Abstract:
An artificial retinal device, implanted in the subretinal space of the eye in persons with certain types of retinal blindness, induces artificial vision by electrical stimulation of the remaining viable cells of the retina. The artificial retina device includes a stimulating electrode unit preferably placed in the subretinal space.

Description:
PRIORITY CLAIM 
     This application is a continuation of U.S. patent application Ser. No. 10/142,277, filed on May 9, 2002, now U.S. Pat. No. 7,003,354 which is a continuation of U.S. patent application Ser. No. 09/564,841, filed on May 4, 2000, now issued as U.S. Pat. No. 6,427,087 on Jul. 30, 2002, all of which are herein incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention is generally directed to medical devices. More particularly, the present invention is directed to an artificial retina medical device and method to more efficiently stimulate electrically and with higher resolution, neuroretinal cells in partially damaged retinas to produce artificial vision. The invention provides improved efficiency and resolution of the device by using transretinal electrical current stimulation provided by stimulation and ground return electrodes that are disposed on opposite sides of the neuroretina. 
     BACKGROUND 
     A variety of retina diseases cause vision loss or blindness by destruction of the vascular layers of the eye that include the choroid and choriocapillaris, and the outer retinal layers that include Bruch&#39;s membrane and retinal pigment epithelium. Loss of these layers is often accompanied by degeneration of the outer portion of the neuroretina, typically the photo-receptor layer. Variable sparing may occur of the remaining neuroretina composed of the outer nuclear, outer plexiform, inner nuclear, inner plexiform, ganglion cell and nerve fiber layers. 
     Known prior efforts to produce vision by retinal electrical stimulation used arrays of stimulating electrodes with their ground return electrode or electrodes disposed either entirely on the epiretinal or the subretinal side of the neuroretina. Placement of stimulating and ground return electrodes together in this fashion resulted in inefficient stimulation of the neuroretina because the electrical field was not forced directly through the neuroretina. Resolution was also degraded because of diffuse spreading of each stimulating electrode&#39;s electrical field. 
     BRIEF SUMMARY OF THE PREFERRED EMBODIMENTS 
     The artificial retina device of this invention is preferably composed of two basic units, the stimulating electrode unit and the ground return electrode unit. In one embodiment, the two units are physically and electrically continuous, or physically and electrically connected by an insulated tail-like conductor that in some embodiments supports, positions, and aligns the two units on opposite sides of the neuroretina relative to each other. The stimulating electrode unit is, for example, a silicon disk 3 mm in diameter and 25 microns thick, and is comprised of separated stimulating microelectrode subunits. Preferably, the stimulating electrode unit has a ground return electrode unit extending from one edge, comprised of a silicon tail with an insulated conductor leading to the ground return electrode at its tip. The stimulating microelectrode subunits of the stimulating electrode units deliver current generated by one or more microphotodiodes connected, for example, in series and fabricated within the subunit. The preferred number of microphotodiodes per subunit is one. 
     In some embodiments, the stimulating electrode and ground return electrode are configured to be disposed on opposite sides of the neuroretina. For example, in some embodiments, the ground return electrode is disposed on the outside of an eye. In other embodiments, the ground return electrode is disposed on a scelra surface outside of an eye. In further embodiment, an electrical source is connected with the stimulating electrode, the ground return electrode, or both. 
     In other embodiments, each microelectrode subunit is preferably fabricated on a node of a disk-shaped silicon web, the subunits separated by open areas of the web. The open areas of the web allow nourishment and oxygen from the outer retinal circulation to diffuse into the neuroretina. 
     In the preferred embodiment, on the backside of the stimulating electrode unit, i.e. the side opposite the incident light side, an insulated common conductor is constructed and arranged to electrically ground the microelectrode subunits. The common ground conductor preferably continues along the length of the ground return electrode unit and terminates in an exposed ground return electrode at or near the tip of the ground return electrode unit, and disposed in the vitreous cavity. The exposed ground return electrode tip in the vitreous cavity allows the electrical field generated by the microelectrode subunits in the subretinal space to transretinally stimulate the neuroretina. 
     In a second embodiment, an additional tail with an embedded conductor and an electrode tip is connected to the ground electrode tip of the ground electrode unit to extend the location of the ground electrode further into the vitreous cavity. 
     In a third embodiment, the conductor of the ground electrode unit is electrically connected with an additional bias photodiode or photodiodes to increase the voltage and current generated by the device. In this latter case, the ground electrode of the device is preferably disposed on the additional bias photodiode or photodiodes disposed in the vitreous cavity. 
     In a fourth embodiment, the bias photodiode or photodiodes are placed in the lens capsular bag of the eye after surgical removal of the lens nucleus and cortical material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the invention will be apparent to those skilled in the art with reference to the detailed description and the drawings, of which: 
         FIG. 1A  is a plan view of a preferred embodiment showing the stimulating electrode unit and the ground return electrode unit. 
         FIG. 1B  is a side view of  FIG. 1A  showing the stimulating electrode unit and the ground return electrode unit. 
         FIG. 2A  is a plan view of the tail extension of the preferred embodiments, that physically and electrically couples to the ground return electrode unit of  FIGS. 1A and 1B  to extend the location of the ground return electrode further into the vitreous cavity of the eye. 
         FIG. 2B  is a cross-sectional view of the tail extension of the preferred embodiments. 
         FIG. 3  is a perspective view showing the tail extension of  FIGS. 2A and 2B  attached to the ground return electrode unit of  FIGS. 1A and 1B . 
         FIG. 4  is a perspective view of another embodiment, showing the stimulating electrode unit fabricated as a circular silicon web to allow nourishment to flow between the choroid and the neuroretina, and the stimulating electrode subunits fabricated at the intersecting nodes of the web. 
         FIGS. 4A and 4B  are magnified plan and sectional views respectively of the embodiment of  FIG. 4  where the stimulating electrode subunits of the stimulating electrode unit are each comprised of three microphotodiodes electrically connected in series to increase the voltage output of each stimulating electrode subunit. 
         FIG. 5  is a cross-sectional view of  FIGS. 1A and 1B , in the eye with a stimulating electrode unit in the subretinal space and a ground return electrode of the ground return electrode unit exposed in the vitreous cavity. 
         FIG. 5A  is a block diagram illustrating some layers of the eye. 
         FIG. 6  is a cross-sectional view of the device of  FIG. 5  with the attached tail extension of  FIGS. 2A and 2B . 
         FIG. 7  is a cross-sectional view of another embodiment, showing the device of  FIGS. 1A and 1B  with an electrode stimulating unit implanted in the subretinal space and a ground return electrode loop of the ground return electrode unit disposed in the vitreous cavity. 
         FIG. 8  is a cross-sectional view of another preferred embodiment, showing the device of  FIGS. 1A and 1B  with a stimulating electrode unit implanted in the subretinal space and a tail extension electrically connecting to a bias photodiode disposed in the lens capsule of the eye, the bias photodiode containing the extended location of the ground return electrode, and the bias photodiode providing additional voltage and/or current to the electrode stimulating unit in the subretinal space. 
         FIG. 9  is a cross-sectional view of another embodiment, showing the device of  FIGS. 1A and 1B  with its stimulating electrode unit implanted in the subretinal space and a tail extension electrically connecting to a bias photodiode disposed in front of the iris, in the anterior chamber of the eye, the bias photodiode containing the extended location of the ground return electrode, and the bias photodiode providing additional voltage and/or current to the electrode stimulating unit in the subretinal space. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, as shown in  FIGS. 1A and 1B , the preferred embodiment of retinal device  10  has a stimulating electrode unit  12  and a curved ground return electrode unit  16  configured for implantation into an eye such that the retinal device may be positioned completely inside the eye and stimulate opposite or substantially opposite sides of the neuroretina. The two components  12  and  16  are preferably physically fabricated on a single thin silicon chip substrate  11 , but may be fabricated separately and then joined together. The stimulating electrode unit  12  includes an array of stimulating electrode subunits  22  each composed of one or more electrical sources such as a photodetector or photodetectors. In a preferred embodiment, the photodetectors may be implemented as microphotodiodes  23   a  electrically connected, for example, in series. 
     A stimulating electrode  23   b  contacts at least one of individual cells, groups of cells, portions of cells and nerve fibers of the neuroretina. The ground return electrode  14  is preferably disposed at or near the tip of the ground return electrode unit  16 . The stimulating electrode  23   b  and ground return electrode  14  are disposed on opposite sides of a neuroretina, or if the neuroretina is partially missing or damaged, then on opposite sides of the remainder of the neuroretina. In a preferred embodiment, the stimulating electrode  23   b  is disposed in a subretinal space of the neuroretina and the ground return electrode  14  is disposed on an epiretinal side of the neuroretina. In another embodiment, the positions are reversed, with the ground return electrode  14  being disposed in the subretinal space of the neuroretina and the stimulating electrode  23   b  being disposed on the epiretinal side of the neuroretina. 
     Also as shown in  FIGS. 1A and 1B , exemplary components of the preferred embodiment of retinal device  10  includes the thin silicon substrate  11 , stimulating electrode unit  12 , stimulating electrode subunits  22 , microphotodiodes  23   a  electrically connected, for example, in series, within stimulating electrode subunits  22  and an iridium/iridium oxide stimulating electrode  23   b  of stimulating electrode subunits  22 . The microphotodiodes  23   a  or other electrical source preferably provides stimulation to the neuroretina from the subretinal and vitreous cavity sides of the eye. Alternatively, The electrical source could provide stimulation from outside the eye in response to incident light. For example, the electrical source could send signals proportional to sensed incident light via hardwiring into the subretinal space and vitreous cavity of the eye. In another embodiment, the electrical source could transmit a signal in a wireless fashion to the eye using, for example, radio frequency (RF) to send signals to a coil located in the eye that is in communication with the stimulation and ground electrodes. Other known mechanisms may also be used for providing electrical energy to the eye in response to incident light. 
     Also included with the ground return electrode unit  16  is a silicon nitrite stress layer  17  that preferably shapes the ground return electrode unit  16  in a generally curved shape to direct the ground return electrode unit  16  into the vitreous cavity. Although a curve directs the ground electrode unit  16  into the vitreous cavity, other shapes could be used, such as an angled ground electrode, to perform the same function, but may be more difficult to fabricate. The ground return electrode  14  is preferably produced of an iridium/iridium oxide and includes a titanium adhesion layer  14   a  and a P+ tub  14   b  disposed under a titanium adhesion layer  14   a  to allow electrical contact with the doped silicon substrate  11 . The retinal device  10  also preferably includes a silicon dioxide layer  15  that insulates the stimulating electrode unit  12  and ground return electrode unit  16 . 
     As shown in  FIGS. 1A and 1B , the stimulating electrode unit  12  includes a plurality of stimulation electrode subunits  22  having one or more microphotodiodes  23   a  electrically connected, for example, in series within each electrode subunit  22 . The preferred number of microphotodiodes  23   a  is one unit per microelectrode subunit  22 . The layers of the microphotodiode are, for example, from the incident light surface, the iridium/iridium oxide electrode  23   b , titanium adhesion layer  23   c , N+ tub  23   d , intrinsic layer  23   e  and the silicon substrate  11 . Those skilled in the art will appreciate that other arrangements could be used where the microelectrode subunits are subunits capable of generating electrical current. 
     Also shown in  FIGS. 1A and 1B , the ground return electrode unit  16  preferably includes a positioning hole  24  that allows the retinal device  10  to be positioned with instruments during surgery. The ground return electrode unit  16  in another embodiment includes notches  26  that allow a secure fit for attachments that have corresponding protrusions that fit into the notches  26 , as described in more detail below. 
     As shown in  FIGS. 2A and 2B , a tail extension  30  is disclosed for attachment to the ground return electrode unit  16  (shown in  FIGS. 1A and 1B ) to extend the electrical termination of the ground return electrode  14  (shown in  FIGS. 1A and 1B ), for example, further into the vitreous cavity. Further extension of the ground electrode into the vitreous cavity may be required to diminish undesirable skewing of the electric field that travels from the stimulating towards the ground electrode. Such a skewed electric field is less efficient in stimulating the neuroretina compared to an electrical field that is arranged in a direction perpendicular to the neuroretinal surface. 
       FIG. 2A  is a plan view and  FIG. 2B  is a side view of the tail extension  30 . The tail extension attachment  30  is constructed of a biocompatible material  31 , such as Parylene or a similar biocompatible material and is preferably manufactured with a curve. The tail extension attachment  30  also includes an embedded conductor  34 , insulated by the surrounding material  31 , terminating in a tail extension ground return electrode  32  at or near an end of the tail extension attachment  30 , preferably to locate the electrode as far into the vitreous cavity as possible. The conductor  34  of the tail extension attachment  30  is designed to electrically contact the ground return electrode  14  when the tail extension attachment  30  is attached to the ground return electrode unit  16  (shown in  FIGS. 1A and 1B ). The tail extension ground electrode  32  is preferably constructed of iridium/iridium oxide, or other suitable electrode material. 
     Also referring to  FIGS. 1A and 1B , the tail extension attachment  30  has a pocket  36  that fits over the ground electrode unit  16  to establish electrical contact with the ground return electrode  14 . Inside the pocket  36  are protrusions  38 , which fit into the notches  26  of the ground return electrode unit  16 . The protrusions  38  are preferably constructed of a biocompatible material, such as Parylene, or a similar biocompatible material. The tail extension attachment  30  includes a slot  40  that allows the positioning hole  24  of the ground return electrode unit  16  to be access by an instrument (not shown). 
       FIG. 3  is a perspective view showing the tail extension  30  (shown in  FIGS. 2A and 2B ) electrically attached with the ground return electrode unit  16  of the retinal device  10 . The conductor  34  of the tail extension  30  contacts the ground return electrode  14  of the ground return electrode unit  16 . The tail extension  30  is preferably curved to position its ground return electrode  32  into the vitreous cavity of the eye. Those skilled in the art will appreciate that other shapes of the tail extension could be used as long as the shape positions the ground return electrode into the vitreous of the eye. The stimulating electrode unit  12  is also shown. 
       FIG. 4  is a perspective view of another embodiment of the retinal device  10  shown in  FIGS. 1A and 1B . Like components are labeled using the same reference numerals followed by a letter. Alternative embodiment retinal device  10   a  is similar to the preferred embodiment retinal device  10  shown in  FIGS. 1A and 1B , except that the stimulating electrode unit  12   a  is fabricated as a disk-shaped web  17  to allow nourishment to flow between the choroid and the neuroretina, and the stimulating electrode subunits  22   a  are fabricated at the intersecting nodes of the web  17 . Preferably, the web is manufactured of silicon and can be perforated. The alternative embodiment retinal device  10   a  is thus similar to the preferred embodiment retinal device  10  with the addition of fabricated nutrient openings  13 . 
       FIG. 4A  is a magnified plan view, and  FIG. 4B  is sectional view taken through section III-III of  FIG. 4A  of an alternative embodiment of the retinal device  10   a  shown in  FIG. 4 . The stimulating electrode subunits  22   a  of the stimulating electrode unit  12   a  shown in  FIG. 4  are each comprised of first, second, and third microphotodiodes  24 ,  25 ,  26  electrically connected, for example, in series within stimulating electrode subunit  22   a  to increase the output voltage of each stimulating electrode subunit  22   a . The stimulating electrode subunits  22   a  contact a common ground conductor  28   d  via a contact pad  28   c.    
     Preferably the common ground conductor  28   d  and contact pad  28   c  are insulated during fabrication, for example, by silicon dioxide  29  deposition. For clarity purposes, preferably only the layers of one of the microphotodiodes connected electrically in series is labeled; they are the N+ layer  24   a , the N type silicon substrate  24   b , the intrinsic layer  24   c , and the P+ layer  24   d . Conductors  27   b ,  28   b  are preferably deposited over insulating layers of silicon dioxide  27   a ,  28   a  to electrically connect the adjacent microphotodiodes  24 ,  25 ,  26 . An insulating layer of silicon dioxide  27   c  covers conductor  27   b . The stimulating electrode  27  of each stimulating electrode subunit  22   a  is preferably fabricated from iridium/iridium oxide deposited over a titanium adhesion layer. Those skilled in the art will appreciate that other electrode materials, for example, noble metals like platinum and tantalium, may be used. The common ground conductor  28   d  of the stimulating electrode subunits  22   a  terminates electrically, for example, at or near the ground return electrode  14   a  of the ground return electrode unit  16   a , shown in  FIG. 4 . 
       FIG. 5  is a cross-sectional view showing the preferred embodiment retinal device  10  of  FIGS. 1A and 1B  implanted in the eye  6  with the stimulating electrode unit  12  disposed in the subretinal space between the neuroretina  50  and the retinal pigment epithelium  52 , and the ground return electrode unit  16  in the vitreous cavity  54 . Light images  56  enter the eye  6  through the cornea  58  and lens  60  and are focused onto the stimulating electrode unit  12 . Patterned electrical stimuli are then generated by the microphotodiodes of the electrode subunits  22  ( FIG. 1A ) that stimulate the overlying neuroretina  50  in the pattern of the image. For purposes of reference, other structures of the eye  6  that are shown are an iris  62 , a sclera  64  and an optic nerve  66 .  FIG. 5A  illustrates some layers of the eye including the neuroretina  50 , the retinal pigment epithelium (RPE)  52 , the choriocapillaris  53 , the choroid  55 , and the sclera  64 . 
       FIG. 6  shows a cross-sectional view of an alternate embodiment retinal device  10   b , including the preferred embodiment retinal device  10  as described in  FIGS. 1A and 1B  and other features. The alternate embodiment retinal device  10   b  includes the stimulating electrode unit  12  disposed in the subretinal space between the neuroretina  50  and the retinal pigment epithelium  52 , and the ground return electrode unit  16  in the vitreous cavity  54 , with attached tail extension  30  of  FIGS. 2A and 2B . A purpose of the tail extension  30  is to electrically extend the location of the ground return electrode further into the vitreous cavity  54  to prevent skewing of the transretinal electric field between the stimulating electrode unit  12  and the ground return electrode unit  16  as the electric field traverses through the neuroretina  50 . A non-skewed electrical field that is perpendicular to the neuroretina vitreous-facing surface efficiently stimulates remaining neuroretinal cells. For reference purposes, other items and structures of the eye that are shown are the cornea  58 , iris  62 , lens  60 , sclera  64 , optic nerve  66  and the incident light images  56 . 
       FIG. 7  shows a cross-sectional view of another embodiment of the retinal device  10   c  including the preferred embodiment retinal device  10  as described in  FIGS. 1A and 1B  and other features. The stimulating electrode unit  12  is disposed in the subretinal space between the neuroretina  50  and the retinal pigment epithelium  52 , and the ground return electrode unit  16  is disposed in the vitreous cavity  54 , including a tail extension  30   a  that has a generally looped ground electrode. Although the stimulating electrode unit  12  is preferably positioned in the subretinal space with the ground return electrode unit  16  positioned in the vitreous cavity, in other embodiments the positioning of the stimulating electrode unit  12  and ground electrode unit  16  may be reversed. 
     A purpose of the loop electrode of the tail extension  30   a  is to electrically extend the location of the ground return electrode further into the vitreous cavity  54  and in an even manner. An evenly disposed ground electrode in the vitreous cavity relative to the subretinal stimulating electrode array aids the maintenance of a tranretinal stimulating electrical field in a perpendicular direction relative to the neuroretinal surface. Such an alignment of the electrical field relative to the neuroretinal surface efficiently stimulates the neuroretina, as compared to, for example, a transretinal electrical field that is skewed to the neuroretinal surface. For purposes of reference, other items and structures of the eye that are shown are the cornea  58 , iris  62 , lens  60 , sclera  64 , optic nerve  66  and the incident light images  56 . 
       FIG. 8  shows a cross-sectional view of yet another embodiment retinal device  10   d  including the preferred embodiment retinal device  10  as described in  FIGS. 1A and 1B , including an attached tail extension  30   b . The tail extension electrically connects with at least one bias photodiode  30   c  disposed in the lens capsule  60   b  of the eye  6 , the bias photodiode  30   c  containing the extended location of the ground return electrode  32   b . The bias photodiode  30   c  provides additional voltage and/or current to the electrode stimulating unit  12  in the subretinal space. Additional stimulating voltage and the resulting current may be required to stimulate more severely damaged retinas compared to less severely damage retinas. The bias photodiode, which may also be a series of photodiodes  30   c  are electrically connected together in a series or parallel configuration, as is known in the art, to provide the increased voltage and/or current. For purposes of reference, other items and structures of the eye  6  that are shown are the cornea  58 , iris  62 , sclera  64 , neuroretina  50 , retinal pigment epithelium  52 , optic nerve  66 , and the incident light images  56 . 
       FIG. 9  shows a cross-sectional view of yet another embodiment retinal device  10   e  including the preferred embodiment retinal device  10  as described in  FIGS. 1A and 1B , and an attached tail extension  30   d  that electrically connects with at least one bias photodiode  30   e  preferably disposed in front of the iris  62  of the eye  6 . The placement of at least one bias photodiode in this location allows all of the bias photodiode to be exposed to light, compared to a bias photodiode disposed behind the iris. The bias photodiode  30   e  contains the extended location of the ground return electrode  32   c , and the bias photodiode or photodiodes  30   e  to provide additional voltage and/or current to the electrode stimulating unit  12  in the subretinal space. The bias photodiode or photodiodes  30   e  are electrically connected together in a series or parallel configuration to provide increased voltage and/or current, as is known in the art. For reference purposes, other items and structures of the eye  6  that are shown are the cornea  58 , lens  60 , sclera  64 , neuroretina  50 , retinal pigment epithelium  52  and optic nerve  66 , and the incident light images  56 . 
     It is to be understood that changes and modifications to the embodiments described above will be apparent to those skilled in the art, and are contemplated. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention.