Electrode array for even neural pressure

<u>Field of the Invention</u>

0001The present invention is generally directed to neural stimulation and more specifically to an improved electrode array and means of attachment for a neural stimulation electrode array. The present invention is more specifically directed to a method of obtaining even pressure between an electrode array and a retina by attaching the electrode array at multiple points.

<u>Background of the Invention</u>

0002In 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.

0003In the early 1930'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.

0004As 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 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.

0005Neural 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.

0006Based 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.

0007One 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.

0008In <patcit id="pcit0001" dnum="US4573481A"><text>1986, Bullara (US Pat. No. 4,573,481</text></patcit>) 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.

0009Dawson and Radtke stimulated cat'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 <patcit id="pcit0002" dnum="US4628933A"><text>US Pat. No. 4,628,933 to Michelson</text></patcit>).

0010The Michelson '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. <patcit id="pcit0003" dnum="US4837049A"><text>US Patent 4,837,049 to Byers </text></patcit>describes spike electrodes for neural stimulation. Each spike electrode pierces neural tissue for better electrical contact. <patcit id="pcit0004" dnum="US5215088A"><text>US Patent 5,215,088 to Norman </text></patcit>describes an array of spike electrodes for cortical stimulation. Each spike pierces cortical tissue for better electrical contact.

0011The 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., <nplcit id="ncit0001" npl-type="s"><text>E. de Juan, et al., 99 Am. J. Ophthalmol. 272 (1985</text></nplcit>). 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. <patcit id="pcit0005" dnum="US5109844A"><text>US Patent 5,109,844 to de Juan</text></patcit> describes a flat electrode array placed against the retina for visual stimulation. <patcit id="pcit0006" dnum="US5935155A"><text>US Patent 5,935,155 to Humayun </text></patcit>describes a retinal prosthesis for use with the flat retinal array described in de Juan.

0012In <patcit id="pcit0007" dnum="US6743345B"><text>U.S. Pat. No. 6,743,345</text></patcit> "Method of Metallizing a Substrate" to Christian Belouet et al. a process for metallizing a substrate is disclosed, comprising coating the part with a precursor composite material layer consisting of a polymer matrix doped with photoreducer material dielectric particles; irradiating the surface of the substrate with a light beam emitted by a laser; and immersing the irradiated part in an autocatalytic bath containing metal ions, with deposition of the metal ions in a layer on the irradiated surface, and wherein the dimension of the dielectric particles is less than or equal to 0.5 µm. The process includes three steps. The first step is to coat the substrate part with a precursor composite material layer consisting of a polymer matrix doped with photoreducer material dielectric particles. The second step is to irradiate the surface of the substrate with a light beam emitted by a laser. The third step is to immerse the irradiated part in an autocatalytic bath containing metal ions, with deposition of the metal ions in a layer on the irradiated surface, wherein the dimension of the dielectric particles is less than or equal to 0.5 µm.

0013In <patcit id="pcit0008" dnum="US5599592A"><text>U.S. Pat. No. 5,599,592</text></patcit> "Process for the Metallization of Polymer Materials and Products Thereto Obtained" to Lucien D. Laude a positive metallization process for metallizing a polymer composite piece containing a polymer material and oxide particles is disclosed, the oxide particles being made of one or more oxides, comprising three successive steps. The first step consists of the irradiation of a surface area of a polymer piece to be metallized with a light beam emitted by an excimer laser. The polymer piece is made from a polymer material and oxide particles. The oxide particles are made from one or more oxides. The second step consists of immersing the irradiated polymer piece in at least one autocatalytic bath containing metal ions. The immersion induces the deposit of the metal ions onto the irradiated surface area to form a metal film on the surface area, resulting in the selective metallization of the surface area of the polymer piece. The third step consists of thermally processing the metallized polymer piece to induce diffusion of the deposited metal film into the polymer material of the polymer piece. The disclosure of <patcit id="pcit0009" dnum="US5599592A"><text>U.S. Pat. No. 5,599,592</text></patcit> is incorporated herein by reference.

