Abstract:
A retina implant including a chip adapted to be implanted into the interior of eye in subretinal contact with the retina. The chip has a plurality of pixel elements on a side thereof facing the lens for receiving an image projected into the retina and a plurality of electrodes for stimulating retina cells. The implants further includes a receiver coil for inductively coupling thereinto electromagnetic energy. The receiver coil coupled to a means for converting an alternating voltage induced into the receiver coil in a direct voltage suited for supplying the chip. The receiver coil is configured as a component separate from the chip, and for being positioned on the eye ball outside the sclera. The chip is connected to the receiver coil via a connecting lead which, in the implanted condition interconnects the interior and the exterior of the eye ball.

Description:
RELATED APPLICATIONS 
   This application is a continuation-in-part of the PCT application PCT/EP00/03962 filed 3 May 2000 entitled “A RETINA IMPLANT AND A METHOD FOR MANUFACTURING SAME” and claims the benefits of the German Applications 199 21 398.4 filed 7 May 1999, and 199 31 083.1 filed 6 Jul. 1999. 

   FIELD OF THE INVENTION 
   The invention relates to a retina implant having a chip for subretinal implantation, and comprising a receiver coil for inductively coupling thereinto electromagnetic energy, the coil being connected to means for converting an alternating voltage induced into the receiver coil into a direct voltage suited for supplying the chip. 
   The invention, further, is related to a method for manufacturing a retina implant as specified before. 
   Implants of that kind are generally known. 
   BACKGROUND OF THE INVENTION 
   Recently, retina implants have been developed that are intended to be used for the treatment of patients whose viewing ability has gone lost entirely or in part due to retinal defects. As a matter of principle, a light-sensitive chip shall be implanted into the subretinal space below the retina. The chip is provided with a plurality of pixel elements receiving an image projected on the retina through the still intact lens of the eye, for converting same into electrical signals and for further converting same into electrical stimuli via a plurality of stimulation electrodes to stimulate the retinal cells adjacent the chip, in order to reconstruct or improve vision of blind or partially blind patients. 
   U.S. Pat. No. 4,628,933 discloses a retina implant which, however, is not intended to be used for subretinal implantation but for epiretinal implantation instead, i.e. the light-sensitive chip shall not be implanted into the subretinal space but directly onto the surface of the retina. The stimulation electrodes, therefore, are not provided on the side of the chip facing the lens but on its rear side instead. 
   It has been found out that for subretinal implants as well as for epiretinal implants it is necessary to feed external energy in order to actively amplify the received light signals and for converting same into stimulation signals for the adjacent cells. 
   For that purpose, U.S. Pat. No. 4,628,933 suggests to transmit energy to the implant via electromagnetic induction. For that purpose, a receiver coil is wound around the periphery of the implant chip. By means of the receiver coil, radiofrequency energy having been transmitted from an external source of energy which, for example, may be located in an eyeglass frame, is received and is transformed into electrical energy for supplying the chip. 
   Considering that such a coil must be provided with a sufficient number of windings, must have a considerable coil diameter for an effective coupling of radiofrequency energy and, further, appropriate installations must be provided for rectifying and smoothening the induced alternating current, a chip of that kind would hardly be adapted to be implanted into the human eye due to its substantial dimensions. 
   For that purpose, subretinal implants have been developed recently which have not been supplied via rf coupling of electromagnetic energy but via invisible infrared radiation which was converted into electrical energy by means of an appropriate photovoltaic layer. 
   A subretinal implant of the type specified before is disclosed e.g. in WO 98/17343. 
   However, it must be considered to be disadvantageous in that case that for operating the implant, infrared radiation must continuously be irradiated into the eye. 
   It is, therefore, an object underlying the invention to provide an improved retina implant being supplied with electromagnetic energy via inductive coupling and which may be implanted into the subretinal space simply and without the risks of complications. 
   Moreover, a method for manufacturing such a retina implant shall be provided. 
