Abstract:
Applicant has proposed a combination of the subretinal and epiretinal methods by placing the electronics external to the eye, entering the eye through the pars plana and the piercing the retina (retinotomy) from inside the eye to stimulate subreintally. The present invention is an improved electrode array for subretinal stimulation. A hard polymer such as polyimide is biocompatible and strong for supporting an electrode array and supporting traces in a thin flex circuit array. In the present invention applicant takes advantage of the sharp nature of thin polyimide making a point on the end of the electrode array. This allows the flexible circuit electrode array to be both electrode array and surgical tool to cut the retinal and slide the array under the retina in a single action.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This claims the benefit of U.S. Provisional Application No. 60/718,779, “Transretinal Flexible Circuit Electrode Array”, filed Sep. 19, 2005, the disclosures of all are incorporated herein by reference.  
         [0002]     This application is a Continuation-In-Part of U.S. application Ser. No. 10/393,887, “Transretinal Implant and Method of Manufacture”, filed Mar. 21, 2003, the disclosure of which is incorporated herein by reference.  
         [0003]     This application is a Continuation-In-Part of U.S. application Ser. No. 11/413,689, “Flexible circuit electrode array”, filed Apr. 28, 2006, which is a Continuation-In-Part of U.S. application Ser. No. 11/207,644, “Flexible circuit electrode array”, filed Aug. 19, 2005 which claims the benefit of U.S. Provisional Application No. 60/676,008, “Thin Film Electrode Array”, filed Apr. 28, 2005, the disclosures of all are incorporated herein by reference. 
     
    
     GOVERNMENT RIGHTS NOTICE  
       [0004]     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  
       [0005]     The present invention is generally directed to neural stimulation and more specifically to an improved electrode array for subretinal stimulation.  
       BACKGROUND OF THE INVENTION  
       [0006]     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 prostheses 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.  
         [0007]     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.  
         [0008]     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 apparatus to aid the visually impaired. Specifically, great effort has been expended in the area of intraocular retinal prosthetic 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.  
         [0009]     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.  
         [0010]     Based on this mechanism, it is possible to input information into the nervous system by coding the sensory 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.  
         [0011]     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, control the electronic field distribution and avoid undue compression of the visual neurons.  
         [0012]     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.  
         [0013]     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 μA 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).  
         [0014]     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.  
         [0015]     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. Retinal tacks are one way to attach a retinal electrode array to the retina. U.S. Pat. No. 5,109,844 to de Juan describes a flat electrode array placed against the retina for visual stimulation. U.S. Pat. No. 5,935,155 to Humayun describes a retinal prosthesis for use with the flat retinal array described in de Juan.  
       SUMMARY OF THE INVENTION  
       [0016]     Applicant has proposed a combination of the subretinal and epiretinal methods by placing the electronics external to the eye, entering the eye through the pars plana and then piercing the retina (retinotomy) from inside the eye to stimulate subretinally.  
         [0017]     The present invention is an improved electrode array for subretinal stimulation. A hard polymer such as polyimide is biocompatible and strong for supporting an electrode array and supporting traces in a thin flex circuit array. The applicants describe the disadvantage of material such as polyimide is that when made thin, it can cut delicate retina tissue. The application further describes methods of protecting the retina. In the present invention applicant takes advantage of the sharp nature of thin polyimide making a point on the end of the electrode array. This allows the flexible circuit electrode array to be both electrode array and surgical tool to cut the retinal and slide the array under the retina in a single action.  
         [0018]     The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a perspective view of the implanted portion of the preferred retinal prosthesis.  
         [0020]      FIG. 2  depicts the flexible circuit array before it is folded and attached to the implanted portion.  
         [0021]      FIG. 3  depicts the flexible circuit array folded.  
         [0022]      FIG. 4  is a fundus photo and flourescein angiogram after 3 month of the preferred trans-retinal implant in a rabbit.  
         [0023]      FIG. 5  illustrates a cross-sectional view of an eye showing the placement of the retinal implant and associated electronics.  
