Abstract:
The invention is a retinal prosthesis with an improved configuration mounting necessary components within and surrounding the eye. The present invention better allows for the implantation of electronics within the delicate eye structure. The invention further limits the necessary width of a thin film conductor passing through the sclera by use of a multiplexer external to the sclera and a demultiplexer internal to the sclera.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional application of U.S. patent application Ser. No. 11/880,009, filed Jul. 19, 2007, which is a divisional application of U.S. patent application Ser. No. 10/918,112 filed Aug. 13, 2004, which claims priority of provisional Patent Application No. 60/574,130 filed May 25, 2004, the disclosure of which are both incorporated herein by reference. 
     
    
     GOVERNMENT RIGHTS NOTICE 
       [0002]    This invention was made with government support under grant No. R24EY12893-01, awarded by the National Institutes of Health. The government has certain rights in the invention. 
     
    
     FIELD OF THE INVENTION 
       [0003]    The present invention is generally directed to a visual prosthesis and more specifically to an improved mechanical and electrical configurations for retinal prosthesis for artificial vision. 
       BACKGROUND OF THE INVENTION 
       [0004]    In 1755 LeRoy passed the discharge of a Leyden jar through the orbit of a man who was blind from cataract and the patient saw “flames passing rapidly downwards.” Ever since, there has been a fascination with electrically elicited visual perception. The general concept of electrical stimulation of retinal cells to produce these flashes of light or phosphenes has been known for quite some time. Based on these general principles, some early attempts at devising a prosthesis for aiding the visually impaired have included attaching electrodes to the head or eyelids of patients. While some of these early attempts met with some limited success, these early prosthetic devices were large, bulky and could not produce adequate simulated vision to truly aid the visually impaired. 
         [0005]    In the early 1930&#39;s, Foerster investigated the effect of electrically stimulating the exposed occipital pole of one cerebral hemisphere. He found that, when a point at the extreme occipital pole was stimulated, the patient perceived a small spot of light directly in front and motionless (a phosphene). Subsequently, Brindley and Lewin (1968) thoroughly studied electrical stimulation of the human occipital (visual) cortex. By varying the stimulation parameters, these investigators described in detail the location of the phosphenes produced relative to the specific region of the occipital cortex stimulated. These experiments demonstrated: (1) the consistent shape and position of phosphenes; (2) that increased stimulation pulse duration made phosphenes brighter; and (3) that there was no detectable interaction between neighboring electrodes which were as close as 2.4 mm apart. 
         [0006]    As intraocular surgical techniques have advanced, it has become possible to apply stimulation on small groups and even on individual retinal cells to generate focused phosphenes through devices implanted within the eye itself. This has sparked renewed interest in developing methods and apparati to aid the visually impaired. Specifically, great effort has been expended in the area of intraocular retinal prosthesis devices in an effort to restore vision in cases where blindness is caused by photoreceptor degenerative retinal diseases such as retinitis pigmentosa and age related macular degeneration which affect millions of people worldwide. 
         [0007]    Neural tissue can be artificially stimulated and activated by prosthetic devices that pass pulses of electrical current through electrodes on such a device. The passage of current causes changes in electrical potentials across visual neuronal membranes, which can initiate visual neuron action potentials, which are the means of information transfer in the nervous system. 
         [0008]    Based on this mechanism, it is possible to input information into the nervous system by coding the information as a sequence of electrical pulses which are relayed to the nervous system via the prosthetic device. In this way, it is possible to provide artificial sensations including vision. 
         [0009]    One typical application of neural tissue stimulation is in the rehabilitation of the blind. Some forms of blindness involve selective loss of the light sensitive transducers of the retina. Other retinal neurons remain viable, however, and may be activated in the manner described above by placement of a prosthetic electrode device on the inner (toward the vitreous) retinal surface (epiretinal). This placement must be mechanically stable, minimize the distance between the device electrodes and the visual neurons, and avoid undue compression of the visual neurons. 
         [0010]    In 1986, Bullara (U.S. Pat. No. 4,573,481) patented an electrode assembly for surgical implantation on a nerve. The matrix was silicone with embedded iridium electrodes. The assembly fit around a nerve to stimulate it. 
         [0011]    Dawson and Radtke stimulated cat&#39;s retina by direct electrical stimulation of the retinal ganglion cell layer. These experimenters placed nine and then fourteen electrodes upon the inner retinal layer (i.e., primarily the ganglion cell layer) of two cats. Their experiments suggested that electrical stimulation of the retina with 30 to 100 uA current resulted in visual cortical responses. These experiments were carried out with needle-shaped electrodes that penetrated the surface of the retina (see also U.S. Pat. No. 4,628,933 to Michelson). 
         [0012]    The Michelson &#39;933 apparatus includes an array of photosensitive devices on its surface that are connected to a plurality of electrodes positioned on the opposite surface of the device to stimulate the retina. These electrodes are disposed to form an array similar to a “bed of nails” having conductors which impinge directly on the retina to stimulate the retinal cells. U.S. Pat. No. 4,837,049 to Byers describes spike electrodes for neural stimulation. Each spike electrode pierces neural tissue for better electrical contact. U.S. Pat. No. 5,215,088 to Norman describes an array of spike electrodes for cortical stimulation. Each spike pierces cortical tissue for better electrical contact. 
         [0013]    The art of implanting an intraocular prosthetic device to electrically stimulate the retina was advanced with the introduction of retinal tacks in retinal surgery. De Juan, et al. at Duke University Eye Center inserted retinal tacks into retinas in an effort to reattach retinas that had detached from the underlying choroid, which is the source of blood supply for the outer retina and thus the photoreceptors. See, e.g., E. de Juan, et al., 99 Am. J. Ophthalmol. 272 (1985). These retinal tacks have proved to be biocompatible and remain embedded in the retina, and choroid/sclera, effectively pinning the retina against the choroid and the posterior aspects of the globe. Humayun, U.S. Pat. No. 5,935,155 describes the use of retinal tacks to attach a retinal array to the retina. Alternatively, an electrode array may be attached by magnets or glue. U.S. Pat. No. 5,109,844 to de Juan describes a flat electrode array placed against the retina for visual stimulation. 
         [0014]    Any device for stimulating percepts in the retina must receive a signal describing a visual image along with power to operate the device. The device can not be powered by wires as any connection through the skin will create the risk of infection. Battery power is not practical as batteries are bulky and surgery is required to replace them. Such signal and power may be transmitted into the eye inductively as shown in Humayun U.S. Pat. No. 5,935,155. Humayun uses a primary (external) coil in front of the eye, possibly encased within the rim of a pair of glasses, and a secondary (internal) coil within the lens capsule or around the sclera just under the conjunctiva. Implanting within the lens capsule is difficult surgery and only allows for a small diameter coil. Larger coils are more efficient, can receive more power with less resulting temperature rise per unit of power received. Implanting around the sclera under the conjunctiva and near the surgical limbus (that is at the front of the eye) allows for a larger coil but may cause irritation or damage to the conjunctiva if the coil is placed in front near the cornea. 
         [0015]    U.S. patent application Ser. No. 09/761,270, Ok, discloses several coil configurations including a configuration where the coil is offset about 45 degrees from the front of the eye. The offset configuration allows the primary and secondary coils to be placed closer together allowing for better inductive coupling. The bridge of nose partially blocks placement of a primary coil when placed directly in front of the eye. 
         [0016]    Vision simulations show that approximately 1000 pixels are needed to achieve basic visual functions such a face recognition and reading. It would be difficult or impossible to mount the electronics need for 1000 pixels within the eye. Even if the electronics could be fit within the eye, heat dissipation would be a major issue. It would be equally difficult to pass a cable capable of caring 1000 signal wires through the sclera. New mechanical and electrical configurations are needed to supply such a high density electrode array. 
       SUMMARY OF THE INVENTION 
       [0017]    The invention is a retinal prosthesis with an improved configuration mounting necessary components within and surrounding the eye. The present invention better allows for the implantation of electronics, capable of high resolution display, within the delicate eye structure. The invention further limits the necessary width of a thin film conductor passing through the sclera by use of a multiplexer external to the sclera and a demultiplexer internal to the sclera. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a perspective view of the implanted portion of the preferred retinal prosthesis. 
           [0019]      FIG. 2  depicts a retinal prosthesis with a secondary processing chip, including a demultiplexer, in the retina. 
           [0020]      FIG. 3  depicts a retinal prosthesis with a secondary processing chip, including a demultiplexer, within the sclera but not on the retina. 
           [0021]      FIG. 4  depicts a retinal prosthesis with a polymer thin film based secondary processor, including a demultiplexer, on the retina. 
           [0022]      FIG. 5  depicts a retinal prosthesis with a polymer thin film based secondary processor, including a demultiplexer, within the sclera, but not on the retina. 
           [0023]      FIG. 6  is an external profile view of a user wearing the external portion of the retinal prosthesis. 
           [0024]      FIG. 7  is a description of the preferred demultiplexer and electrode chip. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    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 made merely for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the claims. 
         [0026]      FIG. 1  shows a perspective view of the implanted portion of the preferred retinal prosthesis. An electrode array  10  is mounted by a retinal tack or similar means to the epiretinal surface. The electrode array  10  is electrically coupled by a cable  12  which pierces the sclera and is electrically coupled to an electronics package  14 , external to the sclera. It is advantageous to encase the electronics within a hermetic package. This can be accomplished by use of a metal, ceramic polymer or a combination of these materials case, or by applying a thin film hermetic coating such as described in US patent application 20020038134 Package for an Implantable Medical Device and 20020120296, Implantable Device Using Ultra-Nanocrystalline Diamond. An electronics package with a coil mounted on the lateral surface of the retina is described in US patent application attorney docket S293-USA. All of the above applications are incorporated herein by reference. 
         [0027]    It is advantageous to mount electronics external to the sclera, as the fatty tissue there is less heat sensitive, and blood flow rapidly dissipates excess heat. The vitreous within the eye is does not change often and the retina is very heat sensitive. 
         [0028]    The electronics package  14  is electrically coupled to a secondary inductive coil  16 . Preferably the secondary inductive coil  16  is made from wound wire. Alternatively, the secondary inductive coil may be made from a thin film polymer sandwich with wire traces deposited between layers of thin film polymer. The electronics package  14  and secondary inductive coil  16  are held together by a molded body  18 . The molded body  18  may also include suture tabs  20 . The molded body narrows to form a strap  22  which surrounds the sclera and holds the molded body  18 , secondary inductive coil  16 , and electronics package  14  in place. The molded body  18 , suture tabs  20  and strap  22  are preferably an integrated unit made of silicone elastomer. Silicone elastomer can be formed in a pre-curved shape to match the curvature of a typical sclera. However, silicone remains flexible enough to accommodate implantation and to adapt to variations in the curvature of an individual sclera. The secondary inductive coil  16  and molded body  18  are preferably oval shaped. A strap can better support an oval shaped coil. 
         [0029]    It should be noted that the entire implant is attached to and supported by the sclera. An eye moves constantly. The eye moves to scan a scene and also has a jitter motion to improve acuity. Even though such motion is useless in the blind, it often continues long after a person has lost their sight. It is an advantage of the present design, that the entire implanted portion of the prosthesis is attached to and supported by the sclera. By placing the device under the rectus muscles with the electronics package in an area of fatty issue between the rectus muscles, eye motion does not cause any flexing which might fatigue, and eventually damage, the device. 
         [0030]    As we improve the resolution of retinal prostheses, the number of electrodes increases. As the number of electrodes increases the number of wires between the electronics package and the electrode array must increase. This increase requires a wider thin film cable piercing the sclera. If the thin film cable is too wide, the sclerotomy may not heal properly.  FIG. 2-5  present embodiments to provide for a narrower thin film cable between the electronics, external to the sclera, and the electrode array within the sclera. 
         [0031]    A common method of reducing the conductor count in cables, is the use of a multiplexer and demultiplexer. However, multiplexers, like any electronic circuit, present unique problems when implanted within the human body. All electronics must be sealed to prevent the saline body fluids from harming the electronics and to prevent the electronics from harming the body. Each electrical wire entering and exiting the electronics package must also be sealed. Therefore it is advantageous the limit the number of such wire electronics package interconnects. While it is easy to include a multiplexer within the electronics package, it is more difficult to house a demultiplexer within the sclera. 
         [0032]      FIG. 2 , depicts the preferred embodiment where a computer chip  110 , including a demultiplexer is placed directly on the retina. The demultiplexer interconnects with the thin film cable  112  on one side and includes electrode openings, for contacting the retina on the other side. This is best accomplished by create feedthroughs in the silicon chip to allows electrodes on one side of the chip and connection to the flexible cable on the other side of the chip (described in more detail in  FIG. 7 . Cable  112  pierces the sclera and attaches to an electronics package  114 . The electronics package connects to a coil  116 . The chip  110  must be coated with a thin film hermetic coating as described above. This is the simplest most cost effective method of providing a demultiplexer within the sclera. 
         [0033]    Silicon chips such as chip  110  are necessarily flat. It is possible through polishing to slightly curve one side, but the curvature is limited as the electrical circuit on the chip must be flat. It is possible that chip  110  may be a series of silicon chips bonded to a flexible membrane to approximate the curvature of the retina. This allows for a larger electrode array than would be possible with a single chip  110 . 
         [0034]    However, the retina is extremely delicate and can be damaged by either the weight of such a demultiplexer chip or chips, or by the heat generated by the demultiplexer chip. If the chip can not be made light enough or cool enough to attach to the sclera, other solutions are needed. 
         [0035]      FIG. 3 , depicts an alternate embodiment where a demultiplexer chip  224  is positioned within the eye, but not on the retina. Electrode array  210  is connected to the demultiplexer  224  by a wide cable  226 , and demultiplexer  224  is connected to the electronics package  214  by a narrow cable  212 . Narrow cable  212  pierces the sclera to attach to an electronics package  214 . The electronics package  214  also connects to a coil  216 . This embodiment requires two interconnects on the external electronics package  214 , one for the coil, and a low density interconnect to a cable piercing the sclera. This cable piercing the sclera is connected to another low density interconnect on the demultiplexer chip within the sclera. Finally there must be a high density interconnect on the demultiplexer connected to a thin film electrode array. While this solution is more complex, it moves the weight and heat of the demultiplexer off the retina. 
         [0036]      FIG. 4 , depicts yet another embodiment where the demultiplexer is not a silicon based integrated circuit, but an integrated circuit deposited directly on the thin film electrode array  310 . The demultiplexer interconnects with the thin film cable  312  on one side and includes electrode openings, for contacting the retina on the other side. Cable  312  pierces the sclera and attaches to an electronics package  314 . The electronics package connects to a coil  316 . Several integrated circuit manufacturers are building integrated circuits on Mylar thin films. The same technique can be used to build integrated circuits on polyimide or other biocompatible thin film polymers. By depositing the demultiplexer circuitry directly on the thin film, one avoids the weight of a silicon based integrated circuit and the possible damage to the retina cause by the weight of a silicon based demultiplexer. Further, building the demultiplexer circuit directly on the thin films avoids the need for a hermetic interconnection to a demultiplexer chip or a hermetic coating on the chip. If the heat output of a thin film based demultiplexer is sufficiently small, the demultiplexer can be built directly into the electrode array, completely eliminating the need for a thin film wide enough to include one connector for each electrode. 
         [0037]    If the heat output of a thin film demultiplexer is likely to cause damage to the retina, another embodiment, shown in  FIG. 5 , provides a thin film demultiplexer between the electrode array and electronics package, but sufficiently distant from the retina, to avoid heat damage.  FIG. 5 , depicts an alternate embodiment where a thin film demultiplexer  424  is positioned within the eye, but not on the retina. Electrode array  410  is connected to the demultiplexer  424  by a wide cable  426 , and demultiplexer  424  is connected to the electronics package  414  by a narrow cable  412 . Narrow cable  412  pierces the sclera to attach to an electronics package  414 . The electronics package  414  connects to a coil  416 . It is possible to form the electrode  410 , wide cable,  426 , demultiplexer  424 , and thin cable  412  on a single thin film substrate. While this solution is more complex, it moves the heat of the demultiplexer off the retina. 
         [0038]      FIG. 6  depicts the profile of a user wearing the external portion of the retinal prosthesis. The entire device may be built into the temple of a pair of glasses. A camera  530  collects a video image and transmits data to an external electronics package  532 . A battery  534  powers the camera  530 , external electronics package  532 , and provides power to a primary inductive coil  536 . The primary inductive coil  536  sends power and data through the skin and skull to the secondary inductive coil  16 . Maximum efficiency is obtained when the primary inductive coil  536  and secondary inductive coil  16  are the same size, shape and as close together as possible. 
         [0039]      FIG. 7 , depicts the preferred demultiplexer chip  110 . A silicon substrate  610  has a demultiplexer  612  applied by conventional means. Micromachining techniques are used to create voids in the silicon substrate  610 , which are filled with conductive feedthroughs  616 . Electrodes  614 , for contact with the retina, are applied to the conductive feedthroughs  616  by electroplating or other means. A thin film hermetic coating  618  is applied to the silicon substrate  610  allowing voids for electrodes  614  and contacts  620 . Finally a thin film cable  622  is attached to the contacts  620  to supply power and signal to the demultiplexer chip. 
         [0040]    Accordingly, what has been shown is an improved retinal prosthesis. While the invention has been described by means of specific embodiments and applications thereof, it is understood that numerous modifications and variations could be made thereto by those skilled in the art without departing from the spirit and scope of the invention. It is therefore to be understood that within the scope of the claims, the invention may be practiced otherwise than as specifically described herein.