0014Lucien D. Laude et al. report that excimer lasers are effective tools in engraving ceramics and polymers, changing irreversibly the surface of the irradiated material, and restricting these effects to specific areas of interest. See <nplcit id="ncit0002" npl-type="s"><text>L. D. Laude, K Kolev, CI. Dicara and C. Dupas-Bruzek "Laser Metallization for Microelectronics for Bio-applications", Proc. of SPIE Vol. 4977 (2003), pp 578-586</text></nplcit>.

0015In <patcit id="pcit0010" dnum="US5935155A"><text>U.S. Pat. No. 5,935,155</text></patcit> "Visual Prosthesis and Method of Using Same" to Mark S. Humayan et al. it is disclosed a visual prosthesis, comprising means for perceiving a visual image, said means producing a visual signal output in response thereto; retinal tissue stimulation means adapted to be operatively attached to a retina of a user; and wireless visual signal communication means for transmitting said visual signal output to said retinal tissue stimulation means.

0016In <patcit id="pcit0011" dnum="US6878643B"><text>U.S. Pat. No. 6,878,643</text></patcit> "Electronic Unit integrated Into a Flexible Polymer Body" to Peter a. Krulevitch et al. it is disclosed a method of fabricating an electronic apparatus, comprising the steps of providing a silicone layer on a matrix, providing a metal layer on said silicone layer, providing a second layer of silicone on said silicone layer, providing at least one electronic unit connected to said metal layer, and removing said electronic apparatus from said matrix wherein said silicone layer and said second layer of a silicone provide a spherical silicone body.

0017J. Delbeke et al. demonstrate that silicone rubber biocompatibility is not altered by the metallization method. See <nplcit id="ncit0003" npl-type="s"><text>V. Cince, M.-A. Thil, C. Veraart, I. M. Colin and J. Delbeke "Biocompatibility of platinum-metallized silicone rubber: in vivo and in vitro evaluation", J. Biomater. Sci. Polymer Edn, Vol. 15, No. 2, pp. 173-188 (2004</text></nplcit>).

0018<patcit id="pcit0012" dnum="WO2006116765A"><text>WO 2006/116765 A</text></patcit> discloses a flexible circuit electrode array in which a curve is induced by applying the right amount of heat to a completed array.

0019All of these soft polymer arrays approximate the shape of neural tissue, particularly the retina. However, there is a need for an improved means for attaching an electrode array to neural tissue and, thereby, improving the array's ability to conform to the neural tissue.

<u>Summary of the Invention</u>

0020An electrode array attached to neural tissue, such as the retina, necessarily has graded pressure exerted on the tissue, with higher pressure near the attachment point. Pressure improves contact between the electrodes and neural tissue while too much pressure may damage neural tissue. Hence it is advantageous to obtain equal pressure across the array field. In the present invention multiple and selective attachment points are provided on an electrode array allowing a surgeon to select the attachment points providing the best electrode tissue contact. The present invention is directed towards an electrode array as set out in claim 1.