         [0024]      FIG. 6  illustrates a cross-sectional view of a retina showing the tissue layers and placement of the retinal implant in the retina for electrical stimulation of the retina.  
         [0025]      FIG. 7  illustrates a cross-sectional view of an eye showing placement of the retinal implant for drug delivery.  
         [0026]      FIG. 8  illustrates a cross-sectional view of an eye showing the placement of the subretinal implant.  
         [0027]      FIG. 9  illustrates a cross-sectional view of an eye showing the placement of the subretinal implant.  
         [0028]      FIG. 10  illustrates a cross-sectional view of a retina showing the tissue layers and placement of the retinal implant in the retina for drug delivery 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]     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.  
         [0030]      FIG. 1  shows a perspective view of the implanted portion of the preferred retinal prosthesis. A flexible circuit  1  includes a flexible circuit electrode array  10 . The flexible circuit electrode array  10  is electrically coupled by a flexible circuit cable  12 , which pierces first the sclera, then the retina and is electrically coupled to an electronics package  14 , external to the sclera. The flexible circuit  1  further forms a point  24  at its end, beyond the flexible circuit electrode array  10 . While the point  24  aids in passing the flexible circuit  1  through the sclerotomy, it is particularly useful for passing the flexible circuit  1  through the retina. While the sclera is relatively tough and requires a sclerotomy, the retina is very soft. The point  24  can cut the retina (retinotomy) as in is inserted. This minimizes the size of the retinotomy, reduces the chances of hemorrhage or retina detachment, and simplifies the implant surgery.  
         [0031]     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  16  may be made from a flexible circuit polymer sandwich with wire traces deposited between layers of flexible circuit 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  18  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  22  can better support an oval shaped coil.  
         [0032]     The flexible circuit  1  is a made by the following process. First, a layer of polymer (such as polyimide, fluoro-polymers, silicone or other polymers) is applied to a support substrate (not part of the array) such as glass. Layers may be applied by spinning, meniscus coating, casting, sputtering or other physical or chemical vapor deposition, or similar process. Subsequently, a metal layer is applied to the polymer. The metal is patterned by photolithographic process. Preferably, a photo-resist is applied and patterned by photolithography followed by a wet etch of the unprotected metal. Alternatively, the metal can be patterned by lift-off technique, laser ablation or direct write techniques.  
         [0033]     It is advantageous to make this metal thicker at the electrode and bond pad to improve electrical continuity. This can be accomplished through any of the above methods or electroplating. Then, the top layer of polymer is applied over the metal. Openings in the top layer for electrical contact to the electronics package  14  and the electrodes may be accomplished by laser ablation or reactive ion etching (RIE) or photolithograph and wet etch. Making the electrode openings in the top layer smaller than the electrodes promotes adhesion by avoiding delaminating around the electrode edges.  
         [0034]     The implanted portion of the retinal prosthesis includes the additional feature of a gentle twist or fold  48  in the flexible circuit cable  12 , where the flexible circuit cable  12  passes through the sclera (sclerotomy). The twist may be a simple sharp twist, or fold  48 ; or it may be a longer twist, forming a tube. While the tube is rounder, it reduces the flexibility of the flexible circuit. A simple fold  48  reduces the width of the flexible circuit with only minimal impact on flexibility.  
         [0035]     Further, silicone or other pliable substance may be used to fill the center of the tube or fold  48  formed by the twisted flexible circuit cable  12 . Further it is advantageous to provide a sleeve or coating  50  that promotes healing of the sclerotomy. Polymers, such as polyimide, which may be used to form the flexible circuit cable  12  and flexible circuit electrode array  10 , are generally very smooth and do not promote a good bond between the flexible circuit cable  12  and scleral tissue. A sleeve or coating of polyester, collagen, silicone, Gore-tex or similar material would bond with scleral tissue and promote healing. In particular, a porous material will allow scleral tissue to grow into the pores promoting a good bond.  
