AU2005200113A1 - Logarithmic light intensifier for use with photoreceptor-based implanted retinal prosthetics and those prosthetics - Google Patents

Description

S&F Ref: 570848D1

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address of Applicant Actual Inventor(s): Address for Service: Invention Title: Second Sight, LLC, of P.O. Box 905, Santa Clarita, California, 91380-9005, United States of America Robert J. Greenberg, Abraham N. Seidman, Josehph H.

Schulman Spruson Ferguson St Martins Tower Level 31 Market Street Sydney NSW 2000 (CCN 3710000177) Logarithmic light intensifier for use with photoreceptorbased implanted retinal prosthetics and those prosthetics The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845c LOGARITHMIC LIGHT INTENSIFIER FOR USE WITH PHOTORECEPTOR BASED IMPLANTED RETINAL PROSTHETICS AND THOSE PROSTHETICS Field of the Invention This invention relates generally to retinal prosthetics and more particularly to a method and apparatus for enhancing retinal prosthetic performance.

This invention relates to directly modulating a beam of photons of sufficient energy onto 1o retinal prosthetic implants of patients who have extreme vision impairment or blindness.

Background of the Invention A healthy eye has photosensitive retinal cells rods and cones) which react to specific wavelengths of light to trigger nerve impulses. Complex interconnections among the retinal nerves assemble these impulses which are carried through the optic nerve to the is visual centers of the brain, where they are interpreted. Certain forms of visual impairment are primarily attributable to a malfunction of the photosensitive retinal cells.

In such cases, sight may be enhanced by a retinal prosthesis implanted in a patient's eye.

Michelson Patent No.4, 628,933) and Chow Patent Nos. 5,016,633; 5,397,350; 5,556,423) teach a retinal implant, or implants, of essentially photoreceptors facing out of the eye toward the pupil, each with an electrode which can stimulate a bipolar, or similar, cell with an electrical impulse. This bipolar cell is acted upon by the electrical stimulus, to send appropriate nerve impulses essentially through the optic nerve to the brain.

However, the photoreceptors do not appear to be sensitive enough to the ordinary levels of light entering the eye in that not enough current is produced to sufficiently stimulate the retinal cells. Consequently, a light amplifier, or "helper" device would be desirable.

Furness, et al. teach a "virtual retinal display", U.S. Patent No. 5,659,327, where "The virtual retinal display...utilises photon generation and manipulation to create a panoramic, high resolution, colour virtual image that is projected directly onto the retina of the eye...there being no real or aerial image that is viewed via a mirror or optics." Richard, et al. teach, U.S. Patent No. 5,369,415, direct retinal scan display including the steps of [R:\LIBLL] 16424_v2.doc:nyr providing a directed beam of light, modulating the beam of light to impress video information onto the beam of light, deflecting the beam in two orthogonal directions, providing a planar imager including an input for receiving a beam of light into the eye of an operator which involves a redirection diffractive optical element for creating a virtual image from the beam of light on the retina of the eye, and directing the beam of light scanned in two orthogonal directions and modulated into the input of the planar imager and the output of the planar imager into the eye of an operator." Sighted individuals can use these devices above for their intended uses. However, they appear unsuitable for use by blind individuals with implanted retinal prosthetics of the photoreceptor-electrode kind. It would seem that they do not provide enough light power.

Moreover, light amplitude cannot be arbitrarily increased because according to Slinly and Wolbarscht, Safety with Lasers and other Optical Sources, the retinal threshold damage is 0.4 Joules per square centimetre.

It is the object of the present invention to substantially overcome or at least ameliorate one or more of the disadvantages of the prior art.

Summary of the Invention Accordingly, the present invention provides an implantable neurostimulator for stimulation of a retina comprising: a source of electrical stimulus; two or more electrodes electrically coupled to said source of electrical stimulus; and an oxide layer deposited between at least one of said two or more electrodes, and the eye, wherein said at least one of said two or more electrodes, said oxide layer, and the eye form a capacitor.

In a preferred embodiment, the oxide layer prevents the flow of a direct electrical current from the neurostimulator to the eye.