   SUMMARY OF THE INVENTION 
   According to a retina implant as specified at the outset, this object is achieved in that the receiver coil is configured to be received and positioned on the eyeball outside the sclera. 
   By doing so, it is possible to utilize a sufficiently dimensioned receiver coil positioned outside the eyeball which can be inserted preferably by means of surgical methods avoiding to guide the implant through the vitreous body of the eye. 
   As the receiver coil is affixed to the sclera outside the eye, the chip that has to be implanted into the subretinal space may be dimensioned appropriately which is of particular advantage for an implantation into the subretinal space. In contrast, the receiver coil may be provided with a sufficiently large cross-section and a sufficiently high number of windings without incurring disadvantageous effects. 
   In a preferred embodiment of the invention, the receiver coil, the chip as well as connecting leads leading to the chip are housed within a flat plastic material body. 
   This enables to utilize a compact design and low-risk implantation techniques by effecting a sclera incision on the lateral portion in the area of the eye equator. The end of the flat plastic material body on which the chip is located, may be brought into the subretinal space via the incision. The operation that may be used insofar is partially similar to the surgical technique described in German disclosure document DE 197 41 487 A1. 
   According to a preferred embodiment of the invention, the converting means is configured as a unit separate from the chip, the unit being adapted to be positioned on the eyeball outside the sclera. 
   By this feature, the portion of the entire retina implant to be implanted into the subretinal space is made still smaller because the converter means must be provided with a rectifier and with smoothing capacitors which require a certain space and, hence, may not be directly combined with the chip without substantially increasing the dimensions thereof. 
   By using such a design, that portion of the implant to be implanted into the subretinal space of the eyeball is made still smaller so that that portion of the plastic material body may be configured as a thin foil and the chip may be integrated into a terminal end thereof. 
   In a preferred embodiment of the invention, the plastic material body comprises an annular portion having a central opening, the annular portion being adjoined by a flat extension. 
   By doing so, the receiver coil may be integrated into the annular portion of the plastic material body in a most suitable manner, whereas the chip may be provided at the end of the flat extension. 
   According to still another preferred embodiment of the invention, the annular portion is dimensioned as to enclose the lateral straight eye muscle rudiment. 
   This measure has the advantage that a particularly preferable arrangement and positioning of the receiver coil on the eye is achieved. For the implantation, the eye muscle must be severed, however, may thereafter be sewed together again which, in view of modern surgical techniques, does not present a problem at all. 
   In such an arrangement, the excitation coils for the energy supply may be arranged in the area of the temples, for example on an eyeglass frame. 
   In contrast, the converting means is comprised within the plastic material body in a position adjacent the receiver coil. 
   By doing so, the converting means which requires a certain space is positioned most advantageously. 
   According to still another embodiment of the invention, the receiver coil comprises windings integrated into the annular portion and being, preferably, configured in a spiralled pattern. 
   By doing so, the receiver coil may advantageously be integrated into the annular portion of the plastic material body. 
   In a supplemental improvement of this embodiment, the annular portion is subdivided into a plurality of sections in a circumferential direction, the sections being separated from each other by gaps and being electrically and mechanically interconnected. 
   This feature allows to improve the flexibility of the annular portion so that the annular portion of the plastic material body may perfectly be applied to the bulged surface of the eye even if it consists of a material of relatively high tensile strength. 
   Insofar, the sections may be interconnected with each other by a fin in a radial direction, or the sections may be made to adhere each other in a spiralled configuration. 
   Preferably, the individual sections each have a plurality of windings and are interconnected in a radial direction via fins which also carry the electrical connections between neighbored windings. 
   By doing so, it is possible to obtain a particularly good flexibility and adaptation to the bulged surface of an eyeball, wherein the annular portion may first be manufactured as a planar body and may subsequently be brought into the desired bulged shape. 
   According to still another modification of the annular portion of the plastic material body, it may have a meander shape in order to obtain an improved flexibility. 