         [0036]     It is also advantageous to create a reverse curve or service loop in the flexible circuit cable  12  of the flexible circuit electrode array to gently lift the flexible circuit cable  12  off the retina and curve it away from the retina, before it pierces the sclera at a sclerotomy. This service loop reduces the likelihood of any stress exerted extraocularly from being transmitted to the electrode region and retina. It also provides for accommodation of a range of eye sizes.  
         [0037]     With existing technology, it is necessary to place the implanted control electronics outside of the sclera, while a retinal flexible circuit electrode array must be inside the sclera in order to contact the retina. The sclera is cut through at the pars plana, forming a sclerotomy, and the flexible circuit passed through the sclerotomy. A flexible circuit is thin but wide. The more electrode wires, the wider the flexible circuit must be. It may be difficult to seal a sclerotomy over a flexible circuit wide enough to support enough wires for a high resolution array. A narrow sclerotomy is preferable.  
         [0038]      FIG. 2  shows the flexible circuit electrode array prior to folding and attaching the array to the electronics package  14 . At one end of the flexible circuit cable  12  is an interconnection pad  52  for connection to the electronics package  14 . At the other end of the flexible circuit cable  12  is the flexible circuit electrode array  10 . Further, a point  24  is provided at the end of the flexible circuit electrode array  10 . The flexible circuit cable  12  is formed in a dog leg pattern so than when it is folded at fold  48  it effectively forms a straight flexible circuit cable  12  with a narrower portion at the fold  48  for passing through the sclerotomy.  
         [0039]      FIG. 3  shows the flexible circuit electrode array after the flexible circuit cable  12  is folded at the fold  48  to form a narrowed section. The flexible circuit cable  12  may include a twist or tube shape as well. With a retinal prosthesis as shown in  FIG. 1 , the bond pad  52  for connection to the electronics package  14  and the flexible circuit electrode array  10  are on opposite side of the flexible circuit. This requires patterning, in some manner, both the base polymer layer and the top polymer layer. By folding the flexible circuit cable  12  of the flexible circuit electrode array  10 , the openings for the bond pad  52  and the electrodes are on the top polymer layer and only the top polymer layer needs to be patterned. Further, a point  24  is provided at the end of the flexible circuit electrode array  10 . The point  24  shown in  FIGS. 2 and 3  is formed throughout the hole thickness of the array. The array may contain at least one bottom layer containing at least one polymer, copolymer, blockcopolymer or mixtures thereof and at least one top layer containing at least one polymer, copolymer, blockcopolymer or mixtures thereof. The polymer may be polyimide, silicone, PEEK polymer, a repeat unit that comprises of oxy-1,4-phenylenoeoxy-1,4-phenylene-carbonyl-1,4-phenylene, parylene or mixtures thereof.  
         [0040]     Also, since the narrowed portion of the flexible circuit cable  12  pierces the sclera, shoulders formed by opposite ends of the narrowed portion help prevent the flexible circuit cable  12  from moving through the sclera. It may be further advantageous to add ribs or bumps of silicone or similar material to the shoulders to further prevent the flexible circuit cable  12  from moving through the sclera.  
         [0041]     Further it is advantageous to provide a suture tab  56  in the flexible circuit body near the electronics package to prevent any movement in the electronics package from being transmitted to the flexible circuit electrode array  10 . Alternatively, a segment of the flexible circuit cable  12  can be reinforced to permit it to be secured directly with a suture. The retina tack (not shown) is placed through an attachment point  54  to hold the flexible circuit electrode array  10  to the retina. A stress relief  55  can be made of a softer polymer than the flexible circuit  1 .  