Brief Description of the Drawings A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: [R:\LIBLL] 16424_v2.doc:nyr Figure 1 shows the logarithmic light amplifier with shutter, showing the incoming scene or view photons on the right and the eye on the left; Figure 2a shows a laser being modulated by a video signal and scanning the full extent of the implanted retinal prosthesis; Figure 2b shows a photoreceptor, associated electronics, and an associated electrode; Figure 2c shows the apparatus of Figure 2b but in a more rounded, smoother packaged form, likely more amenable for implantation into the eye; Figure 3a depicts tuned lasers external to the eye and tuned photo-detectors on an implanted retinal prosthesis; io Figure 3b depicts tuned lasers external to the eye and an array of tuned photo-detector pairs, one associated with each electrode, on an implanted retinal prosthesis; Figure 4 shows a sample of a typical biphasic wave form used to send data in the present invention; Figure 5 shows two different wavelengths, one to send in power, the other to send in information, to a single unit with two differently sensitive photoreceptors, one electronics package and one electrode; Figure 6 summarises three embodiments as shown previously; Figure 7 shows the external logarithmic amplifier (as "glasses"), a portable computer with mouse and joystick as setup aids; Figure 8 shows an implant unit (old in the art) with a photoreceptor and an electrode; Figure 9a shows a light-electronic feedback loop for knowing location on implant being scanned; Figure 9b shows one of different possible fiduciary markings including here points and lines for aiding knowing location on implant being scanned.

Description of the Preferred Embodiments The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is merely made for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the claims.

[R:\LIBLL] 16424_v2.doc:nyr This invention provides amplified light for artificial photoreceptors implanted in the eye of a patient who has lost the use of his/her normal photoreceptor retinal cells. The purpose of this amplified light is to effectively stimulate the artificial photoreceptors. The artificial photoreceptors, in turn, provide electrical stimulation through associated electrodes, usually via some electronics, to retinal cells, which are normally stimulated by living retinal photoreceptors such as cones and rods. The retinal cells, which get electrically stimulated by way of the artificial photoreceptors, are typically bipolar cells.

This stimulation to these non-photoreceptor retinal cells allows the patient to have at least some perception of what a normal eye would see. In order not to damage the retinal cells, io light is fed to the photoreceptor-electrode stimulators in the following ways.

Four preferred embodiments are described. In the first embodiment a single wavelength is relied upon to activate a combined photodetector-electronics-electrode implanted unit which then produces a negative pulse, followed by a time delay, followed by a negative pulse. In the first embodiment, a photoreceptor implanted in the eye acts to produce an electrical stimulation with an equal amount of positive and negative charge. A single light wavelength is received by the photoreceptor. The photoreceptor activates an electrode with associated electronics. The electronics produces a negative pulse followed by a time delay followed by a positive pulse. A net charge of zero is introduced into the eye by the electrode-originating electrical pulses. The preferred delay time is in the range 0.1 millisecond to 10 milliseconds, with the delay time of 2 milliseconds is most preferred. When the retinal cell is not being electrically stimulated, it returns to a rest and recovery state. It is then in a state, electrically, it was in prior to stimulation by the first electrical stimulation.

Starting with the logarithmic amplifier, an image receiver with a first converter for the image, converts the image into electrical signals. The signals are amplified, basically logarithmically, so as to provide brightness compression for the patient. The amplified electrical signal is converted by a second converter into a photon-based display wherein said photons of said display enter an eye through a pupil of said eye.

Photons (102) from a viewed scene (not shown) enter the logarithmic amplifier (1000) by way of the lens (101). The light amplifier (1000) has an image receiver a [R:\LIBLL] 16424_v2.doc:nyr first converter (103) of the image into electrical signals. an amplifier of said electrical signals whereby the overall amplification of said electrical signal according to a definite functional relationship between input signal to the amplifier and an output signal fiom the amplifier, a second converter (107) of said amplified electrical signal into a photon-based display such that the of display photons (108) enter an eye through the pupil (105) of the eye In the case where the imager is a type of video camera, the image receiver and conversion to electrical signals may occur in a package (old in the art).

A display that is a source of photons such as a laser (coherent light source) or a non-coherent source such as colored LEDs or a plasma display is used to send photons directly to an implant near the retina. These displays are made very bright, but not such as to impact negatively on the eye. In our cases, the patient has sufficient retinal degeneration so as to be unable to see without the aid of a retinal prosthetic. In the case where the display (photon source) is a laser that laserfi's scanned over the implanted photodetector-electronics-electrode array (Figure 2, in accordance with the scene being displayed to the eve. A scanning laser is a laser with scanning means (old in the art).

