Abstract:
A visor for retinal stimulation of visually impaired subjects is shown. The visor comprises a frame, an external coil, a camera and a mounting system. A connector allows the external coil to be positioned along a first direction. A sliding device allows the external coil to be positioned along a second direction. Positioning of the visor on a subject&#39;s nose allows the external coil to be positioned along a third direction. Positioning of the external coil along the first, second or third direction is useful to maximize coupling RF coupling between the external coil and an internal coil implanted on a subject wearing the visor.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Ser. No. 60/876,645 for “Visor for a Visual Prosthesis” filed on Dec. 22, 2006 and to PCT application No. PCT/US2007/013918 (applicant&#39;s docket number S416-PCT) for “Apparatus and Method for Electrical Stimulation of Human Retina” filed on Jun. 15, 2007, both of which are incorporated herein by reference in their entirety. 
     
    
     GOVERNMENT RIGHTS NOTICE 
       [0002]    This invention was made with government support under grant No. R24EY12893-01, awarded by the National Institutes of Health. The government has certain rights in the invention. 
     
    
     FIELD 
       [0003]    The present disclosure is generally directed to neural stimulation and more specifically to a visual prosthetic apparatus for retinal stimulation. 
       BACKGROUND 
       [0004]    As intraocular surgical techniques have advanced, it has become possible to apply stimulation on small groups and even on individual retinal cells to generate focused phosphenes through devices implanted within the eye itself. This has sparked renewed interest in developing methods and apparatuses 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. 
         [0005]    Neural tissue can be artificially stimulated and activated by prosthetic devices that pass pulses of electrical current through electrodes on such a device. The passage of current causes changes in electrical potentials across visual neuronal membranes, which can initiate visual neuron action potentials, which are the means of information transfer in the nervous system. 
         [0006]    Based on this mechanism, it is possible to input information into the nervous system by coding the information as a sequence of electrical pulses which are relayed to the nervous system via the prosthetic device. In this way, it is possible to provide artificial sensations including vision. 
         [0007]    One typical application of neural tissue stimulation is in the rehabilitation of the blind. Some forms of blindness involve selective loss of the light sensitive transducers of the retina. Other retinal neurons remain viable, however, and may be activated in the manner described above by placement of a prosthetic electrode device on the inner (toward the vitreous) retinal surface (epiretinal). This placement must be mechanically stable, minimize the distance between the device electrodes and the visual neurons, and avoid undue compression of the visual neurons. 
         [0008]    In 1986, Bullara (U.S. Pat. No. 4,573,481) 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. 
         [0009]    Dawson and Radtke stimulated cat&#39;s retina by direct electrical stimulation of the retinal ganglion cell layer. These experimenters placed nine and then fourteen electrodes upon the inner retinal layer (i.e., primarily the ganglion cell layer) of two cats. Their experiments suggested that electrical stimulation of the retina with 30 to 100 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 U.S. Pat. No. 4,628,933 to Michelson). 
         [0010]    The Michelson &#39;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. U.S. Pat. No. 4,837,049 to Byers describes spike electrodes for neural stimulation. Each spike electrode pierces neural tissue for better electrical contact. U.S. Pat. No. 5,215,088 to Norman describes an array of spike electrodes for cortical stimulation. Each spike pierces cortical tissue for better electrical contact. 
         [0011]    The 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., de Juan, et al., 99 Am. J. Ophthalmol. 272 (1985). These retinal tacks have proved to be biocompatible and remain embedded in the retina, with the 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 array to the retina. U.S. Pat. No. 5,109,844 to de Juan describes a flat electrode array placed against the retina for visual stimulation. U.S. Pat. No. 5,935,155 to Humayun describes a retinal prosthesis for use with the flat retinal array described in de Juan. 
       SUMMARY 
       [0012]    According to a first embodiment of the present disclosure, a visual prosthetic apparatus for retinal stimulation is disclosed, comprising: an implantable portion and an external portion, wherein the implantable portion comprises an RF receiver, an internal coil, and an array of electrodes, wherein the external portion comprises a frame, a camera mounted on the frame and an external coil mounted on the frame, and wherein distance between the internal coil and the external coil is controllable along at least one of a medial-lateral direction, anterior-posterior direction and a superior-inferior direction. 
         [0013]    According to a second embodiment of the present disclosure, a visor for visually impaired subjects is disclosed, comprising: a frame; a coil arrangement including an external coil; a camera; a mounting system to mount the coil arrangement on the frame; a connection between the camera and the mounting system; a flexible connector connecting the coil arrangement with the mounting system, the flexible connector being adapted to adjust positioning of the external coil along a first direction; a sliding device positioned between the frame and the mounting system, the sliding device being adapted to adjust positioning of the external coil along a second direction; and a structure attached to the frame, the structure allowing positioning of the visor on a subject&#39;s nose, wherein movement of the visor on the subject&#39;s nose allows positioning of the external coil along a third direction. 
