fig1 is a schematic view of a 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 the horizontal in the visual field , implanted epiretinally , which covers about 10 × 20 degrees of visual angle . fig2 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 fig6 and 7 . turning to fig2 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 fig4 ) adapted to be used together and communicate with an internal rf coil ( later shown in fig6 and 7 ). the mounting system 5 also encloses the rf circuitry 17 ( see fig4 ) for modulating , demodulating , transmitting , and receiving an rf signal . external coil arrangement 4 and mounting system 5 are connected by a flexible connector 6 . fig4 shows an exploded view of the external coil arrangement 4 and mounting system 5 . as also shown in fig2 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 fig4 include : wires 15 connecting pcbs 11 and 12 ; a mounting bracket 16 ( later described in fig5 ); 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 fig1 ), 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 fig8 a , 8 b and 9 . fig1 shows an arrangement comprising a visor 1 connected to a visual processing unit 35 through a cable 36 . 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 , fig6 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 . 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 fig4 . with the external coil 4 , 13 angled toward the face ( e . g ., at 25 degrees ) ( see fig2 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 . 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 . in particular , reference can be made to fig5 , which shows a further perspective view of the apparatus shown in fig2 and 3 . in particular , fig5 shows a sliding bar mechanism 19 which is tightened into position by screws 20 . fig5 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 . 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 . fig6 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 257 which can pierce the sclera and be electrically coupled to an electronics package 26 external to the sclera . electronic package 26 includes the rf receiver and electrode drivers . 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 . 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 . fig7 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 . 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 .
the present invention is a visor for retinal stimulation of visually impaired subjects . 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 .