Abstract:
The present invention is a flexible circuit electrode array for improved layer adhesions where the metal conductors overlap the polymer insulator. The steps to build the flexible circuit are as follows. Deposit a base polymer layer. Deposit a conductive trace over the base polymer layer. Deposit a top polymer layer over the trace and prepare a void in the top polymer layer smaller than the surface of the trace. Deposit an electrode on the trace through the void with a periphery larger than, and overlapping the void.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional application of U.S. patent application Ser. No. 11/331,625, filed Jan. 13, 2006, for Flexible Circuit Electrode Array for Improved Layer Adhesion, which is a divisional application of U.S. patent application Ser. No. 11/293,300, filed Dec. 1, 2005, for Visual Prosthesis for Improved Circadian Rhythms and Method of Improving the Circadian Rhythms, now U.S. Pat. No. 8,068,913, which claims the benefit of U.S. Provisional Application No. 60/633,190, Visual Prosthesis for Improved Circadian Rhythms, filed Dec. 3, 2004, the disclosure of which is incorporated herein by reference. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR  DEVELOPMENT 
       [0002]    This invention was made with government support under grant No. R24EY12893-01, which has been awarded by the National Institutes Health. The government has certain rights in the invention. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    The present invention is generally directed to neural stimulation and more specifically to neural stimulation of the visual system for improved circadian rhythms and a method of improving the circadian rhythms. 
         [0005]    2. 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 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. 
         [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 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. 
         [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 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 (epiretial). 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. 
         [0012]    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 .mu.A 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). 
         [0013]    In U.S. Pat. No. 3,699,970 “Striate Cortex Stimulator” to Giles Skey Brindley et al. an implantable device is disclosed comprising a plurality of electrodes for stimulating the striate cortex. 
         [0014]    In U.S. Pat. No. 4,487,652 “Slope. Etch of Polyimide” to Carl W. Amgren a semiconductor having an insulating layer overlying a metal layer is disclosed, wherein the insulator comprises an upper oxide layer, an intermediate polyimide layer, and a lower oxide layer in contact with the metal layer, a method for etching a via from an upper surface of the polyimide layer to the metal layer comprising the steps of applying photoresist; etching an opening from an upper surface of the photoresist layer to the upper oxide layer at a location for forming the via so that an upper surface of the upper oxide layer is exposed at the via location; heating the photoresist to cause a more gradual slope of the photoresist layer from the upper surface of the upper oxide layer at the via location to the upper surface of the photoresist layer; applying reactive ion etchant with a predetermined selectivity between photoresist and oxide to transfer the slope of the photoresist layer to the upper oxide layer at a predetermined ratio; and applying a reactive ion etchant with a predetermined selectivity between oxide and polyimide to transfer the slope of the upper oxide layer to the polyimide layer at a predetermined ratio, whereby the lower oxide layer is simultaneously etched to expose the metal layer at the via location. 
         [0015]    In U.S. Pat. No. 4,573,481 “Implantable Electrode Array” to Leo A. Bullara an electrode assembly for surgical implantation on a nerve of the peripheral nerve system is disclosed. 
         [0016]    In U.S. Pat. No. 4,628,933 “Method and Apparatus for Visual Prosthesis” to Robin P. Michelson a visual prosthesis for implantation in the eye in the optical pathway thereof is disclosed. 
         [0017]    In U.S. Pat. No. 4,837,049 “Method of Making an Electrode Array” to Charles L. Byers et al. a very small electrode array which penetrates nerves for sensing electrical activity therein or to provide electrical stimulation is disclosed. 
         [0018]    In U.S. Pat. No. 4,996,629 “Circuit Board with Self-Supporting Connection Between Sides” to Robert A. Christiansen et al. a copper supporting sheet is disclosed having vias for connecting semiconductor chips to surface mount components. A laminate of polyimide has vias corresponding to the supporting layer vias with copper covering those vias. 