         [0014]    Further embodiments are disclosed throughout the specification, drawings and claims of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a brief schematic view of an implanted visual prosthesis. 
           [0016]      FIGS. 2 and 3  show perspective views of an external portion of a visual prosthetic apparatus. 
           [0017]      FIG. 4  is an exploded view of the external coil arrangement and mounting system shown in  FIGS. 2 and 3 . 
           [0018]      FIG. 5  is a further perspective view of the external portion of the visual prosthetic apparatus. 
           [0019]      FIG. 6  shows a perspective view of the implantable portion of the visual prosthesis. 
           [0020]      FIG. 7  is a side view of the implantable portion of the visual prosthesis. 
           [0021]      FIGS. 8A and 8B  (to be viewed side by side) show a circuital diagram of RF circuitry  17  shown in  FIG. 4 . 
           [0022]      FIG. 9  shows a table with exemplary values for the components of the circuit of  FIGS. 8A and 8B . 
           [0023]      FIG. 10  shows an arrangement comprising a visor, a visual processing unit and a cable connecting the visor to the visual processing unit. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]      FIG. 1  is a schematic view of prosthesis for stimulating retinal cells. Patients suffering from retinitis pigmentosa (RP) sustain severe vision loss as a result of photoreceptor death. In the preferred prosthesis, the electrode array is aligned in a 6×10 matrix with the wider dimension oriented to horizontal in the visual field, implanted epiretinally, which covers about 10×20 degrees of visual angle. The upper sub figure shows a schematic of an electrode array in a 6×10 configuration. The subfigure from this schematic details a graphic representation of the system of neural cells under each electrode, wherein the neural cells shown are no longer organized, but unorganized with significant cell death. 
         [0025]      FIGS. 2 and 3  show two different perspective views of an external portion of a visual prosthetic apparatus according to the present disclosure. ‘External’ is here meant to indicate that the portion is external to the human body, and not implanted therein. External portion  1  is adapted to be used in combination with an implantable portion  23 , shown in  FIGS. 6 and 7 . Turning to  FIGS. 2 and 3 , the external portion  1  comprises a frame  2  holding a camera  3 , an external coil arrangement  4  and a mounting system  5  for the external coil arrangement  4 . The external coil arrangement  4  comprises external transmitting and receiving radio-frequency (RF) coils (later shown in  FIG. 4 ) adapted to be used together and communicate with an internal RF coil (later shown in  FIGS. 6 and 7 ). The mounting system  5  also encloses the RF circuitry  17  (see  FIG. 4 ) for modulating, demodulating, transmitting, and receiving an RF signal. External coil arrangement  4  and mounting system  5  are connected by a flexible connector  6 . 
         [0026]      FIG. 4  shows an exploded view of the external coil arrangement  4  and mounting system  5 . As also shown in  FIGS. 2 and 3 , the external coil arrangement  4  and mounting system  5  are connected by a flexible connector  6 . In particular, the flexible connector  6  is attached to RF coil enclosure halves  7  and  8  on the coil side and to enclosure case halves  9  and  10  on the mounting system side. The external coil arrangement  4  comprises coil enclosure halves  7  and  8 , enclosing printed circuit boards (PCB)  11  and  12  surrounding an RF transmitting coil  13 . The PCBs  11  and  12  further include telemetry receiving coils. The mounting system  5  comprises case halves  9  and  10  enclosing an RF visor cable assembly  14 . Other mechanical components shown in  FIG. 4  include: wires  15  connecting PCBs  11  and  12 ; a mounting bracket  16  (later described in  FIG. 5 ); and RF circuitry  17  located between case halves  9  and  10 . While video image processing is done in a remote video processing unit (shown in  FIG. 10 ), the RF circuitry  17  is incorporated into the mounting system  5  to reduce losses in the cable connecting the video processing unit to the glasses. PCBs  11  and  12  can be made of glass base epoxy and laminated with copper. An exemplary circuital diagram of RF circuitry  17  is shown in  FIGS. 8A ,  8 B and  9 .  FIG. 10  shows an arrangement comprising a visor  1  connected to a visual processing unit  35  through a cable  36 . 
         [0027]    Three structural features are provided in the visual prosthesis to control the distance, and thereby reduce the distance, between the external coil  13  (included in arrangement  14 ) and the inductive (implanted) coil ( 27 ,  FIGS. 6 and 7 ). The three structural features correspond to movement of the external coil along the three possible spatial axes occupied by the two coils. That is, the external and inductive coils can be viewed as being separated in anatomical axes: the medial-lateral, superior-inferior, and the anterior-posterior axis. Control of the distance between external coil  13  and implanted coil  27  is important, because it allows a better signal transmission via the  13 - 27  inductive coupling. 