<u>Brief Description of the Drawings</u>

0021<ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001"><b>FIG. 1</b></figref> is a perspective view of the preferred electrode array with two attachment points.</li><li><figref idref="f0001"><b>FIG. 2</b></figref> is a perspective view of the preferred electrode array with three attachment points.</li><li><figref idref="f0002"><b>FIG. 3</b></figref> depicts the electrode array of a related example.</li><li><figref idref="f0003"><b>FIG. 4</b></figref> depicts an electrode array of an alternate two point attachment</li><li><figref idref="f0004"><b>FIG. 5</b></figref> depicts an electrode array of an alternate three point attachment.</li><li><figref idref="f0005"><b>FIG. 6</b></figref> depicts an electrode array with another alternate three point attachment.</li><li><figref idref="f0006"><b>FIG. 7</b></figref> shows the whole flexible polymer array with the bond pad and the traces with holes at the edge of the electrode array.</li><li><figref idref="f0007"><b>FIG. 8</b></figref> shows an enlarged view of the electrode array with holes at the edge of the polyimide to improve silicone adhesion.</li><li><figref idref="f0008"><b>FIG. 9</b></figref> depicts the top view of the flexible circuit array being enveloped within an insulating material.</li><li><figref idref="f0008"><b>FIG. 10</b></figref> depicts a cross-sectional view of the flexible circuit array being enveloped within an insulating material.</li><li><figref idref="f0008"><b>FIG. 11</b></figref> depicts a cross-sectional view of the flexible circuit array being enveloped within an insulating material with open electrodes and the material between the electrodes.</li><li><figref idref="f0008"><b>FIG. 12</b></figref> depicts a cross-sectional view of the flexible circuit array being enveloped within an insulating material with open electrodes.</li><li><figref idref="f0008"><b>FIG. 13</b></figref> depicts a cross-sectional view of the flexible circuit array being enveloped within an insulating material with electrodes on the surface of the material.</li><li><figref idref="f0009"><b>FIG. 14</b></figref> depicts a cross-sectional view of the flexible circuit array being enveloped within an insulating material with electrodes on the surface of the material insight the eye with an angle in the fold of the flexible circuit cable and a fold between the circuit electrode array and the flexible circuit cable.</li><li><figref idref="f0009"><b>FIG. 15</b></figref> depicts a side view of the enlarged portion of the flexible circuit array being enveloped within an insulating material with electrodes on the surface of the material in the eye and contacting the retina.</li><li><figref idref="f0010"><b>FIG. 16</b></figref> is a perspective view of the implanted portion of the preferred retinal prosthesis.</li><li><figref idref="f0011"><b>FIG. 17</b></figref> is a side view of the implanted portion of the preferred retinal prosthesis showing the fan tail in more detail.</li><li><figref idref="f0012"><b>FIG. 18</b></figref> is a view of the completed package attached to an electrode array.</li><li><figref idref="f0012"><b>FIG. 19</b></figref> is a cross-section of the package.</li></ul>

<u>Detailed Description of the Preferred Embodiments</u>

0022The 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.

0023<figref idref="f0001"><b>Figure 1</b></figref> shows the preferred electrode array. The array <b>10</b> is preferably made of metal traces sandwiched between polyimide layers. The array <b>10</b> and cable <b>12</b> are a single polyimide structure. A relatively hard polymer, such as polyimide, is needed to protect delicate metal traces from breaking. A molded array body <b>34,</b> preferably silicone, is molded over the polyimide structure. Perforations <b>58</b> in the polyimide promote adhesion of the molded array body <b>34.</b> A backbone structure <b>38</b> is molded in silicone across the back of the array <b>10.</b> Attachment points <b>54</b> are provided on either side of the array field to provide even pressure across the array surface. A strain relief <b>56</b> is provided around each attachment point <b>54.</b> The strain relief <b>56</b> may be thinner or softer polymer. The strain relief <b>56</b> may also include cut out portions. In the preferred embodiment the attachment point <b>54</b> is a hole suitable to accept a retinal tack (not shown).

0024<figref idref="f0001"><b>Figure 2</b></figref> shows an alternate embodiment with three attachment points <b>54.</b> The additional attachment point is in the center of the electrode field. With either embodiment, a surgeon may decide at the time of surgery which attachment point to use. The ideal attachment may be determined through impedance. Electrodes with higher impedance have more intimate contact with neural tissue and result in lower a threshold of neural stimulation. Hence, a surgeon may place a tack in the attachment point <b>54</b> closest to the cable <b>12</b> and measure impedance across the electrode array. If acceptable impedance is found, no additional tacks are required. If not, tacks may be placed where additional force is needed to obtain good electrode contact.

0025A retinal array is pre-curved to match the approximate curvature of the retina. However, retinas vary considerably in their curvature. In a small eye, the array may not be curved enough. Using only the center attachment point <b>54</b> would achieve the best result. In a large eye, the array may be too curved. Using the outer attachment points <b>54</b> would achieve the best result.