         [0042]      FIG. 4  shows a fundus photo and flourescein angiogram after 3 month of the preferred flexible circuit  1  implant in a rabbit. It is shown that the point  24  of the flexible circuit  1  cuts the retina as it is inserted. 15 rabbits were chronically implanted for over three months each with polyimide flexible circuit  1  which were from 0.3 mm to 0.7 mm, preferably about 0.5 mm wide and from 3.5 mm to 4.5 mm, preferably about 4 mm long using the preferred trans-retinal surgical approach which included laser treatment around the retinotomy site. The flexible circuit  1  were inserted under the retina and left with a portion of the flexible circuit cable  12  sticking out into the vitreous. In an actual device, according the present invention, the flex circuit cable  12  of  FIG. 4  would be attached to an electronics package  14  as described above.  
         [0043]      FIG. 5  provides a cross-sectional view of a preferred embodiment of the eye  2  with a retinal implant  19  placed subretinally. The current invention involves the use of an electronic device, a retinal implant  19  that is capable of mimicking the signals that would be produced by a normal inner retinal photoreceptor layer. When the device is implanted subretinally between the inner and outer retinal layers, it will stimulate the inner layer to provide significantly useful formed vision to a patient who&#39;s eye no longer reacts to normal incident light on the retina  20 . Patient&#39;s having a variety of retinal diseases that cause vision loss or blindness by destruction of the vascular layers of the eye, including the choroid, choriocapillaris, and the outer retinal layers, including Bruch&#39;s membrane and retinal pigment epithelium. Loss of these layers is followed by degeneration of the outer portion of the inner retina, beginning with the photoreceptor layer. The inner retina, composed of the outer nuclear, outer plexiform, inner nuclear, inner plexiform, ganglion cell and nerve fiber layers, may remain functional. Functioning of the inner retina allows electrical stimulation of this structure to produce sensations of light or even vision.  
         [0044]     The biocompatible retinal implant  19  is attached by an electrically conductive cable or lead wire  25  that is also biocompatible, to a control electronics  14  package that contains suitable electronics to generate an electrical signal that is transmitted along a lead wire  25  to the retinal implant, which stimulates the retina  11 . The lead wire  25  passes transretinally through retinal incision  13  and enters the vitreous cavity  9 . The lead wire  25  then passes transsclera at sclera incision  13  that passes through the sclera at a location near the front of the eye where there is no retina  11 .  
         [0045]     The eye  2  has a cornea  4 , lens  8 , and vitreous cavity  9  through which light normally passes, prior to striking the retina  11  and causing vision. The eye  2  has an outer layer, called the sclera  6 , and a nutrient rich layer, called the choroid  18 , that is located between the retina  11  and the sclera  6 .  
         [0046]     In a preferred embodiment, the retinal implant  20  is located subretinally near the fovea  15  to provide good electrical contact between the retinal implant  19  and the retina  11 . The lead wire  25 , which is attached to the retinal implant  19 , proceeds transretinally through retina  11  via retinal incision  23 . Passing the lead wire into the vitreous cavity  9  via the retinal incision  23  avoids disrupting the delicate choroid  17 , and thereby avoids interfering with the supply of nutrients to the retina  11 . The lead wire  25  passes through the vitreous cavity to a point near the front of the eye  2  where it traverses transsclera via an incision  13  through the sclera  6  at a point where the retina  11  and choroid  17  are not present, thereby further avoiding disruption to the blood supply, oxygen, and nutrients that are needed to sustain the retina  11 . While the choroid  17  does extend to this region of the eye near the lens  8 , called the pars plana, choroid  17  bleeding will not damage the retina  11 , and is far less likely to spread to the central retina  11 , called the macula, which is the area of most sensitive vision, while choroid  17  bleeding under the retina  11  can track along the retina  11  and end up damaging the macular region near the fovea  19  of the retina  11 .  
         [0047]     The control electronics  14  are located outside the eye  2  and are attached to lead wire  25 . The control electronics  14  are preferably attached to the sclera  6  by sutures. In alternative embodiments, the control electronics  14  are located distant from the eye  2 .  