   According to still another embodiment of the invention, strain relief means are provided at least between the converter means and a connection lead leading to the chip or to the receiver coil. 
   The strain relief means may, for example, be obtained by a meander-shaped configuration substantially in the area between the annular portion and the flat extension where the converter means is received or in an area immediately adjacent the converter means. 
   By doing so, the electrical interconnection between the receiver coil, the converter means and the chip are protected against hazardous influences which may result from the continuous movement of the eyeball, so that even years after an implantation a reliable voltage supply for the implanted chips is guaranteed. 
   In a preferred embodiment of the invention, the receiver coil has a number of windings of about between 50 and 200, preferably about 100 windings. 
   With such a winding number, an appropriate energy transmission and a sufficient voltage at the receiver coil may be guaranteed. 
   A receiver coil of that kind may be operated in combination with an external transmitter coil at a frequency of 1 MHz, when the transmitter coil has about 1000 windings with a diameter of about 50 mm and is attached to, for example, an eyeglass frame. 
   In a preferred embodiment of the invention, the receiver coil has an outer diameter of about between 12 and 20 mm and an inner diameter at the opening of about between 8 and 16 mm. 
   With such dimensions, an advantageous adaptation to the anatomy of the human eye may be guaranteed. 
   In still another preferred embodiment of the invention, the flat extension is provided with a plurality of perforations. 
   These perforations, for example, may be arranged along an array of about between 0.1 and 1 mm width and have a diameter in the area of about between 20 and 200 μm. 
   This allows the diffusion of nutrients and oxygen between the pigment epithelium and the retina, so that disadvantages that could be caused by implanting an impermeable item are avoided. 
   According to still another preferred embodiment of the invention, the chip is embedded in the flat extension, the active side of the chip lying open at the surface for stimulating cells. 
   This makes sure that the chip may be advanced in a lateral direction into the subretinal space during an appropriate surgical technique utilizing a sclera incision in the area of the lateral eye muscle. 
   According to still another preferred embodiment of the invention, the flat plastic material body is provided with lugs for affixing the plastic material body to the eyeball. 
   This ensures a safe seating in the desired position on the eyeball. The lugs may either be provided at the annular portion as well as in the flat extension, preferably in the area where the converter means are received. 
   According to another embodiment of the invention, the converter means comprises means for processing an information signal transmitted together with the electromagnetic energy, in particular for processing a referenced signal indicative for ambient light intensity or brightness. 
   This allows an adaptation of the output signal amplitude of the chip under varying ambient light intensity or brightness conditions. By doing so, the performance of the implanted chip may be improved significantly. 
   In a preferred embodiment of the invention, the flat plastic material body is generated on an auxiliary substrate and may be separated therefrom thereafter. 
   By doing so, the manufacturing method is significantly simplified. 
   When doing so, the strip conductors are preferably generated on the surface by means of thin film methods (vapor deposition or sputtering) and are then microstructured photolithographically. 
   By using these well-established manufacturing process, a high precision and quality may be guaranteed. 
   The object underlying the invention is, further, achieved by a method for manufacturing a retina implant having a chip for subretinal implantation, and comprising a receiver coil for inductively coupling thereinto electromagnetic energy, means for converting an alternating voltage induced into the receiver coil into a direct voltage suited for supplying the chip, the method comprising the steps of:
         manufacturing a flat plastic material body having an annular portion with a central opening, the annular portion being adjoined by a flat extension,   depositing metallic strip conductors on a surface of the annular portion in a spiralled configuration for making windings of the receiver coil and for creating connecting leads between the receiver coil, the converter means and the chip,   affixing the chip and the converter means to the plastic material body,   depositing an isolation layer over the metallic strip conductors.       

   According to the invention, one can manufacture a retina implant accordingly, having a thin foil-type extension with the chip to be implanted, the retina implant being configured as an integral flat unit which may be implanted in a particularly advantageous manner and with a minimum of potential complication and which, further, has a long lifetime over a sufficiently long period of time. 