0026<figref idref="f0002"><b>Figure 3</b></figref> shows the flexible circuit electrode array <b>10</b> in another related example. A flexible circuit cable <b>12</b> connects to the flexible circuit electrode array <b>10</b>. Further, an attachment point <b>54</b> is provided near the heel of the flexible circuit electrode array <b>10</b>. A retina tack (not shown) is placed through the attachment point <b>54</b> to hold the flexible circuit electrode array <b>10</b> to the retina or other neural tissue. A stress relief <b>56</b> is provided surrounding the attachment point <b>54.</b> The stress relief <b>56</b> 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 <b>10</b>. A molded body <b>34</b> covers the flexible circuit electrode array <b>10</b>, and extends beyond its edges. It may be further advantageous to include wings <b>36</b> adjacent to the attachment point <b>54</b> to spread any stress of attachment over a larger area of the retina or other neural tissue. There are several ways of forming and bonding the molded body <b>34.</b> The molded body <b>34</b> may be directly bonded through surface activation or indirectly bonded using an adhesive. The molded body <b>34</b> may be a molded completely around the electrode array <b>10</b> and cable <b>12.</b>

0027Preferably the electrode array <b>10</b> is constructed from a hard polymer such as polyimide while the molded body <b>34</b> is constructed from a softer polymer such as silicone. Traces and electrodes can be laid out on a hard polymer by photolithography and the hard polymer protects the delicate traces. A soft polymer molded body <b>34</b> then protects the neural tissue from the hard polymer.

0028Further a strap <b>26</b> may be provided over the array <b>10</b> opposite the attachment point <b>54</b> near the heel attached at either end by attachment points <b>54</b> with retinal tacks. Retinal nerve fibers and blood vessels run orbitally out from the optic nerve. It may be advantageous not to tack between the electrode array <b>10</b> and the optic nerve as you may damage the nerve fibers which are stimulated by the electrode array <b>10.</b> The strap <b>26</b> allows the attachment points <b>54</b> to be out of the line of the stimulated nerve fibers. The optic nerve <b>30</b> is the central access point for both nerve fibers and blood vessels. <b>32.</b> A tack through either a nerve fiber or blood vessel may cause damage to the area to be stimulated by the electrode array <b>10.</b>

0029Alternatively, <figref idref="f0003"><b>figure 4</b></figref> show a central secondary attachment point <b>54,</b> with a stress relief <b>56.</b> If the array is not aligned with the nerve fibers a central secondary attachment point may be preferable. <figref idref="f0003">Figure 4</figref> varies from <figref idref="f0001">figure 2</figref> in that the attachment point <b>54</b> near the toe is within the flexible body <b>34</b> but outside the array <b>10.</b> This provides additional stress relief from attachment.

0030<figref idref="f0004"><b>Figure 5</b></figref> shows another related example . It this case the array may be place in the preferred orientation or an opposite orientation, with the cable passing over the optic nerve. The attachment points <b>54</b> includes stress reliefs <b>56.</b> Attachment points <b>54,</b> with stress relief <b>56,</b> are included in the wings <b>62.</b> An additional advantage of this embodiment is that any rotational torque from the array cable is transmitted to the electrode field portion of the flexible body.

0031<figref idref="f0005"><b>Figure</b> 6</figref> shows another related example similar to the embodiment shown in <figref idref="f0002">figure 3</figref>, but with attachment points <b>54</b> integral to the array body rather than on a separate strap. As with the embodiment of <figref idref="f0002">figure 3</figref>, the attachment points are outside of the area of the nerve fibers and blood vessels supplying the areas to be stimulated.

0032<figref idref="f0006"><b>Figure 7</b></figref> shows the preferred electrode array for a visual prosthesis. The structure is a single polyimide sandwich with metal traces. The array <b>10</b> is at one end. Bond pads <b>92</b> are at the other end and the cable <b>12</b> is in the middle. One trace connects each electrode with a bond pad. The flexible circuit <b>1</b> is a made by the following process. First, a layer of polymer (such as polyimide, fluoropolymers, 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.

0033It is advantageous to make this metal thicker at the electrode to improve contact with neural tissue, and at the bond pad to improve contact with the package. 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 <b>14</b> and the electrodes may be accomplished by laser ablation or reactive ion etching (RIE) or photolithography and wet etch. Making the electrode openings in the top layer smaller than the electrodes promotes adhesion by avoiding delamination around the electrode edges.

0034<figref idref="f0007"><b>Figure 8</b></figref> is an enlarged view of the electrode array <b>10.</b> Traces must be routed around the attachment point <b>54</b> and stress relief <b>56.</b> The electrode field 9, shown by a dotted line, is that portion of the electrode array having electrodes and stimulating neural tissue.

0035<figref idref="f0008"><b>Figure 9</b></figref> depicts the top view of the flexible circuit array <b>10</b> being enveloped within a molded body <b>34.</b> The electrode array <b>10</b> is encased within the oval-shaped molded body <b>34,</b> a plurality of electrodes <b>13</b> made of a conductive material, such as platinum or one of its alloys, but that can be made of any conductive biocompatible material such as iridium, iridium oxide or titanium nitride. The electrode array <b>10</b> is enveloped within a molded body <b>34</b> that is preferably silicone. "Oval-shaped" electrode array body means that the body may approximate either a square or a rectangle shape, but where the corners are rounded. This shape of an electrode array is described in the <patcit id="pcit0013" dnum="US20020111658A" dnum-type="L"><text>U.S. Patent Application No. 20020111658</text></patcit>, entitled "Implantable retinal electrode array configuration for minimal retinal damage and method of reducing retinal stress" and No. <patcit id="pcit0014" dnum="US20020188282A"><text>20020188282</text></patcit>, entitled "Implantable drug delivery device" to Robert J. Greenberg et al., the disclosures of both are incorporated herein by reference.

0036The molded body <b>34</b> is made of a soft material that is compatible with the electrode array <b>10.</b> In a preferred embodiment the molded body <b>34</b> made of silicone having hardness of about 50 or less on the Shore A scale as measured with a durometer. In an alternate embodiment the hardness is about 25 or less on the Shore A scale as measured with a durometer.

0037<figref idref="f0008"><b>Figure 10</b></figref> depicts a cross-sectional view of the flexible circuit array <b>10</b> being enveloped within the molded body 34. It shows how the edges of the molded body <b>34</b> are lifted off due to the contracted radius at the edges. The electrode array <b>10</b> preferably also contains a fold A between the cable <b>12</b> and the electrode array <b>10.</b> The angle of the fold A secures a relief of the implanted material.

0038<figref idref="f0008"><b>Figure 11</b></figref> depicts a cross-sectional view of the flexible circuit array <b>10</b> being enveloped within a molded body <b>34</b> with open electrodes <b>13</b> and the molded body <b>34</b> between the electrodes <b>13.</b>

0039<figref idref="f0008"><b>Figure 12</b></figref> depicts a cross-sectional view of the flexible circuit array <b>10</b> being enveloped within the molded body <b>34</b> with open electrodes <b>13.</b> This is another embodiment wherein the electrodes <b>13</b> are not separated by the molded body <b>34.</b> This may allow closer contact with the neural tissue.

0040<figref idref="f0008"><b>Figure 13</b></figref> depicts a cross-sectional view of the flexible circuit array <b>10</b> being enveloped within the molded body <b>34</b> with electrodes <b>13</b> on the surface of the molded body <b>34.</b> This is a further embodiment with the electrode <b>13</b> on the surface of the molded body, preferably silicone. The embodiments shown in

0041<figref idref="f0009"><b>Figure 14</b></figref> depicts a cross-sectional view of the flexible circuit array <b>10</b> being enveloped within the molded body <b>34</b> with electrodes <b>13</b> on the surface of the molded body <b>34</b> insight the eye with an angle K in the fold of the flexible circuit cable <b>12</b> and a fold A between the circuit electrode array <b>10</b> and the flexible circuit cable <b>12.</b> The molded body <b>34</b> and electrode array body <b>10</b> are in intimate contact with retina R. The surface of electrode array body <b>10</b> in contact with retina R is a curved surface with a matched radius compared to the spherical curvature of retina R to minimize pressure concentrations therein. Further, the decreasing radius of spherical curvature of the molded body <b>34</b> near its edge forms edge relief that causes the edges of the molded body <b>34</b> to lift off the surface of retina R eliminating pressure concentrations at the edges. The edge of molded body <b>34</b> is rounded to reduce pressure and cutting of retina R.

