Abstract:
The present invention relates to retinal prostheses, and in particular to the transfer of electrical power and data from outside of the human body to such a prosthesis. The retinal prosthesis comprises: A retinal electrode array implanted in the eye to stimulate the retina. A receiving coil implanted sub-sclerally to inductively receive power or data signals, or both. An electrical connection between the implanted receiving coil and the implanted retinal electrode array. Wherein the receiving coil is flexible and able to conform to scleral curvature, when it is implanted. And wherein power or data signals, or both, received by the receiving coil from a remote transmitting coil are automatically provided to the electrode array. According to a second aspect, the present invention provides a method for implanting a retinal prosthesis. In a further aspect the present invention further provides an ocular implant.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a division of application Ser. No. 13/266,317 filed Oct. 26, 2011 for Retinal Prostheses which is a national application of PCT application number PCT/AU2010/000474 filed Apr. 23, 2010 for Retinal Prosthesis, which claims priority from Australian application number 2009/901812 filed Apr. 27, 2009 for Retinal Prosthesis. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to retinal prostheses, and in particular it relates to the transfer of electrical power and data from outside of the human body to such a prosthesis. 
         [0004]    2. Description of Related Art 
         [0005]    A retinal prosthesis which uses electrical signals to stimulate the retina requires electrical power to function. The power demands of retinal prostheses are likely to increase as higher density electrode arrays are developed in future. A retinal prosthesis cannot practically be powered by wires from an external power supply, as any wired connection through the skin creates a risk of infection and causes discomfort to the user. Previous proposals for powering retinal prostheses include the use of optical and acoustic energy, however these solutions are ineffective due to high losses when these energy types pass through tissue. 
         [0006]    Inductive coupling links have also been proposed for visual prostheses. Such proposals provide for an external primary coil which is placed in front of the eye, and a secondary internal coil inside the eye. However, the large separation between these coils and the small diameter of the internal coil result in low power transfer efficiency. 
         [0007]    Surgical implantation of a prosthesis into the eye also presents particular difficulties due to the need to ensure ongoing integrity of the ocular structure, at least after surgical healing is complete. For example the sclera provides resistance to forces on the eye, helps to maintain intraocular pressure, and helps resist infection within the eye. Any implanted device must also be structured and positioned in a way to allow for the normal range of motion of the eyeball and the almost continual nature of eyeball movement. 
       SUMMARY OF THE INVENTION 
       [0008]    According to a first aspect the present invention provides a retinal prosthesis, comprising: 
         [0009]    A retinal electrode array implanted in the eye to stimulate the retina. 
         [0010]    A receiving coil implanted sub-sclerally to inductively receive power or data signals, or both. 
         [0011]    An electrical connection between the implanted receiving coil and the implanted retinal electrode. 
         [0012]    Wherein the receiving coil is flexible and able to conform to scleral curvature, when it is implanted, and wherein power or data signals, or both, received by the receiving coil from a remote transmitting coil are automatically provided to the electrode array. 
         [0013]    The sub-scleral positioning of the receiving coil enables a retinal prosthesis to be implemented which has no wiring or tethers from the intraocular devices to the extraocular space. This allows for complete healing of the sclera after the device is implanted, which allows the sclera to perform its role providing a barrier to intraocular infection. 
         [0014]    The retinal electrode array may be sub-retinal, for instance it may be located epi-retinally near the fovea in the macular region of the retina. 
         [0015]    One or more retinal self-locking tacks may be used to mechanically secure the electrode array in the epi-retinal position. A retinal tack may also complete an electrical connection between the secondary coil and the electrode array. The retinal tack may be formed of an insulating material, such as a ceramic, and house a conductor that spans electrical contacts at each end of the tack. 
         [0016]    In one example the retinal tack may be arranged to conduct power or data signals, or both, from the secondary coil through the choroid or retina, or both, to the electrode array. The insulating material of the retinal tack may minimize electrical current leakage between the secondary coil and the electrode array. The conductor of the retinal tack may carry data signals in both directions, to and from the retinal array. 