   According to an improvement of the invention, the converter means is affixed to the plastic material body by gluing, by bonding to the metallic strip conductors and/or by injection-molding same with a plastic material mass. 
   By doing so, a long-lasting and permanent attachment of the converter means on the plastic material body may be achieved, together with a good sealing to the exterior. 
   According to a preferred embodiment of the invention, the plastic material body is manufactured from polyimide, polymethylmetacrylate (PMMA) or epoxy resin. Likewise, these materials may be utilized for embedding the chip and/or for embedding the converter means by injection-molding. 
   These materials are well-suited from a biological point of view, wherein polyimide and PMMA are particularly preferred. 
   The plastic material body together with the isolation layer is manufactured with a thickness of about between 5 and 15 micrometers, preferably about 10 micrometers. 
   Accordingly, the receiver coil as well as the chip and the necessary leads may be housed in a thin foil-type body which is well-suited for implantation purposes. 
   Accordingly, the strip conductors have a thickness of about between 0.5 and 2 micrometers, preferably of about 1 micrometer. 
   These dimensions have turned out to be sufficient for a reliable electrical connection. 
   The strip connectors are preferably generated by vapor deposition or sputtering, respectively, allowing an advantageous manufacture. Preferably, they consist of gold, titanium, platinum, iridium, aluminum, or copper. 
   It goes without saying that the features mentioned before and those that will be mentioned hereinafter cannot only be used in the particularly given combination but also in other combinations or alone without leaving the scope of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features and advantages of the invention become apparent from the subsequent description of preferred embodiments with reference to the drawings. 
       FIG. 1  shows a perspective view of a dissected eye with introduced retina implant; 
       FIG. 2  shows a view on the retina implant in a slightly modified embodiment, on an enlarged scale; 
       FIG. 3  is a cross-sectional view on the annular area of the implant along the line III—III on an enlarged scale; 
       FIG. 4  shows the annular area of  FIG. 3  when assuming a curved shape under a bending load; 
       FIG. 5  shows a portion of the annular area of the implant, on a still more enlarged scale as compared to  FIG. 3 , and 
       FIG. 6  shows a schematic cross-sectional view through an eye with the introduced implant. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In  FIGS. 1 and 6  an eyeball into which an implant according to the present invention shall be introduced, is designated as a whole by  10 . Eyeball  10 , at its front side, has a cornea  11  and, further, a sclera  12 . The limbus corneae, i.e. the rim of cornea  11 , is designated by  16  in FIG.  1 . Moreover,  FIG. 1  shows lateral eye muscles  14  and  15 . 
   At the front portion of eyeball  10 , lateral eye muscle  13  was severed by a cut. A retina implant according to the present invention, being designated as a whole by  30 , has an annular portion  32  and an extension  33  adjoining the latter. A chip for subretinal implantation is located at the outer terminal end of extension  33 , as may be seen in further detail in FIG.  2 .  FIG. 1  shows that the retina implant was positioned around lateral eye muscle  13  with its annular portion  32  and was pushed into the subretinal space with its flat extension  33  through a sclera incision  20 . 
   The design and the manufacture of the retina implant will be described hereinafter in further detail with reference to  FIGS. 2 through 5 . 
     FIG. 2  shows the retina implant in a top plan view and on an enlarged scale. As a modification with respect to the embodiment of  FIG. 1 , a strain relief is, further, provided, as will be explained hereinafter. 
   Retina implant  30  comprises a receiver coil  37  for receiving electromagnetic energy (rf energy), irradiated thereinto, a converter means  35 , for rectifying and smoothening alternating current induced into receiver coil  37  and, as the case may be, stabilizing on a predetermined voltage, as well as the chip  36  for subretinal implantation. 