0042<figref idref="f0009"><b>Figure 15</b></figref> shows a part of the <figref idref="f0009">Figure 14</figref> enlarged showing the electrode array 10 and the electrodes <b>13</b> enveloped by the molded body <b>34,</b> preferably silicone in intimate contact with the retina R.

0043The electrode array <b>10</b> embedded in or enveloped by the molded body <b>34</b> can be preferably produced through curing the silicone in a mold around the polyimide array <b>10.</b> The molded body <b>34</b> has a shape with a decreasing radius at the edges so that the edges of the molded body <b>34</b> lift off from the retina R.

0044<figref idref="f0010"><b>Figure 16</b></figref> shows a perspective view of the implanted portion of the preferred retinal prosthesis. A flexible circuit <b>1</b> includes a flexible circuit electrode array <b>10</b> which is mounted by a retinal tack (not shown) or similar means to the epiretinal surface. The flexible circuit electrode array <b>10</b> is electrically coupled by a flexible circuit cable <b>12,</b> which pierces the sclera and is electrically coupled to an electronics package <b>14,</b> external to the sclera.

0045The electronics package <b>14</b> is electrically coupled to a secondary inductive coil <b>16.</b> Preferably the secondary inductive coil <b>16</b> is made from wound wire. Alternatively, the secondary inductive coil <b>16</b> may be made from a flexible circuit polymer sandwich with wire traces deposited between layers of flexible circuit polymer. The secondary inductive coil receives power and data from a primary inductive coil <b>17,</b> which is external to the body. The electronics package <b>14</b> and secondary inductive coil <b>16</b> are held together by the molded body <b>18.</b> The molded body <b>18</b> holds the electronics package <b>14</b> and secondary inductive coil <b>16</b> end to end. The secondary inductive coil <b>16</b> is placed around the electronics package <b>14</b> in the molded body <b>18.</b> The molded body <b>18</b> holds the secondary inductive coil <b>16</b> and electronics package <b>14</b> in the end to end orientation and minimizes the thickness or height above the sclera of the entire device. The molded body <b>18</b> may also include suture tabs <b>20.</b> The molded body <b>18</b> narrows to form a strap <b>22</b> which surrounds the sclera and holds the molded body <b>18,</b> secondary inductive coil <b>16,</b> and electronics package <b>14</b> in place. The molded body <b>18,</b> suture tabs <b>20</b> and strap <b>22</b> 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 <b>16</b> and molded body <b>18</b> are preferably oval shaped. A strap <b>22</b> can better support an oval shaped coil. It should be noted that the entire implant is attached to and supported by the sclera. An eye moves constantly. The eye moves to scan a scene and also has a jitter motion to improve acuity. Even though such motion is useless in the blind, it often continues long after a person has lost their sight. By placing the device under the rectus muscles with the electronics package 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.

0046<figref idref="f0011"><b>Figure 17</b></figref> shows a side view of the implanted portion of the retinal prosthesis, in particular, emphasizing the fan tail <b>24.</b> When implanting the retinal prosthesis, it is necessary to pass the strap <b>22</b> under the eye muscles to surround the sclera. The secondary inductive coil <b>16</b> and molded body <b>18</b> must also follow the strap <b>22</b> 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 <b>18</b> or break wires in the secondary inductive coil <b>16.</b> In order to allow the molded body <b>18</b> to slide smoothly under the lateral rectus muscle, the molded body <b>18</b> is shaped in the form of a fan tail <b>24</b> on the end opposite the electronics package <b>14.</b> The strap <b>22</b> further includes a hook <b>28</b> the aids the surgeon in passing the strap under the rectus muscles.