         [0017]    Other locations for the retinal electrode array are also possible, for instance in the suprachoroidal space. 
         [0018]    The receiving coil (generally nominated the ‘secondary’ coil below) may be intrinsically flexible. Alternatively, it may be formed or mounted on a flexible substrate. 
         [0019]    The receiving coil may be located between the sclera and the choroid. It may be located supra-choroidally and epi-sclerally. 
         [0020]    The present invention thus provides for an implanted secondary coil which does not require a full sclerotomy, and as a result does not result in an interconnect piercing the sclera. 
         [0021]    The receiving coil may be connected to the electrode array by the use of flexible wiring. The flexible wiring may be implanted sub-sclerally (in the suprachoroidal layer) between the coil and the array (or a retinal tack). Alternatively, the wiring from the receiving coil may intrude through the choroid and the vitreous humor to the array. In this case it is preferred that the wiring does not pass through any part of the retina. 
         [0022]    The receiving coil may receive power and data signals by inductive coupling with a transmitting coil. 
         [0023]    The remote transmitting (primary) coil may be located externally to the body, for instance mounted on the surface of the skin. 
         [0024]    In some situations it may be necessary or desirable to use one or more additional, intermediate coils to relay power or data signals, or both, from the remote transmitting (primary) coil to the receiving (secondary) coil. For instance a first intermediate coil may be implanted in the zygomatic bone for receiving power from an external primary coil. A second intermediate coil may be implanted in the orbit of the ocular region for inductively relaying power from the first intermediate coil to the secondary. The first and second intermediate coils may be in wired connection, which improves transmission efficiency. 
         [0025]    According to a second aspect, the present invention provides a method for implanting a retinal prosthesis, comprising:
       Implanting a retinal electrode array in the eye.   Implanting a flexible receiving coil sub-sclerally, wherein the receiving coil is flexible and able to conform to scleral curvature when it is implanted.       
 
         [0028]    Electrically connecting the retinal electrode array to the implanted receiving coil, such that power or data signals, or both, received by the receiving coil from a remote transmitting coil are automatically provided to the electrode array. 
         [0029]    In a further aspect the present invention further provides an ocular implant, comprising: 
         [0030]    A receiving coil for implanting sub-sclerally to inductively receive power or data signals, or both. 
         [0031]    A retinal electrode array. 
         [0032]    Flexible wiring interconnecting the receiving coil and the electrode array. 
         [0033]    Wherein the receiving coil and the wiring are flexible and at least the receiving coil is able to conform to scleral curvature, when implanted. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    The exact nature of this invention, as well as the objects and advantages thereof, will become readily apparent from consideration of the following specification in conjunction with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein: 
           [0035]      FIGS. 1(   a ) and  1 ( b ) are diagrams that illustrate the anatomical positioning of a secondary coil for effecting an inductive power link to a retinal implant; 
           [0036]      FIG. 2(   a ) is a diagram that illustrates the location of an external primary coil; 
           [0037]      FIG. 2(   b ) is a diagram that illustrates the relative locations of the external primary coil of  FIG. 2(   a ), two internal intermediate coils, and the internal secondary coil of  FIGS. 1 ; 
           [0038]      FIG. 3(   a ) is cross-section of an eye from the side, showing the location of a retinal electrode array and the relative locations of the external primary coil and the internal secondary coil that are in front of the plane of the section, and the route of the flexible wiring interconnecting the internal secondary coil and the retinal electrode array; 
           [0039]      FIG. 3(   b ) is a magnified section through the layers of the eyeball showing the locations of the internal secondary coil and the flexible wiring connected to it; 
