixing of the perilymph and endolymph fluids, and the optical sources 115 are configured to deliver optical stimulation signals via optical transmission through the vestibular bone and/or vestibular fluids, i.e. endolymphatic or perilymphatic fluids, to stimulation locations in the membranous or bony labyrinth of a partially disordered vestibular system to generate a directional pressure wave within the endolymphatic fluid for vestibular perception via residual vestibular functioning, for example in the semi-circular canals (106, 107, 108) and/or otolith organs 116. Some exemplary locations are shown in FIG. 5 and numbered from 1 to 3. In one embodiment, an optical signal generation process (e.g., a software process running on a stimulation processor within the vestibular stimulator 114) controls the optical sources 115 to produce the optical stimulation signals as sequences of optical pulses to generate directional pressure waves in the vestibular fluid that are directed to one or more target sensory epithelium locations within the disordered vestibular system for vestibular perception via residual vestibular functioning. In one embodiment the optical sources 115 may include converging lenses so as to focus the optical stimulation signal within the bony or membranous labyrinth, for example within the perilymphatic or endolymphatic fluid.

[0021] Stimulation with a single optical source would achieve the same omnidirectional result as with prior mechanical systems. However, if multiple optical sources 202 are placed in an optical array 201 as shown in FIG. 2, then the optical stimulation signals 204 can be delivered through the vestibular bone 203 and the perilymph 205 to target locations 207 within the endolymph 206 and stimulated sequentially over time in a specified direction. Once the first optical source 202 is stimulated, a first omnidirectional pressure wave is generated at the target location 207 within the endolymph 206. As the initial pressure wave passes the second target location 207 of the second optical source 202, then the second optical source 202 is stimulated and a second pressure wave is generated that sums with the first pressure wave so that the summing of the resulting pressure waves in the direction of sequential stimulation encourages the endolymph 206 to move in that direction towards the target stereocilia 208 to cause them to deflect and generate neural signals to the vestibular nerve 209. Focusing of the optical stimulation signals 204 at the target locations 207 can be enhanced by using focusing lenses, which would focus the energy at the target location, i.e. the optical stimulation signal heats up and expands the fluid only in the area of focus and allows for better control of pressure wave generation, allowing for a higher resolution of target locations. In addition, focusing the optical stimulation signals 204 at the target locations 207 may reduce the energy required for driving the optical source 202 to generate the same desired magnitude of the pressure wave as that without focusing. Although the target locations 207 are shown in the membranous labyrinth, it is understood and as described before, that they may be within the perilymph 205 in the bony labyrinth.

[0022] Such arrangements allow a more distant placement of the optical array 201 from the target stereocilia 208, while providing direction-specific stimulation. This differs from other existing approaches that employ direct optical stimulation where attempting such directionality would pose greater risks of implantation trauma and would be prone to failure because of the many moving parts.

[0023] Selectivity is also an issue with regards to the utricle and saccule. In the case of electrical stimulation, given enough power, electrical current spread will stimulate any neuron in the vicinity regardless of the direction of current spread movement. Conversely, in the case of mechanical stimulation, it is the hair cells that respond to the stimulus, and hair cells and their stereocilia are typically organized and aligned in a particular way such that they are sensitive to movement in a particular plane and direction. For example, in the ampulla of a semi-circular canal, all the hair cells are aligned so that they are only sensitive to movement in the plane of that canal. In that case, one stimulation source would be enough (as with electrical stimulation), assuming that the stimulus signal does not extend to other ampulla. In the case of the utricle and saccule however, the hair cells and stereocilia are arranged in a multidirectional pattern such that their sensitivity to direction varies with position (as indicated by the arrows in FIG. 3). In that case, placing a single stimulation source in an arbitrary position will generate a pressure wave that approaches the hair cells and stereocilia, but only those hair cells and stereocilia aligned in that direction will elicit a stimulus in the nerve. Due to the multidirectional alignment organization of the hair cells and stereocilia, this one single stimulation source lacks directionality. Instead, an array of multiple stimulation sources can be used in order to control which hair cells should respond (corresponding to the movement of the head). In that case, one or more sources would be stimulated simultaneously and/or sequentially in order to achieve the desired net direction and amplitude of movement of the vestibular fluid due to the pressure wave, and consequently deflecting the target stereocilia that are aligned in that specific direction.

[0024] Such a multi-source array could be placed either within the membranous labyrinth (invasive), in the perilymphatic space, or outside of the vestibule altogether (both non-invasive), provided that the bone in between the optical sources and the target locations is thin enough to allow enough light to pass through. As described before, the optical sources may include converging lenses so as to focus the optical stimulation signal within the bony or membranous labyrinth, for example within the perilymphatic or endolymphatic fluid.

[0025] FIG. 3 shows an example of a linear array of multiple optical sources 301 arranged circularly around a macular organ 302. In such an array, the pressure wave summation effects would result in multiple desired directions being simultaneously excited. By contrast, a two dimensional array of optical sources 401 as shown in FIG. 4, would produce pressure wave summation effects resulting in directionality in a single direction as shown in FIG. 2.

[0026] In specific embodiments, the optical sources may specifically be a vertical-cavity surface-emitting lasers (VCSELs), LEDs, or optical fibers. In the case of VCSELs, sequential stimulation avoids overuse of the VCSELs and so reduces the risk of overheating and failure. Sequential VCSEL stimulation also suggests reduced power requirements per VCSEL, which then further suggests that smaller size VCSELs could be used, with less heat produced, and so reduced cooling time needed.

[0027] It will be understood that for placement of the optical sources on the surface of vestibular bone, that bone needs to be thin enough to allow enough light to pass through. Embodiments will be useful only when hair cells and stereocilia retain at least some residual vestibular function, so only patients with partial vestibular loss may benefit. The optical sources may lose efficiency over time and their output levels may be monitored and the control signal adjusted accordingly.

[0028] In the foregoing, references to vestibular implant systems should be understood broadly to include all implantable arrangements that provide stimulation signals affecting the balance sensing system. Specifically such arrangements may or may not include motion sensors, whether internal or external. For example, a vestibular implant system without motion sensing signals may be useful for treatment related to Meniere's disease and may be thought of as a Meniere's implant. And vestibular implant arrangements may also be integrated together with other related implantable systems such as middle ear implants, cochlear implants, bone conduction implants, auditory brainstem implants, etc.

[0029] Although various exemplary embodiments of the invention have been disclosed, it should be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of the invention without departing from the true scope of the invention.