0047Referring to <figref idref="f0012"><b>figure 18</b></figref><b>,</b> the flexible circuit <b>1,</b> includes platinum conductors <b>94</b> insulated from each other and the external environment by a biocompatible dielectric polymer <b>96,</b> preferably polyimide. One end of the array contains exposed electrode sites that are placed in close proximity to the retinal surface <b>10.</b> The other end contains bond pads <b>92</b> that permit electrical connection to the electronics package <b>14.</b> The electronic package <b>14</b> is attached to the flexible circuit <b>1</b> using a flip-chip bumping process, and epoxy underfilled. In the flip-chip bumping process, bumps containing conductive adhesive placed on bond pads <b>92</b> and bumps containing conductive adhesive placed on the electronic package <b>14</b> are aligned and melted to build a conductive connection between the bond pads <b>92</b> and the electronic package <b>14.</b> Leads <b>76</b> for the secondary inductive coil <b>16</b> are attached to gold pads <b>78</b> on the ceramic substrate <b>60</b> using thermal compression bonding, and are then covered in epoxy. The electrode array cable <b>12</b> is laser welded to the assembly junction and underfilled with epoxy. The junction of the secondary inductive coil <b>16,</b> array <b>1,</b> and electronic package <b>14</b> are encapsulated with a silicone overmold <b>90</b> that connects them together mechanically. When assembled, the hermetic electronics package <b>14</b> sits about 3mm away from the end of the secondary inductive coil.

0048Since the implant device is implanted just under the conjunctiva it is possible to irritate or even erode through the conjunctiva. Eroding through the conjunctiva leaves the body open to infection. We can do several things to lessen the likelihood of conjunctiva irritation or erosion. First, it is important to keep the over all thickness of the implant to a minimum. Even though it is advantageous to mount both the electronics package <b>14</b> and the secondary inductive coil <b>16</b> on the lateral side of the sclera, the electronics package <b>14</b> is mounted higher than, but not covering, the secondary inductive coil <b>16.</b> In other words the thickness of the secondary inductive coil <b>16</b> and electronics package should not be cumulative.

0049It is also advantageous to place protective material between the implant device and the conjunctiva. This is particularly important at the scleratomy, where the thin film electrode array cable <b>12</b> penetrates the sclera. The thin film electrode array cable <b>12</b> must penetrate the sclera through the pars plana, not the retina. The scleratomy is, therefore, the point where the device comes closest to the conjunctiva. The protective material can be provided as a flap attached to the implant device or a separate piece placed by the surgeon at the time of implantation. Further material over the scleratomy will promote healing and sealing of the scleratomy. Suitable materials include <u>DACRON®, TEFLON®, GORETEX® (ePTFE), TUTOPLAST®</u> (sterilized sclera), <u>MERSILENE®</u> (polyester) or silicone.

0050Referring to <figref idref="f0012"><b>figure 19</b></figref><b>,</b> the package <b>14</b> contains a ceramic substrate <b>60,</b> with metalized vias <b>65</b> and thin-film metallization <b>66.</b> The package <b>14</b> contains a metal case wall <b>62</b> which is connected to the ceramic substrate <b>60</b> by braze joint <b>61.</b> On the ceramic substrate <b>60</b> an underfill <b>69</b> is applied. On the underfill <b>69</b> an integrated circuit chip <b>64</b> is positioned. On the integrated circuit chip <b>64</b> a ceramic hybrid substrate <b>68</b> is positioned. On the ceramic hybrid substrate <b>68</b> passives <b>70</b> are placed. Wirebonds <b>67</b> are leading from the ceramic substrate <b>60</b> to the ceramic hybrid substrate <b>68.</b> A metal lid <b>84</b> is connected to the metal case wall <b>62</b> by laser welded joint <b>63</b> whereby the package <b>14</b> is sealed.

0051Accordingly, 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 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.