           [0040]      FIG. 3(   c ) is a magnified section through the layers of the eyeball of  FIG. 3(   b ) showing the locations of the retinal electrode array, a retinal tack and the flexible wiring from the internal secondary coil; 
           [0041]      FIG. 4(   a ) is cross-section of an eye from the side, showing the location of a retinal electrode array and the relative locations of the external primary coil and the internal secondary coil that are in front of the plane of the section, and an alternative route of the wiring interconnecting the internal secondary coil and the retinal electrode array; 
           [0042]      FIG. 4(   b ) is a magnified section through the layers of the eyeball of  FIG. 4(   a ) showing the locations of the internal secondary coil and the wiring connected to it; 
           [0043]      FIGS. 5(   a ) and ( b ) show a variation of the arrangement of  FIG. 4  where the internal secondary coil is mounted on a flexible scleral buckle that is positioned episclerally; 
           [0044]      FIG. 6  is a diagram of the eyeball showing the location of the surgical incision required for a trans-vitreous connection to be made between the internal secondary coil and the retinal electrode array; 
           [0045]      FIG. 7  is a variation on  FIG. 2(   b ) where there is only a single intermediate coil; 
           [0046]      FIG. 8(   a ) is a diagram of a first configuration for a power transfer coil; 
           [0047]      FIG. 8(   b ) is a diagram of a second configuration for a power transfer coil; and 
           [0048]      FIG. 8(   c ) is a diagram of a third configuration for a power transfer coil. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0049]    Referring first to  FIGS. 1(   a ) and  1 ( b ), these diagrams illustrate the anatomical location of a secondary coil  110  for effecting an inductive power link to a retinal implant (not shown).  FIG. 1(   a ) shows the eye ball from the front, and  FIG. 1(   b ) from the side, with the pupil  10 , iris,  20  and the sclera (white of the eye)  30 . The bony structure around the eye is also indicated at  40  in  FIG. 1(   a ), as is the zygomatic bone  50 , the nose  60  and the skin on the temple  70 . Several muscles that move the eye (such as the ciliary muscle  80 ) are also shown in both drawings but they are not important for understanding the location of the secondary coil  110 . The secondary coil is shown at the side of the eye but is implanted beneath the sclera  30 , and would not be visible to an observer. 
         [0050]      FIG. 2(   a ) illustrates the location of an external primary coil  120 , close to the temple. The primary coil  120  is located externally on or near the skin  70 , and is connected to a power source (not shown). The secondary coil  110  is connected to a retinal implant (not shown) inside the eye and is located on a flexible substrate, that is implanted at a location under the sclera. 
         [0051]    An inductive link operates by a time-varying electrical current flowing in a primary coil inducing a current in a secondary coil, provided it is located in sufficiently close proximity to the primary coil. In this case, the primary coil  120  is located outside the eye, while the secondary coil  110  is placed inside the eye. The primary coil  120  is connected to a power source via an electrical connection and electronics that drive the current in the coil. The secondary coil  110  is connected to an implanted device via electronics which recover the energy from the inductive link to supply power to the implant. The inductive link removes the need for a physical (wired) electrical connection between an external power source and the implanted device. 
         [0052]    An inductive power link for a retinal prosthesis, must take into account the fact that the secondary coil  110  is constrained by the physical and biological environment of the eye, and the high power consumption of the implanted device. The aim is to deliver the required power without exceeding safety limits. 
         [0053]    The secondary coil  110  is formed or mounted upon a flexible substrate which is surgically implanted in the supra-choroidal space. In particular the secondary coil  110  is provided on a thin flexible circuit, or substrate, much like a scleral buckle. This entire device is surgically implanted under the sclera, between the sclera and the choroid in the suprachoroidal space. Furthermore, the secondary coil is located near the ciliary muscle  80  (see  FIG. 1(   b )), away from the retina, to prevent injury to the delicate retina  400  layer. 
         [0054]      FIG. 2(   b ) illustrates the relative locations of the external primary coil  120 , two internal intermediate coils  130  and  132 , as well as the internal secondary coil  110 . The intermediate coils  130  and  132  are used to improve the power transfer efficiency between the primary coil  120  and the secondary coil  110 . The first intermediate coil  130  sits on the zygomatic bone  50  of the skull immediately adjacent the external primary  120 . The second intermediate coil  132  sits in the orbit of the ocular region immediately adjacent the secondary  110 . These two coils are in circuit with each other via a hole  90  through the zygomtic bone. 
         [0055]    Due to the relatively small distance between the secondary coil  110  and the second intermediate coil  132 , and the relatively small distance between the primary coil  120  and the first intermediate coil  130 , more efficient power transfer can be achieved. Moreover, such efficiency is achieved in a manner which provides wireless power transfer through the sclera  30 , allowing the sclera to be maintained intact once healed from implantation surgery. Further, the relative positioning of second intermediate coil  132  and secondary  110  allows for normal movement of the eyeball, while maintaining high power transfer efficiency which is relatively unsusceptible to movements of the eye. 
         [0056]    The retinal electrode array  150  is implanted epi-retinally near the fovea in the macular region of the retina. The retinal array is held in place by a self-locking retinal tack  160 , seen in  FIG. 3(   c ). Also shown in  FIG. 3(   c ) are a number of retina stimulating electrodes  152  extending from the back of the electrode array  150  into the tissue of the retina. 
         [0057]    Power is transferred from the secondary coil  110  to the retinal electrode array  150  by a physical connection comprising flexible circuit wiring  140 . In  FIGS. 3(   a ) and ( b ) the flexible circuit wiring  140  is disposed along the suprachoroidal space between the secondary coil  110  and the retina, where is passes behind the retinal electrode array  150 . To connect the power from the wiring  140  in the suprachoroidal space through the choroid  300  and retina  400  to the implant  150 , it passes through a conductive path in the retinal tack  160 . 
         [0058]    The use of a retinal tack to both mechanically anchor the implant  150 , and also provide an electrical connection from the wiring  140  to the implant, minimizes the number of components piercing the retina  400  and choroid  300 . 
         [0059]    It is envisaged that more than one tack may be required to adequately anchor implant  150 . In the case where more than one tack  160  is used, some or all of the tacks may provide electrical connections to the wiring  140 . 
         [0060]    In order to prevent current leakage from the conductive path of the retinal tack  160 , it is sheathed in non-conductive ceramic from the contact point  142  between the tack  160  and the flexible wiring  140 . The conductor (not shown) of the retinal tack  160  then efficiently conveys power, and if required a data signal, from the electrical wiring  140  to the retinal implant  150  with minimal leakage. The power and data received by the electrode array  150  enables electrical stimuli to be applied via electrodes  152  to the nerve cells in the retina. 
         [0061]    In order to locate the inductive coils  110 ,  120 ,  130  and  132  in and near the eye, the following surgical procedure is followed: 
         [0062]    First, the flexible wiring  140  is inserted into the suprachoroidal space near the macular region of the eye. 
         [0063]    Next, the secondary coil  110  is placed under the sclera  30 . 
         [0064]    Once the sclera  30  has recovered reasonably well, the retinal implant unit  150  is inserted by performing an incision at the pars plana region and securing it in place with the self-locking tacks  160 . 
         [0065]    Next, the intermediate coils  130  and  132  are anchored to the zygomatic bone with one coil in the ocular region and the other coil under the skin. 
         [0066]    The intermediate coils  130  and  132  are connected via a physical wire which passes through a hole bored through the zygomatic bone, as shown in  FIG. 2(   b ). 
         [0067]    A wireless power link is then established from the intermediate coil  130  to the primary coil  120 , outside the body. The primary coil could be carried by, or encased within, the frame of a pair of spectacles, as shown in  FIG. 2(   a ). 
         [0068]    The sub-scleral positioning of the secondary coil  110  enables a retinal prosthesis to be implemented which has no wiring or tethers from the intraocular device to the extraocular space. This arrangement allows the sclera  30  to completely heal after surgery, and return to its normal roles such as providing a barrier to intraocular infection and the like. 
         [0069]    In some applications the interface between the retinal tack  160  and the flexible wiring  140  may suffer from long term reliability problems. These might be addressed by the implantation of a pre-connected and fully sealed connection between the two; rather than the use of retinal tacks. 
         [0070]    This might be achieved by use of a trans-vitreous link as shown in  FIGS. 4(   a ) and  4 ( b ). In this variation flexible wiring  170  extends from the secondary coil  110  through the vitreous humor directly to a connection  172  on the exposed surface of the implanted device  150 . This allows the electrical connection  172  between the flexible link  170  and the implant  150  to be fabricated in an integrated manner before implantation, and therefore will be highly reliable. 
         [0071]    Another alternative involves placement of an intermediate coil onto the outer surface of the sclera  30 . This effectively eliminates any relative motions between the secondary coil  110  and the intermediate coil  132  due to eye movements. This increases the efficiency of the inductive link since wireless power transfer is dependent on the amount of overlap between the coils. 
         [0072]    In the event that it is necessary for a transcleral link to be made, it is beneficial to run the link through the sclera  30 , along between the sclera and the choroid  300  and then through the choroid, rather than penetrating directly through both layers of the eyeball. The link could run under the sclera  30  for up to half the perimeter of the eyeball before penetrating the choroid  300 . This separation of the puncture through the sclera  30  and choroid  300  reduces the possibility of inner ocular infection and assists post-surgical recovery. For instance the secondary coil  110  could be mounted on a sclera buckle  112  and the assembly be placed epi-sclerally, as shown in  FIG. 5 . The benefit of placing the secondary coil  110  epi-sclerally is to enable a larger diameter coil to be realized, thus improving power transfer efficiency between the primary and secondary coils. Depending on the size of the secondary coil, this modification can potentially replace the need for an intermediate coil. 
         [0073]    In order to implant the devices described with reference to  FIGS. 4 and 5 , the following surgical procedure maybe performed: 
         [0074]    A sclera flap  500  is cut above the lateral eye muscle and the flab folded backward to expose the choroid  300  below. 
         [0075]    An incision  502  on the choroid  300  is then made, as shown in  FIG. 6 . The location of this incision should be made close to the pars plana region away from the retina  400  layer to avoid damage to the retina. 
         [0076]    The implant  150  which has been integrated into the flexible trans-vitreous link  170  beforehand is then inserted through the incision. 
         [0077]    Once the insertion is complete, the sclera flap  500  is closed. In the case of  FIG. 4(   a ), closure of flap  500  is achieved by it being sutured back to the surrounding sclera  30  and fully sealed; as shown in  FIG. 4(   b ). For the arrangement of  FIG. 5(   a ), it is necessary to leave part of the flap open to allow for a trans-scleral link  171  to be connected to the secondary coil  110  which is mounted on the scleral buckle  112 . 
         [0078]    Another alternative arrangement involves the use of a single intermediate coil  180  placed between the skin and the zygomatic bone, in the vicinity of a primary  120  and a secondary  110 ; see  FIG. 7 . 
         [0079]    Many different configurations are possible for the power transfer coils  110 ,  120 ,  130 ,  132 ,  180 . Generally, a coil consists of a continuous conductive track which spirals outwards resulting in a number of turns. The shape of the coil may be circular, oval or oblong as depicted in  FIGS. 8(   a ), ( b ) and ( c ) respectively. The amount of required power transfer and ease of surgical procedure are factors that are taken into account when determining the size and shape of the coils. 
         [0080]    It will be appreciated that a sympathetic combination of coil configuration and location, surgical and patient friendly design, and reliable mechanical and electrical connections are required to implement feasible inductive power transfer to a retinal implant. 
         [0081]    It will also be appreciated by those skilled in the art that numerous variations and modifications may be made to the invention as described above without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.