Referencing Figure 2a, the video signal is applied to a scanning laser a scanning laser being a laser with scanning means (old in the art). The scanning laser is scanned over the retinal prosthesis in a square orrectangular pattern or in a raster pattern with an exact fit to the prosthesis The video signal supplies amplitude from the data processor (Figure 1, and if desired (see Figure color information, of the scene being viewed, from the individual color amplifiers to the laser which information is used to modulate the laser.

In a preferred mode, the light amplifier (1000) is a logarithmic amplifier. In another preferred mode, the amplifier amplifies according to a different function than the logarithmic function or a modified logarithmic function, for example, an algebraic function such as a polynomial function multiplied by the logarithmic function The imager or camera lens is shown schematically as (101). The signal is logarithmically amplified as a whole at the electronic processor or the individual RGB (red. green, blue) or RGBY (red, green, blue. yellow) color components are individually logarithmically amplified Another color component mix of white light may be used. The individual amplification of separate color components allows for the relative super-amplification of one color to which the photoreceptors are particularly sensitive. If only a "black-and-white" contrast image is displayed. the "white" part of that image is logarithmically translated to the color, wavelength, to which the photoreceptors are most sensitive. This feature includes shifting the wavelength toward or to the near infrared or toward or to the near ultraviolet, according to what is needed to optimize the response of the implanted photosensitive elements.

Consequently, a mapping of the incoming image data to an appropriate output is possible. This mapping could be complex. for example, producing biphasic waveforms as shown in Figure 4 by appropriate timing of two lasers operating at different wavelengths and photosensitive elements uniquely sensitive to these wavelengths.

In a preferred mode, individual RGB (red, green, blue) or RGBY (red, green, blue, yellow) color components are amplified separately or amplified together (2) and separated out after the amplification. These color components may be used to stimulate particular photosensitive elements of the retinal implant(s). For example, a cell ("blue-sensation") producing a sensation of blue color is stimulated when the scene being transmitted to the eye has blue, which in the projected (into the eye) scene would have blue in the vicinity of that blue-sensation cell.

The logarithmic amplification is necessary to compress the range of original brightness. The normal eye does this automatically of closing down the pupil size, squinting and employing other electrochemical cellular mechanisms. This light amplifier accomplishes this necessary task by electronic logarithmic light amplification.

The light amplifier also includes an adjustable transformer or magnification of image size. A shutter or electronically turning the scanning laser on and off are not a necessary part of this embodiment.

In the second preferred embodiment of the light amplifier two or more wavelengths are used to communicate light energy to the eye to allow balanced biphasic stimulation with no net charge injection into the eye. A first wavelength is used to stimulate a first set of photoreceptors. These photoreceptors are connected so that the stimulation of the attached, or associated, electrodes results in a negative pulse.

This negative pulse provides retinal cell stimulation. Then the shutter cuts in and stops light transmission to the eye. The time of this light interruption is preferred in the range 0. I1 millisecond to 10 milliseconds, with the time of 2 milliseconds most preferred. The retinal cell is in a rest and recovery state so that it returns, electrically, to the state it was in prior to stimulation by the first particular wavelength of light. A second wavelength of light then stimulates a second set ofphotoreceptors which are sensitive to that wavelength of light; while the first set of photoreceptors are not affected. This second set of photoreceptors is connected so that the stimulation of the attached, or associated, electrodes results in a positive pulse. The net charge introduced into the retinal cells must balance, or equal, the net charge introduced by the negative pulse. Again, the shutter cuts in and stops light transmission. Again, the retinal cells rest and recover and the process repeats.

In the second preferred embodiment, Figure 3A. two scanning lasers, and are supplied with video signals, witheach laser operating at a different wavelength.

Advantageously, two or more photoreceptors (14) are on the implant. The two to types of photoreceptors are tuned to different frequencies of light, each of the frequencies being that of one of the emitting frequencies of the external lasers Figure 3B shows two incoming frequencies of light, (301) and (302). The light sources for the dual light frequencies (301), (302) is a unit (304) which is downstream in the information flow from the imager (Figure 1, (101), (103)) and amplifiers (Figure 1, The final output from the amplification stages is connected electrically or electromagnetically to the dual light frequency sources (304), in particular, dual scanning lasers operating with different wavelengths of light output.

Pairs (303) of different frequency wavelength) photoreceptors are placed on the eye-implant, each pair associated with an electrode (not shown).

Together, the two types of photoreceptors photodiodes) give rise to a biphasic current (Figure 4) at each electrode (not shown). Initially the rest state appears Next, one of the photoreceptors (13) has been activated by its corresponding laser The current amplitude is negative. After a time (42), laser and photoreceptor (13) shut down and the amplitude returns to zero. Next, the other laser (10) actives its corresponding (in light wavelength) photoreceptor (14) and the amplitude is positive by an amount (43) and for a duration Nominally, in absolute value, (41) and (42) However, in the case this is not exact, then the parameters (44) and (43) can be altered such that (41) (42) (43) where indicates multiplication. This can be accomplished by measuring (41) and (42) and then altering (43) or (44) or both to maintain charge balance.

A shutter is part of the second embodiment. The shutter (Figure 1. is of a mechanical design (old in the art), or an electronic shutter (old in the art) or an electro-optical shutter (old in the art). The shutter cuts off light from the logarithmic light amplifier (1000) to the pupil (105) of the eye This decreases the total time that light strikes the photoreceptors (Figure 3a. (Figure 3b, 303) Consequently, the time during w'hich the bipolar, or similar cells, are stimulated is decreased. Because the eye is not functioning as originally intended, tile bipolar, or similar, cells are thoughlt to need this "down-time" to continue to function properly.

S An aspect of this invention is the use of two or more wavelengths to allow balanced biphasic stimulation with no net charge injection into the eye. As long as a biphasic type of electrical stimulation. Nwhere equal amounts of positive charge and negative charge in the form of ionic carriers or electrons or other charge carriers, enter the vitreous fluid of the eye, the electrical effect on the eye is not harmful. If direct current is supplied to the eye, intemrnally, a charge imbalance results. This excess of charge has been found to be harmful to cells. Consequently, direct current can harm the bipolar and other cells. Advantageously, the biphasic electrical stimulation tends to avoid this harm to the cells because no excess charge accumulates.

A third embodiment that is a cross, so to speak, between the first and second embodiments uses two different wavelengths and two different types of diodes, each responsive to a corresponding wavelength. In this embodiment, one wavelength is used to pump in a high constant level of light to supply power to the electronics component.

The other wavelength is used to send in information via amplitude, frequency, phase, pulse-width modulation, or combinations thereof. The stimulation pulse from the electronics to the electrode to the retinal cell is generated in a fashion similar to the pulses generated in the first embodiment, with a single wavelength.

The third embodiment uses two different wavelengths and two different types of diodes, each responsive to a corresponding wavelength. (See Figure 3b, (301), (302)) In this embodiment, one wavelength (Figure 5, (501)) is used to pump in a high constant level of light to supply power to the electronics component (502). The other wavelength (503) is used to send in information via amplitude, frequency, phase, pulsewidth modulation. or combinations thereof to the electronics component (502). The stimulation pulse from the electronics (502) to the electrode (504) to the retinal cell is generated in a fashion similar to the pulses generated in the First embodiment, with a single wavelength.

See Figure 6. Figure 6 summarizes in block form the preceding three embodiments. In the first embodiment thcre is one wavelength (601) input to a single diode (602) with electronics (603) and electrode (604). Either digitally or by analogue means, old in the art. a d. c. signal occurring after the absorption of photons by the photoreceptor is converted by the electronics to a signal (600) of the type shown in Figure 4. at the electrode. In the second embodiment. for two different wavelengths (610), (611), both carrying power and information, impinging on two different photoreceptors (612). (613). the electronics (6033), digital or analogue, again produce the waveform (600) of Figure 4 at the electrode (604). In the third embodiment. for two different photoreceptors (620), (621). the first receiving a steady state power wavelength (622), the second receiving a signal wavelength (623), the electronics (6034), digital or analogue, produces the signal (600) of Figure 4 at the electrode (604).

The electronic circuitry of (603), (6033) and (6034) may be different.

A fourth embodiment is that of the logarithmic light amplifier (1000) itself, without any special implantable photoreceptors. This last embodiment may require a low duty cycle when used with photoreceptors (Figure 8, connected to an electrode (82) without any electronics. It relies upon the intrinsic capacitance of an oxidizable electrode, which acquires capacitance with the buildup of an insulating oxidized layer toward the ionizable fluid present in the eye as vitreous fluid, or fluid directly associated with the eye.

In a first set of embodiments, the addition of a shutter (Figure 1, with an off time of from 0.5 ms to 10 ms, most preferably 2 ms provides a mechanism to provide that off time (Figure 4, However, in a second set of embodiments, the time each laser is on can be controlled by electronic means (old in the art) within the laser to provide equal positive pulses and negative pulses, equal with respect to total signed charge introduced into a retinal cell. The first and second sets of embodiments may be completely or partially coincident.

Another aspect of all of the embodiments is incorporation of both optical and electronic magnification of the image, as for example, the incorporation of an optical zoom lens, as well as electronic magnification. Optical magnification of the image (see Figure 1) is accomplished by use of a zoom lens for the camera lens (101). Electronic magnification is accomplished electronically in an electronic data processing unit or Consequently. it is feasible to focus in on items of particular interest or necessity.

With proper adjustment, proper threshold amplitudes of apparent brightness obtain, as well as comfortable maximum thresholds of apparent brightness. Therefore, to adjust for these, a sixth aspect is incorporated in all of the embodiments such that proper adjustment for the threshold amplitudes and maximum comfortable thresholds can be made.

To makes color vision available, to a degree: another aspect is incorporated. To the extent that individual stimulation sites bipolar cells) give different color perceptions upon stimulation, the color of selected pixels of the viewed scene is correlated with a specific pair of photoreceptors located so as to electrically stimulate a specific type of bipolar cell to provide the perception of color vision In order to help implement these last two aspects of the preferred embodiments of this invention, apparent brightness control and the presentment of apparent color, the logarithmic amplifier also incorporates within itself, a data processing unit which cycles electrical pulses of varying amplitude and/or frequency and/or phase and/or pulse width through the various photodetector-electrodes and spatial combinations thereof, and, interrogates the patient, who then supplies the answers, setting up proper apparent brightness and apparent color. A different aspect of the embodiments utilizes a plug in accessory data processor (Figure 7, with display (72) and data input device or devices such as a keyboard mouse or joystick Figure 7 show the plug in unit (71) which plugs (76) into the logarithmic light amplifier (1000) to provide additional data processing ability as well as expanded data input and data display capability.

In order for the scanning laser to correctly scan the retinal implant prosthetic photoreceptors, it ishelpful if some feedback is provided to it. One aspect of the different embodiments is the presence of a feedback loop using some of the reflected light from the scanning laser itself. One aspect of the feedback loop is to use regions of different reflectivity on the surface of the retinal implant which allow the location, or relative location, of the scanning laser light beam to be determined.

A scanning laser feedback is provided in the different embodiments of the invention. An imaging (Figure 9a) of the retinal implant from the reflected (92) incoming scanning laser beam see Figure 9a, (Figure land Figure 2a, (Figure 3a, reflected back from the retinal implant (Figure 9, can be used to provide real-time feedback information, utilizing a second imager (93) viewing into the eye and a data processor unit (94) tied into the scanning laser's scan control unit Another aspect of the embodiments (Figure 9b) utilizes multiple fiduciary reflective or light absorptive points (96) and/or lines (97) on theretinal implant such that the frequency and signal pattern, more generally. (100) of the high 11 reflectivity from these reflective. or absorptive lines/point for a given rate of scanning by the scanning laser can be used to correct the scanning direction from the different frequency patterns. some indicating correct scanning, others indicating an incorrect scanning.

While the invention herein disclosed has been described by means of specific embodiments and applications thereof. numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.

Claims (3)

1. An implantable neurostimulator for stimulation of a retina comprising: a source of electrical stimulus; two or more electrodes electrically coupled to said source of electrical stimulus; and an oxide layer deposited between at least one of said two or more electrodes, and the eye, wherein said at least one of said two or more electrodes, said oxide layer, and the eye form a capacitor.

2. The implantable neurostimulator according to claim 1, wherein said oxide layer prevents the flow a direct electrical current from said neurostimulator to the eye.

3. An implantable neurostimulator for stimulation of a retina, said neurostimulator being substantially as hereinbefore described with reference to any one embodiment, as that embodiment is depicted in the accompanying drawings. Dated 12 January, 2005 Second Sight, LLC Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON