The present invention relates to a method and apparatus for facilitating artificial vision and, particularly, but not exclusively, to a method and apparatus for facilitating artificial vision using retinal electrical neuro-stimulation.
The natural functioning of a healthy human eye involves receiving light through the eye-lens, generating neural messages at the retina and sending the neural messages to the brain. Light entering the retina triggers a photochemical reaction in the photoreceptors of the retinal tissue (i.e. cones and rods). Neural responses are transmitted in the retinal neurons, via the optic nerve to the brain. The brain processes these signals to produce meaningful visual percepts (vision).
There are many conditions which can result in the failure of human vision. Attempts have been made to stimulate retinal ganglion cells with signals processed from image sensors, in order to reproduce vision.
There are two main types of retinal ganglion cells (RGCs), On-type and Off-type and they respond differently to light stimulation. The response is complex, but generally speaking, the onset of light stimulation produces a transient burst firing of the On-type cells which will remain sustained during photic stimulus. Off-type cells will remain inactive until the photic stimulus stops. These cells then respond with a sustained burst of action potentials.
It is known that high frequency electrical stimulation (HFS) of the retinal tissue can trigger differential responses in both ON brisk transient and OFF brisk transient RGCs. Although the response of the RGCs following light stimulation is understood, to date their electrical stimulation has not been able to reproduce neural encoding of visual stimuli that result in wholly meaningful visual percepts.
In accordance with a first aspect, the present invention provides a method of facilitating artificial vision, comprising the steps of stimulating retinal on-type and off-type cells, and affecting resulting neural responses of the cells to reproduce more natural on-type and off-type cell behaviour.
In an embodiment, the step of stimulating comprises the step of applying a primary stimulating signal to stimulate the retinal On-type and Off-type neurons. The step of affecting comprises providing a secondary stimulating signal to affect the neural responses.
In an embodiment, the primary stimulating signal and secondary stimulating signals are applied at different stimulating sites in the visual system.
In an embodiment, the primary stimulating signal is applied at the retina. In an embodiment, the secondary stimulating signal is applied in the vicinity of the optic nerve where the neural axons gather together. The secondary stimulating signal may be applied proximate or at the optic disc, or at the optic nerve.
In an embodiment, the primary stimulating signal is applied at a proximal portion of a retinal ganglion cell. It may be applied at the soma or initial segment of the axon. In an embodiment, the step of affecting comprises providing a secondary stimulating signal to the retinal ganglion cells distal of the primary stimulating location.
In an embodiment, the secondary stimulating signal modulates the neural responses elicited in the neural axons by the primary stimulating signals.
Advantageously, in an embodiment, the primary stimulus and secondary stimulus enables mimicking of the behaviour of a healthy retina by establishing On and Off responses in isolation. Advantageously, by applying this form of stimulation, the applicants believe that a more physiologically realistic encoding of visual stimuli can be achieved.
In an embodiment, the stimulation applied by the primary and secondary signals is electrical stimulation applied by electrodes positioned at primary and secondary stimulation sites.
In an embodiment, the number of and distribution of electrodes at the primary stimulation site and secondary stimulation site may be varied to influence spatial application of the primary and secondary signals.
In embodiments the primary group of electrodes may be arranged in a rectilinear array, a hexagonal mosaic or octagonal mosaic. They may be distributed randomly or arranged in concentric circles or in any other pattern.
In an embodiment, the secondary group of electrodes may be arranged in an arcuate form near the optic disc or any arrangement or pattern or as cuff about the optic nerve.
In an embodiment, the electrode return configuration may be selected to influence the spatial application of the signals.
In an embodiment, the primary stimulating signal and secondary stimulating signal are delivered sequentially.
In an embodiment, the time periods of the primary and the secondary stimulating signals may be varied to vary stimulation. Further, a time period between application of the primary stimulation signal and secondary stimulation signal may be varied.
In an embodiment, the method comprises the further step of monitoring the signals produced by the stimulation to determine the effect of the stimulation. In an embodiment, the voltage waveforms and the neural responses of the tissue are monitored.
In an embodiment, the method comprises the further step of monitoring local field potentials evoked by the application of the signals, and using this to adjust stimulation.
In accordance with a second aspect, the present invention provides an apparatus for facilitating artificial vision, comprising a stimulator arrangement arranged to stimulate retinal on-type and off-type cells to elicit neural responses, and an affecting arrangement arranged to affect the neural responses to reproduce more natural on-type and off-type cell behaviour.
In accordance with a third aspect, the present invention provides a method of facilitating artificial vision, comprising the steps of stimulating retinal ganglion cells, and affecting resulting neural responses of the cells.
In an embodiment, the step of stimulating comprises the step of applying a primary stimulating signal to a proximal portion of a retinal neural ganglion and applying a secondary stimulating signal to effect the neural responses produced by the primary stimulating signal.
This aspect of the invention may have any or all of the features of the aspects of the invention discussed above. In accordance with a fourth aspect, the present invention provides an apparatus for facilitating artificial vision, comprising a stimulator arrangement arranged to simulate retinal ganglial cells to elicit neural responses, and an affecting arrangement arranged to affect the neural responses.
In an embodiment, the stimulator arrangement is arranged to apply a primary stimulating signal to a proximal portion of a retinal ganglial cell, and a secondary stimulation signal to a distal portion of a retinal ganglial cell, to affect the neural response produced by the primary signal.
In accordance with a fifth aspect, the present invention provides a computer program, comprising instructions for controlling a processor to implement a method in accordance with the first or fifth aspects of the invention.
In accordance with a sixth aspect, the present invention provides a computer readable medium, providing a computer program in accordance with the fifth aspect of the invention.
In accordance with a seventh aspect, the present invention provides a data signal, comprising a computer program in accordance with the first aspect of the invention.
Features and advantages of the present invention will become apparent from the following description of embodiments thereof, by way of example only, with reference to the accompanying drawings in which:
An apparatus in accordance with an embodiment of the present invention is broadly illustrated in
In more detail, the image sensor 102 in this embodiment (a digital camera) captures visual information in the form of various frames. The image sensor 102 can be a camera or any other device which is capable of capturing visual information in the form of images. The processing unit 104 receives the visual information through image sensor 102. The processor 106 acquires, digitises and processes a series of frames and stores these in the memory unit 108. After processing, a series of stimulating waveforms are delivered through the plurality of stimulating sources 112 (current sources in this embodiment) to two groups of stimulating electrodes 114, 116. The parameters of the stimulating waveforms are correlated to the visual information captured by the image sensor 102. The primary group of electrodes 114 is placed in close proximity to the retinal neural cells and these will be used to deliver a series of primary stimulation waveforms which will recruit target retinal cells. These primary stimulation waveforms will electrically stimulate the RGCs to generate neural responses. The secondary group of electrodes 116 is distributed in the vicinity of the optic disc, where the axons of the RGC converge to form the optic nerve. These electrodes 116 operate as an arrangement which affects the primary neural responses by delivering a series of secondary stimulation waveforms. This modulates the neural responses generated by the primary stimulation of the retina. The modulated neural responses are arranged to more closely replicate the natural neural encoding of light stimuli of On-RGCs and Off-RGCs. The modulated neural responses are carried through the optic nerve to the brain of the patient. In the patient's brain, these responses produce a meaningful visual perception of the real world captured through the image sensor 102.
The apparatus 100 also comprises a telemetry unit 110. The telemetry unit is arranged to measure impedance and local field potentials at the stimulating sites, following electrical stimulation of the On-type and Off-type cells. This information can be used to “tune” the stimulation (see later).
In an embodiment, an implant comprising the primary group 114 and the secondary group 116 of stimulating electrodes is installed in patient's eye. The implant is a device capable of communicating with external electronics for example with the stimulation sources 112 and the telemetry unit 110. The implant can be powered by the processor 106 through a wireless link e.g. radiofrequency induction. The processor 106 sends information to the implant to deliver the primary and secondary simulation signals at target sites in accordance with the visual information received from the image sensor 102.
A number of different electrode arrangements and patterns may be used at the primary stimulating sites and secondary stimulating sites. Different electrode configurations (type of electrode) may also be utilised.
Referring now to
In this diagram, 201 represents the optic disc, 203 and 205 represent inactive and active electrodes in the primary group of stimulating elements respectively. A primary electrode is “active” if it is being stimulated by the primary stimulation signal. This will depend on the signals generated by the image sensor 102 and the waveforms generated by the processing unit 104 to operate the stimulation sources 112. The active electrodes effectively represent the effect of the image being sensed by a sensor 102. The primary stimulating electrodes 203, 205 are arranged in a rectilinear array in this embodiment, following a hexagonal mosaic. The secondary stimulating electrodes 207 are arranged as two concentric ring sections.
In this embodiment, the type of electrodes used as the primary stimulating electrodes are of a concentric configuration. This configuration may be used to achieve focus to electrical fields for the primary electrodes.
The configuration for the electrode may be selected, as well as the electrode distribution patterns.
The electrodes may be distributed in any pattern, hexagonally, octagonal pattern, concentric circles or any other pattern. They may be randomly distributed.
As mentioned previously, both groups (primary and secondary) of electrodes can be connected to a telemetry unit (see
Referring now to
Different electrode return configurations may be used in order to provide spatial selectivity in different embodiments. In a monopolar configuration, the return electrode, generally of larger size than the stimulating electrodes, is placed far from the active electrodes. This will produce a wide spread of the electric current and therefore recruitment of a larger retinal tissue area. The bipolar configuration utilises one of the neighbouring electrodes within the electrode array as a return. This will, to some extent, reduce the spread of the electric field and therefore produce a more contained electrical stimulation, while activating the neural tissue at both sides, the active electrode and the return electrode. In an electrode array where the spatial distribution is in lattice form e.g. hexagonal, then the surrounding electrode configuration acts as a return electrode. That is, with a hexagonal configuration, the hexagonal guard acts a return electrode. Equivalent arrangements may be used for octagonal or square lattices or any other shape lattice. This provides focussed stimulation while increasing activation thresholds. Note that the quasi-monopolar configuration combines a monopolar and a hexapolar approach. This will provide contained stimulation with lower thresholds. Concentric configurations can also be used to replace the hexapolar configurations, to achieve focused electrical fields. These return configurations can be used, in embodiments, in combination with multiplexing techniques to enhance performance.
In the above embodiments, primary stimulating signals are delivered at the retina and the secondary stimulating signals at the optic disc or optic nerve. The invention is not limited to this. The stimulating signals may be delivered anywhere in the visual system.
It will be appreciated that embodiments of the present invention may utilise computer programs to facilitate control of the apparatus. These programs may be in the form of software running an appropriate hardware. They may be in the form of programmable gate arrays (or field programmable gate arrays) or in any other form. Software may be stored in memory, or on other computer readable media, or delivered as signals.
In embodiments, the processing unit that processes images and generates stimulation parameters (for example, the processing unit 104 of
In the above described embodiment, the processing unit is external to the human body. In other embodiments, the processing unit may be provided internally. In embodiments, parts of the apparatus may be internal (stimulating electrodes, for example) and parts external. The parts internal and external may be varied, depending on the embodiment. For example, in some embodiments the telemetry unit and stimulation sources circuitry may be internal, in other embodiments they may be external.
It will be appreciated that the apparatus is not limited to the structure disclosed above with reference to
In the above embodiment, the retinal ganglion cells are stimulated by electrodes placed proximate the cells. In embodiments, electrodes may stimulate other cells that in turn stimulate retinal ganglion cells. For example, they may stimulate bi-polar cells and/or retina amacrine cells. Primary stimulation may be applied here and then secondary stimulation distal on the RGC.
The above embodiments show and describe various electrode arrays. It will be appreciated that other electrode arrays than shown may be used in other embodiments, and other electrode arrangements.
Embodiments of the present invention have applicability to visual prosthesis. Applicants believe that providing appropriate neural encoding in retinal prosthesis is key to elicit more meaningful visual percepts.
It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.
Number | Date | Country | Kind |
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2016902473 | Jun 2016 | AU | national |
Filing Document | Filing Date | Country | Kind |
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PCT/AU2017/050645 | 6/23/2017 | WO | 00 |