         [0028]    The first structural feature is adapted to reduce the distance between the coils along the medial-lateral axis by bending the external coil arrangement  4 , thus bending the external coil  13 . The distance in this medial-lateral axis should be equivalent to the separation distance of the coils if the centers of the coils are aligned. The enclosure  4  of the external coil  13  is attached to the mounting system  5 , which is attached to the leg frame  2  of the visual apparatus. While the RF circuitry within the mounting system  5  is in line with the leg frame  2 , the external coil  13  has been given a preferential bend  18  towards the face using the flexible connector  6  shown in  FIG. 4 . With the external coil  4 ,  13  angled toward the face (e.g., at 25 degrees) (see  FIGS. 2 and 3 ) , the external coil  4 ,  13  makes contact with the subject&#39;s face and the flexible connector allows conformation to the subject&#39;s facial contours. Thus, the external coil  4 ,  13  is brought in as close as possible in the medial-lateral axis for the subject. 
         [0029]    The second structural feature is a sliding bar mechanism adapted to control movement of the external coil  4 ,  13  along the anterior-posterior axis. The point at which the mounting system  5  connects to the visor allows for adjustment along this anterior-posterior axis (e.g., a 7 mm adjustment). The sliding bar mechanism can be fixed in place when the optimal position is found by tightening two screws on the sides of the sliding bar. 
         [0030]    In particular, reference can be made to  FIG. 5 , which shows a further perspective view of the apparatus shown in  FIGS. 2 and 3 . In particular,  FIG. 5  shows a sliding bar mechanism  19  which is tightened into position by screws  20 .  FIG. 5  also shows a trench  21  for routing camera cable connected to the camera  3 . The camera cable end can be inserted into hole  22  of the mounting system  5 . 
         [0031]    The third structural feature is adjustment of the position of the external coil  4 ,  13  along the superior-inferior axis by varying the placement of the visual apparatus  1  along the subject&#39;s nose. When the visual apparatus  1  is worn close to the face, the external coil  13  is higher, and when worn further from the face, the external coil  13  is lower. Using these three structural adjustments alone or in combination, the coil separation distance can be adjusted to obtain an optimal RF link for individual subjects. 
         [0032]      FIG. 6  shows a perspective view of an implantable portion  23  of a retinal prosthesis as disclosed. An electrode array  24  is mounted by a retinal tack or similar means to the epiretinal surface. The electrode array  24  is electrically coupled by a cable  25 , which can pierce the sciera and be electrically coupled to an electronics package  26  external to the sclera. Electronic package  26  includes the RF receiver and electrode drivers. 
         [0033]    The electronics package  26  can be electrically coupled to the secondary inductive coil  27 . In one aspect, the secondary inductive coil  27  is made from wound wire. Alternatively, the secondary inductive coil may be made from a thin film polymer sandwich with wire traces deposited between layers of thin film polymer. The electronics package  26  and secondary inductive coil  27  are held together by a molded body  28 . The molded body  28  may also include suture tabs  29 . The molded body narrows to form a strap  30  which surrounds the sclera and holds the molded body  28 , secondary inductive coil  27 , and electronics package  26  in place. The molded body  28 , suture tabs  29  and strap  30  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. Furthermore, silicone remains flexible enough to accommodate implantation and to adapt to variations in the curvature of an individual sclera. In one aspect, the secondary inductive coil  27  and molded body  28  are oval shaped, and in this way, a strap  30  can better support the oval shaped coil. 
         [0034]    The entire implantable portion  23  is attached to and supported by the sclera of a subject. The eye moves constantly. The eye moves to scan a scene and also has a jitter motion to prevent image stabilization. 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. 
         [0035]      FIG. 7  shows a side view of the implantable portion of the retinal prosthesis, in particular, emphasizing the fan tail  31 . When the retinal prosthesis is implanted, the strap  30  has to be passed under the eye muscles to surround the sclera. The secondary inductive coil  27  and molded body  28  should also follow the strap under the lateral rectus muscle on the side of the sclera. The implantable portion  23  of the retinal prosthesis is very delicate. It is easy to tear the molded body  28  or break wires in the secondary inductive coil  27 . In order to allow the molded body  28  to slide smoothly under the lateral rectus muscle, the molded body is shaped in the form of a fan tail  31  on the end opposite the electronics package  26 . Element  32  shows a retention sleeve, while elements  33  and  34  show holes for surgical positioning and a ramp for surgical positioning, respectively. 
         [0036]    In summary, a visual prosthetic apparatus is provided. The apparatus provides a means for adjusting the RF link to the internal coils. While the invention has been described by means of specific embodiments and applications thereof, it is understood that numerous modifications and variations could be made thereto by those skilled in the art without departing from the spirit and scope of the invention. It is therefore to be understood that within the scope of the claims, the invention may be practiced otherwise than as specifically described herein.