         [0048]     A perspective cross-sectional view of the retina and outer wall of the eye is presented in  FIG. 6 . Moving from the inside of the eye outward, the structure of the eye is encountered as follows: internal limiting membrane  51 , axons  53 , ganglion and amacrine cell layer  55 , inner plexiform  57 , inner nuclear layer  58 , outer plexiform layer  60 , bipolar cell layer  62 , photoreceptor cell layer  64 , retinal pigment epithelium  68 , Bruck&#39;s membrane  70 , choriocapillaris  72 , choroid  74 , and the outer coat or sclera  76 .  
         [0049]     The inner retina  78  is generally the structures from the internal limiting membrane  50  to the photoreceptor cell layer  64 . The outer retinal layer is the retinal pigment epithelium  68  and Bruck&#39;s membrane  70 .  
         [0050]     A subretinal implant position  80  is located between the photoreceptor cell layer  64  and the retinal pigment epithelium  68 . In a preferred embodiment, the retinal implant  66  is surgically implanted in the subretinal implant position  80 .  
         [0051]     In a preferred embodiment, the retinal implant  66  is biocompatible and contains a number of arrayed electrodes  84 , which are electrically stimulated by an outside source to stimulate the inner retinal layer  78 , thereby to provide significantly useful formed vision. It is preferred that the electrodes  84  are located on the surface of the retinal implant  66  that faces the front of the eye, to stimulate the inner retinal layer  78 .  
         [0052]     A cross-sectional view of the eye  102  and retinal implant  132  is presented in  FIG. 7 . In this embodiment of the invention, drugs are delivered by transfer from drug reservoir  130  to retinal implant  132 , where the drugs are released subretinally for treatment of the tissue of the eye  2  and especially the retinal tissue. This device is particularly advantageous for treatment of chronic issues. A further advantage is that the quantity of drugs required and released to the eye is minimized by releasing the drugs in near proximity to the area of the eye  102  that requires treatment.  
         [0053]     In a preferred embodiment, the drugs are transferred from drug reservoir  130  via delivery conduit  128 , which is preferably a tube, to retinal implant  132 . While the drugs may be pumped or delivered by other known means, it is preferable that they be delivered electrophoretically.  
         [0054]     The structure of the eye  2 , as shown in  FIG. 7 , presents a cornea  104  at the front of the eye with a lens  108  behind. The sclera  106  is on the outside of the eye and the choroid  118  is inside the eye  2  between the retina  112  and sclera  106 .  
         [0055]     The retinal implant  132  is implanted subretinally, preferably near the back of the eye. It is shown near the fovea  113 , in  FIG. 7 , but may be located at other subretinal locations, as desired. The drug delivery conduit  128  connects the retinal implant  132  with the drug reservoir  130 . The conduit  128  passes transretinally through retinal incision  124  and enters the vitreous cavity  110 . The conduit  128  then passes transsclera at sclera incision  114  that passes through the sclera at a location near the front of the eye where there is no retina  112 , thereby avoiding damage to the nutrient rich choroid  118  and avoiding disruption of the blood supply to the retina  112 .  
         [0056]     An alternative embodiment of a retinal implant to enable vision restoration is presented in  FIG. 8 , wherein a cross-section of the eye is presented showing the lens  208 , retina  212 , sclera  206 , and fovea  213 . U.S. Pat. No. 5,935,155, issued to Humayun, et al., the &#39;155 patent, describes a similar visual prosthesis and method of use. In this embodiment, the retinal implant  220  is implanted subretinally. A primary coil  232  is located preferably either in an eyeglass lens frame or in a soft contact lens. This coil  232  is used to inductively couple the radio frequency encoded image signal to the secondary coil  230  that, in this embodiment, is implanted behind the iris of the eye. The control electronics  222  is placed in a hermetically sealed package and is coupled to a secondary coil  230  by a coil lead  223  that pierces the sclera  206  at a point near the lens  208  where there is no retina  212 . The control electronics  222  is attached to the outside of the sclera  206 . A lead wire  226  coupling the control electronics  222  to the retinal implant  220  passes transsclera at a point where there is no retina, preferably near the lens  208 . The lead wire  226  passes inside the eye, preferably along the interior wall of the eye, and pierces the retina to pass transretinal to couple the control electronics  222  to the retinal implant  220 . This invention is an improvement over that disclosed by the &#39;155 patent because the retinal implant is subretinal rather than epiretinal, thereby facilitating stimulation of the retinal tissue.  
         [0057]     A further alternative embodiment of a retinal implant to enable vision restoration is presented in  FIG. 9 . The &#39;155 patent discloses a similar invention, wherein the retinal implant  220  is placed subretinally. In this embodiment, the secondary  230  is attached to the sclera  206  instead of being implanted within the eye. As with the control electronics  222 , the attachment of the secondary coil  230  to the sclera  206  may be by suturing or other appropriate means, as discussed in the &#39;155 patent. In this way, only the lead wire  226  which attaches the control electronics  222  to the retinal implant  220  mounted subretinally below retina  212  is required to pierce the sclera  206 . The extra-ocular attachment of the control electronics  222  allows increased access to this circuitry that eases the replacement or updating of these components.  
         [0058]      FIG. 10  presents a perspective cross-sectional view of the retina and outer wall of the eye. The tissue layers from the inside of the eye outward are the internal limiting membrane  150 , axons  152 , ganglion and amacrine cell layer  154 , inner plexiform  156 , inner nuclear layer  158 , outer plexiform layer  160 , bipolar cell layer  162 , photoreceptor cell layer  164 , retinal pigment epithelium  168 , Bruck&#39;s membrane  170 , choriocapillaris  172 , choroid  174 , and sclera  176 .  
         [0059]     The inner retinal layer  178  is comprised of tissue from the internal limiting membrane  150  to the photoreceptor cell layer  164 . The outer retinal layer  182  consists of the retinal pigment epithelium  168  and Bruck&#39;s membrane  170 .  
         [0060]     Between the inner retinal layer  178  and outer retinal layer  182 , is the subretinal implant position  180  in which retinal implant  186  is surgically located.  
         [0061]     The retinal implant contains a number of orifices  188  through with the drug is released into the surrounding retinal tissue. The orifices  188  are preferably uniformly presented on both the inner and outer surfaces as well as on the edges of the retinal implant  186 . However, the orifices  188  may be preferentially oriented in the retinal implant  186  to selectively release the drug on or near a desired tissue or location.  
         [0062]     The invention relates to an implantable device to affect an eye, the eye having a retina, a sclera, and a vitreous cavity, said device comprising:  
         [0063]     a retinal implant that is positioned subretinally;  
         [0064]     said retinal implant comprising at least one electrode connected with a stimulating source;  
         [0065]     at least one connection with said stimulating source and with said at least one electrode, wherein said connection is suitable to pass transretinally into the vitreous cavity of the eye;  
         [0066]     said connection suitably designed to pass through the sclera at a point where there is no retina; and  
         [0067]     said stimulating source is suitable to be located outside the sclera.  
         [0068]     The retinal implant is configured to enable electrical stimulation of a retina of an eye to produce artificial vision.  
         [0069]     The stimulating source is comprised of a source of electrical signal. The connection is comprised of an electrical lead. At least one electrode that is configured to pass an electrical signal to the retina. The retinal implant that is positioned subretinally is suitable to be positioned between the photoreceptor cell layer and the retinal pigment epithelium. The stimulating source comprises electrical coupling with a secondary coil, which receives electromagnetic signals from a primary coil, said primary coil located outside the sclera. The secondary coil is suitable to be located inside the eye. The secondary coil is suitable to be located outside the sclera.  
         [0070]     The invention relates to an implantable device to deliver drugs to an eye, the eye having a retina, a sclera, and a vitreous cavity, said device comprising:  
         [0071]     a retinal implant that is positioned subretinally for drug release;  
         [0072]     said retinal implant comprising a drug delivery device connected with a drug reservoir;  
         [0073]     at least one connection between said drug reservoir and said retinal implant, wherein said connection is suitable to pass transretinally into the vitreous cavity of the eye;  
         [0074]     said connection being suitable to pass through the sclera at a point where there is no retina; and  
         [0075]     said drug reservoir is located outside the eye.  