   Converter means  35  which, due to the necessary smoothing capacitors, has a certain demand for space, is, therefore, configured as a unit separated spatially from chip  36 . Converter means  35  is positioned at the beginning of flat extension  33  adjacent annular area  32 . Converter means  35  consists, for example, of rectifiers, smoothing capacitors and rechargeable thin film batteries, respectively, and a voltage stabilizer. Moreover, it may comprise components for decoding and processing of information signals transmitted together with the electromagnetic energy, for example of reference signals indicative for ambient brightness. 
   The retina implant comprises a flat plastic material body  31  consisting, preferably, of polyimide. Plastic material body  31  receives various components or these components are affixed thereto. A central opening or recess is provided within annular area  32  of plastic material body  31 . Central opening  34  has a diameter d 1  of about between 8 and 16 mm. The outer diameter d 2  of the annular portion is about between 12 and 20 mm. Receiver coil  37  is received within annular portion  32 . The windings thereof are indicated as an example at  38  in FIG.  2 . The ends of receiver  37  which, as may be taken from  FIG. 2 , may comprise a zig-zag-shaped or meander-shaped tongue, are connected to converter means  35 . Converter means  35  is connected to chip  36  via connection leads  41 . Chip  36  is embedded into plastic material body  31  at the outer end of flat extension  33 . It goes without saying that its active surface which is supposed to stimulate cells, lies free. In order to simplify the attachment of implant  30  on eyeball  10  in its final position, annular portion  32  and flat extension  33  are provided with lugs  49  and  50 , respectively. As may further be taken from  FIG. 2 , flat extension  33  in its portion being intended to be pushed into the subretinal space at a later point in time, is provided with a plurality of perforations  52 . The perforations  52  are preferably arranged along an array of about between 0.1 and 1 mm width and have a diameter of about between 20 and 200 μm. By doing so, a diffusion of nutrients and oxygen between the pigment epithelium and the retina in enabled, thus avoiding negative effects that might result if the implant consisted of an impermeable material. 
   Annular portion  33  receiving receiver coil  37  is preferably subdivided into a plurality of ring-shaped sections  51  in a circumferential direction, as may be seen from  FIGS. 3 and 4 . Sections  51  are arranged coaxially one relative to the other, are separated by gaps  42  and are mechanically and electrically interconnected via radial fins  43 . 
   Each of these sections  51  contains a plurality of windings  38  and has, for example, a width of the order of about 0.5 mm, whereas the entire width is of the order of between 3 and 4 mm. 
     FIG. 3 , as an example, shows an individual radial fin  43  between the two outer sections  51 . Radial fin  43  mechanically connects the two adjacent sections  51  and also allows the electrical connection between neighbored windings  38 . The connection to inner sections  51  is likewise effected through radial fins  43  which are preferably arranged at other positions of the annular portion in an angularly offset manner for obtaining a maximum flexibility of receiver coil  37  because plastic material body  31 , as will be explained hereinafter, is manufactured as a planar body which, however, shall be applied to the surface of the bulged eyeball without folds or wrinkles and, hence, consists of a plastic material. Additionally, it is possible to bring the isolated sections  51  into a spherical shape after the plastic material body has been fully manufactured, with the spherical shape corresponding to the bulge of the eyeball. It may, for example, be fixated in this bulged shape by molding with silicon, so that the manipulation is simplified during the subsequent implantation. 
   The retina implant may, for example, be manufactured as follows: 
   First, a thin plastic material layer  44  (see FIG.  5 ), that may consist, for example, of polyimide, PMMA or epoxy resin, is laminated or spun onto a planar auxiliary substrate  53 , for example a wafer of glass, silicon or ceramic. The auxiliary substrate  53  may, for example, also be a metal foil. 