         [0019]    In U.S. Pat. No. 5,108,819 “Thin Film Electrical Component” to James W. Heller a thin film electrical component is disclosed comprising a rigid glass carrier plate, a substrate bonded to the rigid glass carrier plate, the substrate comprising a polyimide establishing a bond with the rigid glass carrier plate that is broken upon immersion of the substrate and the rigid glass carrier plate in one of a hot water bath and a warm temperature physiologic saline bath to release the polymer from attachment to the rigid glass carrier plate, and means for providing an electrical circuit, the providing means being bonded to the substrate and undisrupted during release of the substrate from attachment to the rigid glass carrier plate. 
         [0020]    In U.S. Pat. No. 5,109,844 “Retinal Microstimulation” to Eugene. de Juan Jr. et al. a method for stimulating a retinal ganglion cell in a retina without penetrating the retinal basement membrane at the surface of the retina is disclosed. 
         [0021]    In U.S. Pat. No. 5,178,957 “Noble Metal-Polymer Composites and Flexible Thin-Film Conductors Prepared Therefrom” to Vasant V. Kolpe a composite article is disclosed comprising a polymeric support selected from the group consisting of a polyimide, polyethylene terephthalate, and polyester-ether block copolymer having a noble metal deposited directly onto at least one surface, wherein the deposited metal exhibits a peel force of at least about 0.05 kg per millimeter width after 24 hour boiling saline treatment. 
         [0022]    In U.S. Pat. No. 5,215,088 “Three-Dimensional Electrode Device” to Richard A. Norman et al. a three-dimensional electrode device for placing electrodes in close proximity to cell lying at least about 1000 microns below a tissue surface is disclosed. 
         [0023]    In U.S. Pat. No. 5,935,155 “Visual Prosthesis and Method of Using Same” to Mark S. Humayun et al. a visual prosthesis is disclosed comprising a camera for receiving a visual image and generating a visual signal output, retinal tissue stimulation circuitry adapted to be operatively attached to the user&#39;s retina, and wireless communication circuitry for transmitting the visual signal output to the retinal tissue stimulation circuitry within the eye. 
         [0024]    In U.S. Pat. No. 6,071,819 “Flexible Skin Incorporating MEMS Technology” to Yu-Chong Tai a method of manufacturing a flexible microelectronic device is disclosed comprising first etching a lower side of a wafer using a first caustic agent; depositing a first layer of aluminum on an upper side of the wafer; patterning the first layer of aluminum; depositing a first layer of polyimide on the upper side of the wafer, covering the first layer of aluminum; depositing a second layer of aluminum on the upper side of the wafer, covering the first layer of polyimide; depositing a second layer of polyimide on the upper side of the wafer, covering the second layer of aluminum; depositing a third layer of aluminum on the lower side of the wafer; patterning the third layer of aluminum; second etching the lower side of the wafer using the third layer of aluminum as a mask and the first layer of aluminum as an etch stop and using a less caustic agent than the first caustic agent, such that the wafer is divided into islands with gaps surrounding each island; and depositing a third layer of polyimide on the lower side of the wafer, such that the gaps are at least partially filled. 
         [0025]    In U.S. Pat. No. 6,324,429 “Chronically Implantable Retinal Prosthesis” to Doug Shire et al. an apparatus is disclosed which is in contact with the inner surface of the retina and electrically stimulates at least a portion of the surface of the retina. 
         [0026]    In U.S. Pat. No. 6,374,143 “Modiolar Hugging Electrode Array” to Peter G. Berrang et al. a cochlear electrode array for stimulating auditory processes is disclosed. 
         [0027]    In U.S. Pat. No. 6,847,847 “Retina Implant Assembly and Methods for Manufacturing the Same” to Wilfried Nisch et al. a retina implant is disclosed comprising a chip in subretinal contact with the retina and a receiver coil for inductively coupling there into electromagnetic energy. 
         [0028]    In U.S. patent application Ser. No. 20010037061 A1, “Microcontact structure for neuroprostheses for implantation on nerve tissue and method therefore” to Rolf Eckmiller et al. a four layer microcontact structure is disclosed in which the active connection between the microcontact structure and the nerve tissue is brought about by electrical stimulation. The layer adjacent to the nerve tissue to be stimulated is composed of the polymer polyimide and contains penetrating electrodes made of platinum which fauns the adjoining layer. There follows a further layer of the polyimide and a layer of the polymer polyurethane. Polyurethane has the property of thermal expansion relative to polyimide. 
         [0029]    In U.S. patent application Ser. No. 2003/0158588 A1 “Minimal Invasive Retinal Prosthesis” to John F. Rizzo et al. a retinal prosthesis is disclosed comprising an RF coil attached to the outside of and moving with an eye to receive power from an external power source; electronic circuitry attached to and moving with the eye and electrically connected to the RF coil; a light sensitive array electrically connected to the electronic circuitry and located within the eye for receiving incident light and for generating an electrical signal in response to the incident light; and a stimulating array abutting a retina of the eye and electrically connected to the electronic circuitry to stimulate retinal tissue in response to the electrical signal from the light sensitive array. A supporting silicone substrate has a polyimide layer spun onto its surface and cured. The copper or chrome/gold conducting layer is then added and patterned using wet chemical etching or a photoresist lift-off process. Next, a second polyimide layer is spun on, and the regions where circuit components are to be added are exposed by selective dry etching or laser ablation of the upper polyimide layer in the desired areas. Finally, the completed components are removed from their supporting substrate. 
         [0030]    Eugene de Juan Jr. 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 for example E. de Juan Jr., et al., “Retinal tacks”, Am J Ophthalmol. 1985 Mar. 15; 99 (3):272-4. 
         [0031]    Hansjoerg Beutel et al. at the Fraunhofer Institute for Biomedical Engineering IBMT demonstrated the bonding of a gold ball by force, temperature, and ultrasound onto an aluminum metal layer. See for example Hansjoerg Beutel, Thomas Stieglitz, Joerg-Uwe Meyer: “Versatile Microflex-Based Interconnection Technique,” Proc. SPIE Conf. on Smart Electronics and MEMS, San Diego, Calif., March 1998, vol. 3328, pp 174-182. A robust bond can be achieved in this way. However, encapsulation proves difficult to effectively implement with this method. Gold, while biocompatible, is not completely stable under the conditions present in an implant device since it dissolves by electromigration when implanted in living tissue and subject to an electric current. See for example Marcel Pourbaix: “Atlas of Electrochemical Equilibria in Aqueous Solutions”, National Association of Corrosion Engineers, Houston, 1974, pp 399-405. 
         [0032]    A system for retinal stimulation comprising a polyimide-based electrodes being coated with platinum black are described by Andreas Schneider and Thomas Stieglitz. See for example Andreas Schneider, Thomas Stieglitz: “Implantable Flexible Electrodes for Functional Electrical Stimulation”, Medical Device Technology, 2004. 
         [0033]    It is known that circadian rhythms drive our body&#39;s natural cycles of wake and sleep. The hormone melatonin is produced in increasing quantities in the evening and lesser quantities in the morning. Blind people generally do not have normal circadian rhythms and do not produced extra melatonin in the evening. Hence, the perception of light, at least in part, drives the circadian rhythm and the production of melatonin. 
       SUMMARY OF THE INVENTION 
       [0034]    Present invention is a method of improving circadian rhythms in blind people by stimulation the visual neural system. Ideally a retinal prosthesis of the type used to restore vision can be used to restore normal circadian rhythms. Additionally, brightness on the prosthesis can be increased in the morning and decreased in the evening to stimulate normal circadian rhythms. Alternatively, if a retinal prosthesis is not preferable, the retinal can be stimulated externally, during the day and not at night. While such eternal stimulation can not produced artificial vision, it can stimulate normal circadian rhythms. 
         [0035]    One aspect of the present invention is a visual prosthesis for stimulating circadian rhythms comprising at least one electrode suitable for electrically stimulating visual neurons; [0034] an electrical driver for applying a controlled electrical potential on the electrode; and [0035] a timer for controlling activation of the electrical driver. 
         [0036]    Another aspect of the present invention is a flexible circuit electrode array for improving circadian rhythms, comprising [0037] an insulating polymer layer; [0038] at least one trace containing a base coating layer, a conducting layer and a top coating layer, embedded in the insulating polymer layer; and [0039] at least one electrode connected to the conducting layer of the trace through a via in the insulating polymer layer and the top coating layer. 
         [0037]    Anther aspect of the invention is a method of using a flexible circuit electrode array for manufacturing a visual prosthesis for increasing the melatonin levels at night. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0038]      FIG. 1  depicts a perspective view of the implanted portion of the preferred retinal prosthesis including a twist in the array to reduce the width of a scleratomy and a sleeve to promote sealing of the scleratomy. 
           [0039]      FIG. 2  depicts a perspective view of the implanted portion of the retinal prosthesis showing the fan tail in more detail. 
           [0040]      FIGS. 3   a - 3   e  depicts a perspective view of molds for forming the flexible circuit array in a curve. 
           [0041]      FIG. 4  depicts a perspective view of the invention with ribs to help maintain curvature and prevent retinal damage. 
           [0042]      FIG. 5  depicts a top view of a body comprising a flexible circuit electrode array, a flexible circuit cable and a bond pad before it is folded and attached to the implanted portion. 
           [0043]      FIG. 6  depicts a top view of a body comprising a flexible circuit electrode array, a flexible circuit cable and a bond pad after it is folded. 
           [0044]      FIG. 7  depicts a top view of a body comprising a flexible circuit electrode array, a flexible circuit cable and a bond pad after it is folded with a protective skirt. 
           [0045]      FIG. 8  depicts a cross-sectional view of a flexible circuit array with a protective skirt bonded to the back side of the flexible circuit array. 
           [0046]      FIG. 9  depicts a cross-sectional view of a flexible circuit array with a protective skirt bonded to the front side of the flexible circuit array. 
           [0047]      FIG. 10  depicts a cross-sectional view of a flexible circuit array with a protective skirt bonded to the back side of the flexible circuit array and molded around the edges of the flexible circuit array. 
           [0048]      FIG. 11  depicts a cross-sectional view of a flexible circuit array with a protective skirt bonded to the back side of the flexible circuit array and molded around the edges of the flexible circuit array and flush with the front side of the array. 
           [0049]      FIG. 12  depicts a top view of the flexible circuit electrode array. 
           [0050]      FIG. 13  depicts a perspective view of a part of the flexible circuit electrode array. 
           [0051]      FIG. 14  is a graph of experimental data showing patient PB preoperative. 
           [0052]      FIG. 15  is a graph of experimental data showing patient PB postoperative. 
           [0053]      FIG. 16  is a graph of experimental data showing patient TB preoperative. 
           [0054]      FIG. 17  is a graph of experimental data showing patient TB postoperative. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0055]      FIG. 1  shows a perspective view of the implanted portion of the preferred retinal prosthesis. A flexible circuit electrode array  10  is mounted by a retinal tack or similar means to the epiretinal surface. The flexible circuit electrode array  10  is electrically coupled by a flexible circuit cable  12 , which pierces the sclera and is electrically coupled to an electronics package  14 , external to the sclera. 
         [0056]    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  16 . 
         [0057]    The implanted portion of the retinal prosthesis may include 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 (scleratomy). The twist  48  may be a simple sharp twist, or fold; or it may be a longer twist, forming a tube. While the tube is rounder, it reduces the flexibility of the flexible circuit cable  12 . A simple fold reduces the width of the flexible circuit cable  12  with only minimal impact on flexibility. 
         [0058]    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 scleratomy. 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  50  of polyester, collagen, silicone, Gore-Tex.R™. 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. 
         [0059]    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. By placing the device under the rectus muscles with the electronics package  14  in an area of fatty tissue between the rectus muscles, eye motion does not cause any flexing which might fatigue, and eventually damage, the device. 
         [0060]    Human vision provides a field of view that is wider than it is high. This is partially due to fact that we have two eyes, but even a single eye provides a field of view that is approximately 90.degree. high and 140.degree. to 160.degree. degrees wide. It is therefore, advantageous to provide a flexible circuit electrode array  10  that is wider than it is tall. This is equally applicable to a cortical visual array. In which case, the wider dimension is not horizontal on the visual cortex, but corresponds to horizontal in the visual scene. 
         [0061]      FIG. 2  shows a side view of the implanted portion of the retinal prosthesis, in particular, emphasizing the fan tail  24 . When implanting the retinal prosthesis, it is necessary to pass the strap  22  under the eye muscles to surround the sclera. The secondary inductive coil  16  and molded body  18  must also follow the strap  22  under the lateral rectus muscle on the side of the sclera. The implanted portion of the retinal prosthesis is very delicate. It is easy to tear the molded body  18  or break wires in the secondary inductive coil  16 . In order to allow the molded body  18  to slide smoothly under the lateral rectus muscle, the molded body  18  is shaped in the form of a fan tail  24  on the end opposite the electronics package  14 . 
         [0062]    The flexible circuit electrode array  10  is a made by the following process. First, a layer of polymer is applied to a supporting substrate (not part of the array) such as glass. The polymer layer or films of the present invention can be made, for example, any one of the various polyfluorocarbons, polyethylene, polypropylene, polyimide, polyamide, silicone or other biologically inert organic polymers. 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 photoresist 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. 
         [0063]    It is advantageous to make the 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 flexible circuit electrode array  10  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. 
         [0064]    The pressure applied against the retina by the flexible circuit electrode array  10  is critical. Too little pressure causes increased electrical resistance between the array and retina. Common flexible circuit fabrication techniques such as photolithography generally require that a flexible circuit electrode array  10  be made flat. Since the retina is spherical, a flat array will necessarily apply more pressure near its edges, than at its center. With most polymers, it is possible to curve them when heated in a mold. By applying the right amount of heat to a completed array, a curve can be induced that matches the curve of the retina. To minimize warping, it is often advantageous to repeatedly heat the flexible circuit in multiple molds, each with a decreasing radius.  FIG. 3  illustrates a series of molds according to the preferred embodiment. Since the flexible circuit will maintain a constant length, the curvature  30  must be slowly increased along that length. As the curvature  30  decreases in successive molds ( FIGS. 3   a - 3   e ) the straight line length between ends  32  and  34 , must decrease to keep the length along the curvature  30  constant, where mold  3 E approximates the curvature  30  of the retina or other desired neural tissue. The molds provide a further opening  36  for the flexible circuit cable  12  of the array to exit the mold without excessive curvature. 
         [0065]    It should be noted that suitable polymers include thermoplastic materials and thermoset materials. While a thermoplastic material will provide some stretch when heated a thermoset material will not. The successive molds are, therefore, advantageous only with a thermoplastic material. A thermoset material works as well in a single mold as it will with successive smaller molds. It should be noted that, particularly with a thermoset material, excessive curvature  30  in three dimensions will cause the polymer material to wrinkle at the edges. This can cause damage to both the array and the retina. Hence, the amount of curvature  30  is a compromise between the desired curvature, array surface area, and the properties of the material. 
         [0066]    Referring to  FIG. 4 , the edges of the polymer layers are often sharp. There is a risk that the sharp edges of a flexible circuit will cut into delicate retinal tissue. It is advantageous to add a soft material, such as silicone, to the edges of a flexible circuit electrode array  10  to round the edges and protect the retina. Silicone around the entire edge may make the flexible circuit less flexible. It is advantageous to provide silicone bumpers or ribs to hold the edge of the flexible circuit electrode array  10  away from the retinal tissue. Curvature fits against the retina. The leading edge  44  is most likely to cause damage and is therefore fit with molded silicone bumper. Also, edge  46 , where the array lifts off the retina can cause damage and should be fit with a bumper. Any space along the side edges of curvature may cause damage and may be fit with bumpers as well. It is also possible for the flexible circuit cable  12  of the electrode array to contact the retina. It is, therefore, advantageous to add periodic bumpers along the cable  12 . 
         [0067]    It is also advantageous to create a reverse curve or service loop in the flexible circuit cable  12  of the flexible circuit electrode array  10  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 scleratomy. It is not necessary to heat curve the service loop as described above, the flexible circuit electrode array  10  can simply be bent or creased upon implantation. 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. 
         [0068]    With existing technology, it is necessary to place the implanted control electronics outside of the sclera, while a retinal flexible circuit electrode array  10  must be inside the sclera in order to contact the retina. The sclera must be cut through at the pars plana, forming a scleratomy, and the flexible circuit passed through the scleratomy. A flexible circuit is thin but wide. The more electrode wires, the wider the flexible circuit must be. It is difficult to seal a scleratomy over a flexible circuit wide enough to support enough wires for a high resolution array. 
         [0069]      FIG. 5  shows a body  1  containing the flexible circuit electrode array  10 , the flexible circuit cable  12  and the interconnection pad  52  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, an attachment point  54  is provided near the flexible circuit electrode array  10 . A retina tack (not shown) is placed through the attachment point  54  to hold the flexible circuit electrode array  10  to the retina. A stress relief  55  is provided surrounding the attachment point  54 . The stress relief  55  may be made of a softer polymer than the flexible circuit, or it may include cutouts or thinning of the polymer to reduce the stress transmitted from the retina tack to 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 scleratomy. 
         [0070]      FIG. 6  shows the flexible circuit electrode array  10  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 interconnection 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. 
         [0071]    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. 
         [0072]    Further it is advantageous to provide a suture tab  56  in the flexible circuit body near the electronics package  14  to prevent any movement in the electronics package  14  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. 
         [0073]    An alternative to the bumpers described in  FIG. 4 , is a skirt of silicone or other pliable material as shown in  FIGS. 5 to 7 . A skirt  60  covers the flexible circuit electrode array  10 , and extends beyond its edges. It is further advantageous to include windows  62  adjacent to the attachment point  54  to spread any stress of attachment over a larger area of the retina. There are several ways of forming and bonding the skirt  60 . The skirt  60  may be directly bonded through surface activation or indirectly bonded using an adhesive as shown in  FIG. 7 . 
         [0074]    Alternatively, a flexible circuit electrode array  10  may be layered using different polymers for each layer. Using too soft of a polymer may allow too much stretch and break the metal traces. Too hard of a polymer may cause damage to delicate neural tissue. Hence a relatively hard polymer, such a polyimide may be used for the bottom layer and a relatively softer polymer such a silicone may be used for the top layer including an integral skirt to protect delicate neural tissue. 
         [0075]    The simplest solution is to bond the skirt  60  to the back side away from the retina of the flexible circuit electrode array  10  as shown in  FIG. 8 . While this is the simplest mechanical solution, sharp edges of the flexible circuit electrode array  10  may contact the delicate retina tissue. Bonding the skirt to the front side toward the retina of the flexible circuit electrode array  10 , as shown in  FIG. 9 , will protect the retina from sharp edges of the flexible circuit electrode array  10 . However, a window  62  must be cut in the skirt  60  around the electrodes. Further, it is more difficult to reliably bond the skirt  60  to the flexible circuit electrode array  10  with such a small contact area. This method also creates a space between the electrodes and the retina which will reduce efficiency and broaden the electrical field distribution of each electrode. Broadening the electric field distribution will limit the possible resolution of the flexible circuit electrode array  10 . 
         [0076]      FIG. 8  shows another structure where the skirt  60  is bonded to the back side of the flexible circuit electrode array  10 , but curves around any sharp edges of the flexible circuit electrode array  10  to protect the retina. This gives a strong bond and protects the flexible circuit electrode array  10  edges. Because it is bonded to the back side and molded around the edges, rather than bonded to the front side, of the flexible circuit electrode array  10 , the portion extending beyond the front side of the flexible circuit electrode array  10  can be much smaller. This limits any additional spacing between the electrodes and the retinal tissue. 
         [0077]      FIG. 9 , shows a flexible circuit electrode array  10  similar to  FIG. 10 , with the skirt  60 , flush with the front side of the flexible circuit electrode array  10  rather than extending beyond the front side. While this is more difficult to manufacture, it does not lift the electrodes off the retinal surface as with the array in  FIG. 10 . It should be noted that  FIGS. 8 ,  10 , and  11  show skirt  60  material along the back of the flexible circuit electrode array  10  that is not necessary other than for bonding purposes. If there is sufficient bond with the flexible circuit electrode array  10 , it may be advantageous to thin or remove portions of the skirt  60  material for weight reduction. 
         [0078]    The electrode of the present invention preferably contains platinum. Platinum can be present in any form in the electrode. The electrode has preferably increased surface area for greater ability to transfer charge and also having sufficient physical and structural strength to withstand physical stress encountered in its intended use. The electrode contains platinum having a fractal configuration so called platinum gray with an increase in surface area of at least  5  times when compared to shiny platinum of the same geometry and also having improved resistance to physical stress when compared to platinum black. Platinum gray is described in US 2003/0192784 “Platinum Electrode and Method for Manufacturing the Same” to David Zhou, the disclosure of which is incorporated herein by reference. The electrodes of the preferred embodiment are too small to display a color without significant magnification. The process of electroplating the surface coating of platinum gray comprising plating at a moderate rate, i.e., at a rate that is faster than the rate necessary to produce shiny platinum and that is less than the rate necessary to produce platinum black. 
         [0079]    The flexible circuit electrode array  10  is manufactured in layers. A base layer of polymer is laid down, commonly by some form of chemical vapor deposition, spinning, meniscus coating or casting on a supporting rigid substrate like glass. A layer of metal (preferably platinum), preferably sandwich by layers of another metal for example titanium, is applied to the polymer base layer and patterned to create electrodes and traces for those electrodes. Patterning is commonly done by photolithographic methods. The electrodes may be built up by electroplating or similar method to increase the surface area of the electrode and to allow for some reduction in the electrode over time. Similar plating may also be applied to the bond pads. See  FIGS. 5 to 7 . A top polymer layer is applied over the metal layer and patterned to leave openings for the electrodes, or openings are created later by means such as laser ablation. It is advantageous to allow an overlap of the top polymer layer over the electrodes to promote better adhesion between the layers, and to avoid increased electrode reduction along their edges. Alternatively, multiple alternating layers of metal and polymer may be applied to obtain more metal traces within a given width. 
         [0080]      FIG. 12  shows an enlarged top view of the flexible circuit electrode array  10  which is a part of the body  1  as shown for example in  FIG. 5 . The preferred positions of the electrodes  78  and the preferred wiring by the trace metal  79  both embedded in the polymer  71  are shown in the  FIG. 12 . 
         [0081]      FIG. 13  shows a three dimensional view of a part of the flexible circuit electrode array  10 . It shows one electrode  78  which has a contact with the trace metal  79 . It also shows that the trace metal  79  overlaps the electrode  78  and the electrode  78  overlaps the via in the polymer  71 . The  FIG. 13  further shows the adhesion of the polymer  71  with the trace metal  79  and the electrode  78  which results in a very high effective insulation of the trace metal  79  and the electrode  78 .  FIG. 13  shows also that the trace metal  79  is preferably composed of platinum conducting trace  73  covered on the lower and upper side preferably with a thin titanium layer  72   a  and  72   b .  FIG. 13  finally shows that the first applied base polymer  71   a  and the subsequently applied top polymer layer  71   b  form a single polymer layer  71 . 
         [0082]      FIG. 14  shows melatonin levels for a first patient, PB, preoperative. The vertical axis is melatonin levels as measured with a mouth swab every four hours. The horizontal axis is time, where the shaded portions are normal night time hours, over a four day period. There is no significant increase in melatonin levels at night. In fact melatonin decreased on average during the night time periods. 
         [0083]      FIG. 15  shows the same patient, as in  FIG. 14 , using the retinal prosthesis of the current invention. Melatonin levels increased, on average, during the night time hours. 
         [0084]      FIG. 16  shows a second patient TB, preoperative with, on average increased melatonin levels at night, but inconsistent results. 
         [0085]      FIG. 17  shows the second patent, as in  FIG. 16 , using the retinal prosthesis of the current invention. Melatonin level increase significantly, and consistently. 
         [0086]    An alternative embodiment of the present invention can be used when surgery is not desired due to health or surgical apprehension. An external electrode can be attached to the cornea in a form similar to a contact lens, or mounted to the inside of a pair of dark glasses. While such external electrodes can not created formed vision, they can create artificial light during the daytime and be turned, or removed, to create artificial darkness at night. Such an electrode would make it possible to control and improve the melatonin production for patients who are not necessarily vision impaired or blind. 
         [0087]    The present invention will be further illustrated by the following examples, but it is to be understood that the invention is not meant to be limited to the details described herein. 
       EXAMPLES 
       [0088]    In the present example the inventors modulate the above system artificially through retinal prostheses in two patients with retinitis pigmentosa. 
         [0089]    Two patients TB and PB who had retinitis pigmentosa and no light perception (NLP) for five (5) and twenty (20) years were examined. The two patients and a normal control had a multiple saliva samples taken over the course of four (4) days and assayed for melatonin. The two patients then had surgical implantation of the retinal prosthetic implant. The prosthesis was electrically stimulated in one subject. The patients and the normal control were then evaluated with several saliva sampling over the course of four (4) days. 
         [0090]    Melatonin concentrations in saliva samples were measured using a commercially availably melatonin ELISA assay (n=83) from ALPCO Diagnostic, Windham, N.H. 03087. Concentrations were calculated by fitting to a standard logistic equation. A cosinor analysis was performed on the data set using commercially available software from Expert Soft Tech. 
         [0091]    The normal control showed typical circadian levels of melatonin with morning peaks and day time lows with a period of 1430 minutes ( 24  hours=1440 minutes) an about 62% rhythm. 
         [0092]    Both patients with advanced retinitis pigmentosa showed decreased periodicity of melatonin levels preoperatively. Patient PB exhibited a period of 925 minutes with 21% rhythm. While the period could not be calculated for patient TB, he displayed 39% rhythm. 
         [0093]    Patient PB did not show preoperative significant increase in melatonin levels at night. In fact melatonin decreased on average during the night time periods as shown in the shaded normal night time hours over four day period in  FIG. 14 . 
         [0094]    Patient TB showed preoperative on average increased melatonin levels at night, but inconsistent results as shown in the shaded normal night time hours over four day period in  FIG. 16 . 
         [0095]    After surgical implantation of the retinal prosthetic, both patients PB and TB with or without prosthetic stimulation showed doubling of the percent rhythm and a normalization of their periods 1360 and 1430 minutes as would be expected from a normal circadian rhythm. 
         [0096]    Patient PB after using the retinal prosthesis of the current invention showed significant increase in melatonin levels at night as shown in the shaded normal night time hours over four day period in  FIG. 15 . 
         [0097]    Patient TB showed after using the retinal prosthesis of the current invention a significant consistent increase in melatonin levels at night as shown in the shaded normal night time hours over four day period in  FIG. 17 . 
         [0098]    The data suggest that entrainment of circadian rhythms is possible in patients with retinitis pigmentosa, and that the retinohypothalamic pathway that modulates circadian rhythms is intact. 
         [0099]    The data additionally suggest that it is possible to recover entrainment of the circadian rhythm with implantation surgery. 
         [0100]    Accordingly, an improved method making a visual prosthesis and improved method of stimulating neural tissue has been shown. 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.