         [0076]     The implantable device delivers the drugs electrophoretically. The connection comprises a tube. The retina additionally is comprised of a photoreceptor cell layer and a retinal pigment epithelium wherein said retinal implant that is positioned subretinally is suitable to be positioned between the photoreceptor cell layer and the retinal pigment epithelium.  
         [0077]     The invention relates to an artificial retinal device to electrically stimulate a retina of an eye to produce artificial vision, the eye having a sclera, and a vitreous cavity, said artificial retinal device comprising:  
         [0078]     a retinal implant that is positioned subretinally;  
         [0079]     said retinal implant comprising at least one stimulating electrode connected with an electrical source that is located outside the eye;  
         [0080]     at least one electrical lead connected with said electrical source and with said at least one stimulating electrode, wherein said electrical lead is suitable to pass transretinally into the vitreous cavity of the eye; and  
         [0081]     said electrical lead passing through the sclera at a point where there is no retina.  
         [0082]     The electrical source is suitable to affix to the sclera of the eye with sutures. The electrodes are facing the retinal. The retina additionally is comprised of a photoreceptor cell layer and a retinal pigment epithelium wherein said retinal implant that is positioned subretinally is suitable to be positioned between the photoreceptor cell layer and the retinal pigment epithelium.  
         [0083]     The invention relates to an implantable device drug delivery device to deliver drugs for treatment to affect an eye, the eye having a retina, a sclera, and a vitreous cavity, said device comprising:  
         [0084]     a retinal implant that is positioned subretinally;  
         [0085]     said retinal implant comprising at least one orifice connected with a drug reservoir;  
         [0086]     at least one delivery conduit connected with said drug reservoir and with said at least one orifice, wherein said delivery conduit is suitable to pass transretinally into the vitreous cavity of the eye;  
         [0087]     said delivery conduit suitably designed to pass through the sclera at a point where there is no retina; and  
         [0088]     said drug reservoir is suitable to be located outside the sclera.  
         [0089]     The implant releases said drugs electrophoretically. The delivery conduit is a tube that transfers said drugs from said drug reservoir to said retinal implant. The drug is suitable to stimulate living tissue. The retinal implant that is positioned subretinally is suitable to be positioned between the photoreceptor cell layer and the retinal pigment epithelium. The implantable device comprises an electrophoretic drug delivery device. The retinal implant is configured to enable drug stimulation of a retina of an eye to produce artificial vision.  
         [0090]     The invention relates to a method for producing an artificial retinal device suitable to electrically stimulate a retina of an eye to produce artificial vision, the eye having a sclera, and a vitreous cavity, said method comprising the steps of:  
         [0091]     selecting a biocompatible retinal implant;  
         [0092]     placing at least one stimulating electrode in said retinal implant that is suitable for electrically stimulating the retina;  
         [0093]     connecting an electrical lead to said stimulating electrode;  
         [0094]     adapting said electrical lead to pass transretinally into the vitreous cavity of the eye;  
         [0095]     attaching said electrical lead to an electrical source that is located outside the eye; and  
         [0096]     passing said electrical lead through the sclera at a point where there is no retina.  
         [0097]     The invention relates to a method for producing artificial vision in an eye using an artificial retinal device, the eye having a sclera, a retina, and a vitreous cavity, wherein said artificial retinal device comprises a retinal implant further comprising at least one stimulating electrode in said retinal implant, said stimulating electrode connected with an electrical source, at least one electrical lead connected with said electrical source and said electrode, the method comprising the steps of:  
         [0098]     adapting said retinal implant to be positionable in the subretinal position in the eye;  
         [0099]     adapting said electrical lead to be suitable to pass transretinally through the retina of the eye into the vitreous cavity; and  
         [0100]     adapting said electrical lead to be suitable to pass through the sclera at a point where there is no retina.  
         [0101]     The method comprises the step of attaching said electrical source to the sclera by sutures.  
         [0102]     The method further comprises the step of positioning said electrodes to face the retina.  
         [0103]     The invention relates to a visual prosthesis, comprising:  
         [0104]     means for perceiving a visual image where said means is suitable to be located outside the eye of a user, said means producing a visual signal output in response thereto;  
         [0105]     retinal tissue stimulation means adapted to be operatively attached to a retina of a user, where said retinal stimulation means is suitable to be located below the retina of a user; and  
         [0106]     wireless visual signal communication means for transmitting said visual signal output to said retinal tissue stimulation means.  
         [0107]     The invention relates to a method of at least partially restoring vision to a user who suffers from photoreceptor degenerative retinal conditions of the eye, comprising the steps of:  
         [0108]     perceiving a visual image and producing a visual signal output in response thereto;  
         [0109]     wirelessly transmitting the visual signal output into the eye of a user; and  
         [0110]     stimulating retinal tissue of the user by means of an electrode, that is suitable to be placed below the retina of a user, in accordance with the visual signal output.  
         [0111]     The invention relates to a flexible circuit electrode array comprising: 
    a polymer base layer;     metal traces deposited on said polymer base layer, including electrodes suitable to stimulate neural tissue; and     said polymer base layer and said metal traces are embedded in a body having a generally oval shape in the plane of the retina, said oval shaped body being curved such that it substantially conforms to the spherical curvature of the retina of the recipient&#39;s eye.    
 
         [0115]     The flexible circuit electrode array comprises at least one mounting aperture in said body for attaching the electrode array to the retina with a tack. The oval shaped body has a radius of spherical curvature, which is smaller than the radius of the curvature of the eye. The oval shaped body is made of a soft polymer containing silicone having hardness of about 50 or less on the Shore A scale as measured with a durometer. The flexible circuit cable portion has an angle of about 45° to about 180°. The flexible circuit cable portion has a bend with an angle of about 60° to about 120°. The flexible circuit cable portion has a bend with an angle of about 45° to about 180°. The flexible circuit cable portion has a bend with an angle of about 60° to about 120°. The flexible circuit cable portion has a fold within the attached flexible circuit electrode array with an angle of about 1° to about 180°. The flexible circuit cable portion has a fold within the attached flexible circuit electrode array with an angle of about 20° to about 90°. The flexible circuit cable portion has a horizontal angle within the attached flexible circuit electrode array of about 1° to about 90°. The flexible circuit cable portion has a horizontal angle within the attached flexible circuit electrode array of about 10° to about 45°. The flexible circuit cable portion comprises at least one grooved or rippled pad for capturing a mattress suture. The flexible circuit electrode array is positioned on the surface of the body having a generally oval shape. The soft insulating material is positioned on the surface between said electrodes. The film containing a soft polymer is applied on said flexible circuit cable portion. The film containing a soft polymer contains silicone. The film containing a soft polymer comprises a ladder like structure. The film containing a soft polymer contains beads and/or bumpers.  
         [0116]     The invention relates to a method of making a flexible circuit electrode array comprising: 
    depositing a polymer base layer;     depositing metal on said polymer base layer;     patterning said metal to form metal traces;     depositing a polymer top layer on said polymer base layer and said metal traces; and     heating said flexible circuit electrode array in a mold to form a three dimensional shape in said flexible circuit electrode array.    
 
         [0122]     The method further comprising the steps of heating said flexible circuit electrode array in successively smaller molds. The step of depositing said polymer base layer and said polymer top layer is depositing polyimide. The step of depositing said polymer base layer and said polymer top layer is depositing silicone. The step of depositing said polymer base layer and said polymer top layer is depositing fluoro-polymer. The method further comprising forming a twist in a flexible circuit cable portion of said flexible circuit electrode array.  
         [0123]     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.  
         [0124]     Accordingly, what has been shown is an improved method making a neural electrode array and improved method of stimulating neural tissue. 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.