   After having generated the thin plastic material layer or foil  44  on the surface of auxiliary substrate  53 , metallic strip conductors  45  are generated on the surface of foil  44 . For that purpose, the metal, for example gold, titanium, platinum, iridium, aluminum or copper, is vapor-deposited or sputtered onto the surface. Thereby, all metallic strip conductors  45 , i.e. the windings  38  of receiver coil  37 , the connections between the individual sections  51  of receiver coil  37 , the connection leads leading to the converter means  35  via strain relief  40  as well as connection leads  41  into connecting converter means  35  and chip  36 , which is finally effected by a subsequent photolithographic microstructuring. A bridge  39  extending from the inner end of receiver coil  37  to its outside must be connected separately. Chip  36  and converter means  35  are affixed to surface  47  of foil  44 , for example by conductive gluing or bonding. An isolating layer is deposited for entirely isolating strip conductors  45 . The isolating layer may consist of the same plastic material as the plastic material that had first been deposited on auxiliary substrate  53 , i.e. polyimide or PMMA. 
   Subsequently, the body that has so been generated is separated again from auxiliary substrate  53 . Depending on the geometric conditions, chip  36  and converter means  35  may be attached to the plastic material body  31  by conductive gluing or bonding after depositing isolation layer  46  onto foil  44 . 
   The gaps  42  between neighbored sections  51  of receiver coil  47  and the meander-shaped strain relief  40  may also be generated in the course of the photolithographic microstructuring. 
   In contrast, perforations  52  within flat extension  33  are preferably generated by laser drilling. 
   The individual sections of receiver coil  37  may, further, be molded with silicon to assume a spherical shape being adapted to the bulge to the bulge of an eyeball. 
   Metallic strip conductors, preferably, have a thickness of about between 0.5 and 2 micrometers, preferably of about 1 micrometer. 
   After the depositing of isolating layer  46 , receiver coil  37  together with foil  44  have a combined thickness y of about 10 micrometers. 
   Retina implant  30  may be implanted as follows: 
   After opening the conjunctiva at the rim of cornea  11  at the temple-oriented portion of eyeball  10 , a rein thread is applied and the eye is rolled to the inside. The conjunctiva is then shifted laterally, as a lobe as the case may be. A holding thread is applied to the muscle rudiment at the rudiment of the straight lateral eye muscle  13  and the muscle is then severed and flipped laterally together with the holding thread. A sclera incision  20  is then made into the sclera somewhat below the lateral eye muscle, either above or, as shown in  FIG. 1 , slightly below eye muscle  13 . A small quadrangular lobe  21  is then cut in a wing shape and is flipped downwardly. 
   Holding threads are now applied through the corners of lobe  21  and the lobe is then flipped rearwardly as shown in FIG.  1 . Under the application of haemostatic agents, the choroid  22  below sclera  12  and the pigment epithelium are now opened along a slit (see  FIG. 6 ) without perforating the retina  19  itself. The end of the extension  33  carrying chip  36  is now pushed into the choroid slit and advanced into the subretinal space, as the case may be under the control of a fiber optic, until about four fifth of the extension are within the eye  10  and the end thereof together with chip  36  have assumed their final position. As the case may be, the channel may be opened before with a flexible plastic material spatula similar to the extension of retina implant  30  by lifting retina  19  somewhat away from the pigment epithelium. 
   As soon as the terminal end carrying chip  36  has assumed its final position in the macula area, it is affixed in that position on the sclera by pulling two plastic material threads through the small perforated holes in the lugs  50  at extension  33  and by attaching same on the sclera with individual knots. The annular portion  32  together with receiver coil  37  is similarly attached by means of two more individual head seams drawn through perforations on the lugs  49  of the receiver coil  37  opposite extension  33 . Receiver coil  37  is positioned such that the root of lateral straight eye muscle  13  on its eyeball side is located within opening  34  of annular portion  32 . 
   Thereafter, wing-shaped lobe  21  of sclera  11  is closed at its two corners with two further single head seams. Thereafter, the lateral straight eye muscle  13  is again pulled forwardly by means of the holding thread and is then attached to its original root over annular portion  32  by means of muscle seems. Subsequently, the conjunctiva is then again attached by means of a few single head seams and the rein thread is removed. After the position of the chip and the fundus conditions have been examined by means of direct and indirect ophthalmoscopy, an ointment dressing is applied.