Abstract:
The present invention is generally directed to visual neural stimulation and more specifically to improved usability of a visual prosthesis, and a visual prosthesis structure easily adaptable to the eye or the brain. They system includes a pattern recognition component, and zoom component combined with an indication component for indicating the location of the pattern, such as a face, in a zoomed out image.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claim priority to, benefit of, and incorporates by reference, U.S. Provisional Application 62/036,463, filed Aug. 12, 2014 for Visual Prosthesis. 
    
    
     FIELD OF THE INVENTION 
     The present invention is generally directed to improved usability of a visual prosthesis, and more specifically to pattern detection for a visual prosthesis. 
     BACKGROUND OF THE INVENTION 
     Detection and Tacking of Faces in Real Environments by R. Herpers et. al. from International Workshop on Recognition, Analysis and Tracking of Faces and Gestures in Real-Time Systems, 1999, IEEE Proceedings describes basics of facial detection and recognition software for general applications. 
     Xuming He presented an ARVO poster in 2011 describing a system for a visual prosthesis that automatically zooms in on a face in a visual scene to help a visual prosthesis user identify the face. 
     U.S. Patent Application 20080058894 for Audio-tactile Vision Substitution System to Dewhurst describes providing visual information to a vision impaired person using audio or tactile information including information regarding facial characteristics. 
     International patent application WO 20010384465 for Object Tracking for Artificial Vision by Barns et al. describes a system for tracking objects, such as a face for a visually impaired user. 
     US Patent application 20130035742 for Face Detection Tracking and Recognition for a Visual Prosthesis, the disclosure of which is incorporated herein by reference, is by the present applicants and describes a system for identifying a face and indicating is location to the user of a visual prosthesis. 
     SUMMARY OF THE INVENTION 
     The present invention is generally directed to visual neural stimulation and more specifically to improved usability of a visual prosthesis, and a visual prosthesis structure easily adaptable to the eye or the brain. They system includes a pattern detection and recognition component, and zoom component combined with an indication component for indicating the location of the pattern, such as a face, in a zoomed out image. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is an photograph of an electrode array on a retina showing the 20 degree field of view covered by the electrode array. 
         FIG. 1B  is an experimental face detection setup as seen through the camera of a visual prosthesis with a 53 degree field of view. 
         FIG. 2A  is an experimental face detection setup as seen through the camera of a visual prosthesis, showing the narrower field of view to the electrode array, and the electrodes stimulated by a face detection filter. 
         FIG. 2B  is an experimental face detection setup as seen through the camera of a visual prosthesis, showing the wider field of view of the camera mapped to the electrode array, and the electrodes stimulated by a face detection filter. 
         FIG. 3  is a flowchart showing facial detection. 
         FIG. 4  is a set of three flowcharts equating face detection response to square localization. 
         FIG. 5  is a flowchart showing the process of face detection and recognition. 
         FIG. 6  is a flowchart showing the process of face cueing. 
         FIG. 7  is a perspective view of the implanted portion of the preferred visual prosthesis. 
         FIG. 8  is a side view of the implanted portion of the preferred visual prosthesis showing the strap fan tail in more detail. 
         FIG. 9  shows the components of a visual prosthesis fitting system. 
         FIG. 10 a    shows a LOSS OF SYNC mode. 
         FIG. 10 b    shows an exemplary block diagram of the steps taken when VPU does not receive back telemetry from the Retinal stimulation system. 
         FIG. 10 c    shows an exemplary block diagram of the steps taken when the subject is not wearing Glasses. 
         FIGS. 11-1, 11-2, 11-3 and 11-4  show an exemplary embodiment of a video processing unit.  FIG. 11-1  should be viewed at the left of  FIG. 11-2 .  FIG. 11-3  should be viewed at the left of  FIG. 11-4 .  FIGS. 11-1 and 11-2  should be viewed on top of  FIGS. 11-3 and 11-4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the claims. 
     An aspect of the invention is a method of aiding a visual prosthesis subject including detecting a face in the subject&#39;s visual scene and communicating the location of the detected face including zooming out to show the location of the detected face through a highlight; and providing cues to the subject regarding a detected face. The cue may include sound, vibration, stating a name associated with the detected face, highlighting the detected face, zooming in on the detected face, or tactile feedback. The method may further include looking up the detected face in a look up table to provide a name associated with the detected face. The cue may further include an indication of if the face is looking toward the subject, to the side or looking away. A further aspect of the invention is including information about a facial characteristic in the cue. Facial characteristics may include gender, size, distance, head movement, or other body motion. All of these characteristics are controllable by the subject through controls on the video processing unit worn on the body. 
     Referring to  FIG. 1 , The currently available visual prosthesis provides an electrode array  10  which stimulates the retina to provide a field of view of 20 degrees ( FIG. 1A ) while a camera  12  provides a 53 degree field of view ( FIG. 1B ). While larger arrays are desirable and will be available in the future, it is clear that camera technology will always surpass electrode array technology. Zoom system have been provided in visual prostheses. A one to one ratio is best for locomotion and hand eye coordination as described in US-2008-0183244-A1, Field of View Matching in a Visual Prosthesis. It is also known that zoom in can be beneficial for task such as reading. However, the facial detection task benefits from a wider angle view. It is often beneficial for a visual prosthesis user know the location of faces within a scene. Those faces can be identified with a simple highlight or only stimulating the location of the face. It such a case a wider field of view supports finding faces quickly. It should be clear that while described in relation to facial detection any pattern of interest can be detected and it location identified by the same method. Patterns of interest may include, for example, stumble or trip hazards, automobiles, doors, windows or faces. 
     It is not necessary to zoom the subject&#39;s view to detect and identify such patterns. In this example, the camera views 53 degrees while only 20 degrees is presented to the subjection through an electrode array. Software can be constantly scanning the 53 degree image and notifying the user when a pattern of interest is detected in the scene. When a pattern of interest is detected, the system can zoom out and cue a user, or cue a user and wait for the user to zoom out manually. It is important to not change the field of view without the user&#39;s knowledge. 
     This function can be further combined with recognition functions such as looking up the a detected face and speaking the name associated with the face. Alternatively the system can describe characteristics of the face. 
     Referring to  FIG. 2 , the experimental face detection setup is shown as seen through the camera of a visual prosthesis, showing the narrower field of view  2000  to the electrode array  10 . A face is detected  2002  and electrodes stimulated by a face detection filter  2004 . The additional information provided by the face detection filter is minimal. A visual prosthesis user will need to scan the scene through the 20 degree view until a face is detected. At this level the visual prosthesis user would probably be able to detect a face without the filter. 
     Referring to  FIG. 2B , the experimental face detection setup is shown as seen through the camera of a visual prosthesis. In this case the wider field of view of the camera  12  is mapped to the electrode array  10 . A face is detected  2006  by a face detection filter and electrodes are stimulated  2008 . With the wider field of view, the visual prosthesis user is able to identify the location of a face within the scene with minimal or no scanning. Preferably a visual prosthesis user would be able to switch modes quickly and easily. For example, a single button could be provided on the VPU which shifts to the wider field of view and activating the face detection software. Releasing the button would return the visual prosthesis to the previous mode. This allows the user, when entering a room for example, to quickly indentify the location of faces in the room. 
     While described in terms of face detection, the present invention, in particular as it applies to wide field of view is also applicable to wide range of other uses, such as hazard detection. Any item that can be detected by the visual prosthesis camera and image processing software can be readily identified with the present invention. As another example, when combined with an infrared camera, heat sources can be identified. 
     The following table shows face detection response times in a clinical trial 
                                     Patient ID   Wide FOV (53 deg.)   Normal FOV (20 deg.)                   1   38 ± 4    53 ± 12       2   20 ± 2   42 ± 5       3    5 ± 1   11 ± 3       4   12 ± 2   22 ± 4                    
The times are in seconds based on 10 trials for each subject after 10 practice trials. Another trial was conducted with and without a target (target turned away not showing their face.
 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 Patient ID 
                 Mean Response Time 
               
               
                   
                   
               
             
             
               
                   
                 1 
                 5.2 ± .9 
               
               
                   
                 2 
                 6.4 ± .7 
               
               
                   
                   
               
             
          
         
       
     
     Referring to  FIG. 3 , simple face tracking can be a significant benefit to a blind person. The presence of multiple faces may be also relayed. The process flow of basic face detection and tracking is provided. The video processor records a visual scene  102 , show here with two faces. The video processor draws a square around a detected face  104 . The video processor draws squares around both face units and draws a smaller square around the identifiable portions of the two faces for recognition processing  106 . Even with a very low resolution electrode array, it is possible for a subject to locate the faces  108 , to improve interaction with the other people. 
     Referring to  FIG. 4 , square localization is a common task preformed by visual prosthesis patients. See US Patent Application 2010/0249878, for Visual Prosthesis Fitting Training and Assessment System and Method, filed Mar. 26, 2010 which is incorporated herein by reference. Providing a square over a detected face, simplifies the face tracking to the level of a square localization. In the first example  110 , the face is indentified at an angle. It may be advantageous to straighten the square to improve user recognition. In the second example  112  the face is outside the visual scene so no highlight is provided. In the third example  114 , the face square is simply highlighted without modification. The distance to the person, distance direction and velocity may also be relayed to the patient. 
     Referring to  FIG. 5 , the process of face detection begins by scanning the input image from the camera for a pattern of face  202 . There are many well known processes for indentifying faces in an image. If a face is detected, it is compared to a database of known faces  204 . If the face is unknown, the face is cued  208  as described in greater detail in  FIG. 6 . If the face is known, it is announced  206 . Finally facial characteristics are determined  210 . 
     Referring to  FIG. 6 , there are several options for cueing the presence of an unknown face which are selectable by the user. The user can change the selection by activating controls on the VPU  20 . The system determines if face highlighting is selected  302 , and highlights the face  304 . In a low resolution visual prosthesis this can be accomplished simply replacing the face with a bright image. In a higher resolution visual prosthesis this may be accomplished by marking a square or circle around the face. Alternatively if Zoom is selected  306 , the visual prosthesis zooms in on the face aiding the user in indentifying the face  308 , or zooming out to provide the location of the face. If vibration is selected  310  the visual processing unit vibrates (like a cell phone in silent mode)  312 . If tone is selected  314 , the speaker on the visual prosthesis emits a tone  316 . Note that the cues may be used in combination such as highlight, vibrate and tone. 
       FIGS. 7 and 8  present the general structure of a visual prosthesis used in implementing the invention. 
       FIG. 7  shows a perspective view of the implanted portion of the preferred visual prosthesis. A flexible circuit  1  includes a flexible circuit electrode array  10  which is mounted by a retinal tack (not shown) or similar means to the epiretinal surface. The flexible circuit electrode array  10  is electrically coupled by a flexible circuit cable  12 , which pierces the sclera and is electrically coupled to an electronics package  14 , external to the sclera. 
     The electronics package  14  is electrically coupled to a secondary inductive coil  16 . Preferably the secondary inductive coil  16  is made from wound wire. Alternatively, the secondary inductive coil  16  may be made from a flexible circuit polymer sandwich with wire traces deposited between layers of flexible circuit polymer. The secondary inductive coil receives power and data from a primary inductive coil  17 , which is external to the body. The electronics package  14  and secondary inductive coil  16  are held together by the molded body  18 . The molded body  18  holds the electronics package  14  and secondary inductive coil  16  end to end. The secondary inductive coil  16  is placed around the electronics package  14  in the molded body  18 . The molded body  18  holds the secondary inductive coil  16  and electronics package  14  in the end to end orientation and minimizes the thickness or height above the sclera of the entire device. The molded body  18  may also include suture tabs  20 . The molded body  18  narrows to form a strap  22  which surrounds the sclera and holds the molded body  18 , secondary inductive coil  16 , and electronics package  14  in place. The molded body  18 , suture tabs  20  and strap  22  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. However, silicone remains flexible enough to accommodate implantation and to adapt to variations in the curvature of an individual sclera. The secondary inductive coil  16  and molded body  18  are preferably oval shaped. A strap  22  can better support an oval shaped coil. It should be noted that the entire implant is attached to and supported by the sclera. An eye moves constantly. The eye moves to scan a scene and also has a jitter motion to improve acuity. 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. 
       FIG. 8  shows a side view of the implanted portion of the visual prosthesis, in particular, emphasizing the fan tail  24 . When implanting the visual prosthesis, it is necessary to pass the strap  22  under the eye muscles to surround the sclera. The secondary inductive coil  16  and molded body  18  must also follow the strap  22  under the lateral rectus muscle on the side of the sclera. The implanted portion of the visual prosthesis is very delicate. It is easy to tear the molded body  18  or break wires in the secondary inductive coil  16 . In order to allow the molded body  18  to slide smoothly under the lateral rectus muscle, the molded body  18  is shaped in the form of a fan tail  24  on the end opposite the electronics package  14 . The strap  22  further includes a hook  28  the aids the surgeon in passing the strap under the rectus muscles. 
     Referring to  FIG. 9 , a Fitting System (FS) may be used to configure and optimize the visual prosthesis ( 3 ) of the Retinal Stimulation System ( 1 ). 
     The Fitting System may comprise custom software with a graphical user interface (GUI) running on a dedicated laptop computer ( 10 ). Within the Fitting System are modules for performing diagnostic checks of the implant, loading and executing video configuration files, viewing electrode voltage waveforms, and aiding in conducting psychophysical experiments. A video module can be used to download a video configuration file to a Video Processing Unit (VPU) ( 20 ) and store it in non-volatile memory to control various aspects of video configuration, e.g. the spatial relationship between the video input and the electrodes. The software can also load a previously used video configuration file from the VPU ( 20 ) for adjustment. 
     The Fitting System can be connected to the Psychophysical Test System (PTS), located for example on a dedicated laptop ( 30 ), in order to run psychophysical experiments. In psychophysics mode, the Fitting System enables individual electrode control, permitting clinicians to construct test stimuli with control over current amplitude, pulse-width, and frequency of the stimulation. In addition, the psychophysics module allows the clinician to record subject responses. The PTS may include a collection of standard psychophysics experiments developed using for example MATLAB (MathWorks) software and other tools to allow the clinicians to develop customized psychophysics experiment scripts. 
     Any time stimulation is sent to the VPU ( 20 ), the stimulation parameters are checked to ensure that maximum charge per phase limits, charge balance, and power limitations are met before the test stimuli are sent to the VPU ( 20 ) to make certain that stimulation is safe. 
     Using the psychophysics module, important perceptual parameters such as perceptual threshold, maximum comfort level, and spatial location of percepts may be reliably measured. 
     Based on these perceptual parameters, the fitting software enables custom configuration of the transformation between video image and spatio-temporal electrode stimulation parameters in an effort to optimize the effectiveness of the visual prosthesis for each subject. 
     The Fitting System laptop ( 10 ) is connected to the VPU ( 20 ) using an optically isolated serial connection adapter ( 40 ). Because it is optically isolated, the serial connection adapter ( 40 ) assures that no electric leakage current can flow from the Fitting System laptop ( 10 ). 
     As shown in  FIG. 9 , the following components may be used with the Fitting System according to the present disclosure. A Video Processing Unit (VPU) ( 20 ) for the subject being tested, a Charged Battery ( 25 ) for VPU ( 20 ), Glasses ( 5 ), a Fitting System (FS) Laptop ( 10 ), a Psychophysical Test System (PTS) Laptop ( 30 ), a PTS CD (not shown), a Communication Adapter (CA) ( 40 ), a USB Drive (Security) (not shown), a USB Drive (Transfer) (not shown), a USB Drive (Video Settings) (not shown), a Patient Input Device (RF Tablet) ( 50 ), a further Patient Input Device (Jog Dial) ( 55 ), Glasses Cable ( 15 ), CA-VPU Cable ( 70 ), CFS-CA Cable ( 45 ), CFS-PTS Cable ( 46 ), Four (4) Port USB Hub ( 47 ), Mouse ( 60 ), LED Test Array ( 80 ), Archival USB Drive ( 49 ), an Isolation Transformer (not shown), adapter cables (not shown), and an External Monitor (not shown). 
     The external components of the Fitting System according to the present disclosure may be configured as follows. The battery ( 25 ) is connected with the VPU ( 20 ). The PTS Laptop ( 30 ) is connected to FS Laptop ( 10 ) using the CFS-PTS Cable ( 46 ). The PTS Laptop ( 30 ) and FS Laptop ( 10 ) are plugged into the Isolation Transformer (not shown) using the Adapter Cables (not shown). The Isolation Transformer is plugged into the wall outlet. The four (4) Port USB Hub ( 47 ) is connected to the FS laptop ( 10 ) at the USB port. The mouse ( 60 ) and the two Patient Input Devices ( 50 ) and ( 55 ) are connected to four (4) Port USB Hubs ( 47 ). The FS laptop ( 10 ) is connected to the Communication Adapter (CA) ( 40 ) using the CFS-CA Cable ( 45 ). The CA ( 40 ) is connected to the VPU ( 20 ) using the CA-VPU Cable ( 70 ). The Glasses ( 5 ) are connected to the VPU ( 20 ) using the Glasses Cable ( 15 ). 
     Stand-Alone Mode 
     Referring to  FIG. 10 , in the stand-alone mode, the video camera  13 , on the glasses  5 , captures a video image that is sent to the VPU  20 . The VPU  20  processes the image from the camera  13  and transforms it into electrical stimulation patterns that are transmitted to the external coil  17 . The external coil  17  sends the electrical stimulation patterns and power via radio-frequency (RF) telemetry to the implanted retinal stimulation system. The internal coil  16  of the retinal stimulation system receives the RF commands from the external coil  17  and transmits them to the electronics package  14  that in turn delivers stimulation to the retina via the electrode array  10 . Additionally, the retinal stimulation system may communicate safety and operational status back to the VPU  20  by transmitting RF telemetry from the internal coil  16  to the external coil  17 . The visual prosthesis apparatus may be configured to electrically activate the retinal stimulation system only when it is powered by the VPU  20  through the external coil  17 . The stand-alone mode may be used for clinical testing and/or at-home use by the subject. 
     Communication Mode 
     The communication mode may be used for diagnostic testing, psychophysical testing, patient fitting and downloading of stimulation settings to the VPU  20  before transmitting data from the VPU  20  to the retinal stimulation system as is done for example in the stand-alone mode described above. Referring to  FIG. 9 , in the communication mode, the VPU  20  is connected to the Fitting System laptop  21  using cables  70 ,  45  and the optically isolated serial connection adapter  40 . In this mode, laptop  21  generated stimuli may be presented to the subject and programming parameters may be adjusted and downloaded to the VPU  20 . The Psychophysical Test System (PTS) laptop  30  connected to the Fitting System laptop  21  may also be utilized to perform more sophisticated testing and analysis as fully described in the related application U.S. Pat. No. 8,271,091, (Applicant&#39;s Docket No. S401-USA) which is incorporated herein by reference in its entirety. 
     In one embodiment, the functionality of the retinal stimulation system can also be tested pre-operatively and intra-operatively (i.e. before operation and during operation) by using an external coil  17 , without the glasses  5 , placed in close proximity to the retinal stimulation system. The coil  17  may communicate the status of the retinal stimulation system to the VPU  20  that is connected to the Fitting System laptop  21  as shown in  FIG. 9 . 
     As discussed above, the VPU  20  processes the image from the camera  13  and transforms the image into electrical stimulation patterns for the retinal stimulation system. Filters such as edge detection filters may be applied to the electrical stimulation patterns for example by the VPU  20  to generate, for example, a stimulation pattern based on filtered video data that the VPU  20  turns into stimulation data for the retinal stimulation system. The images may then be reduced in resolution using a downscaling filter. In one exemplary embodiment, the resolution of the image may be reduced to match the number of electrodes in the electrode array  10  of the retinal stimulation system. That is, if the electrode array has, for example, sixty electrodes, the image may be reduced to a sixty channel resolution. After the reduction in resolution, the image is mapped to stimulation intensity using for example a look-up table that has been derived from testing of individual subjects. Then, the VPU  20  transmits the stimulation parameters via forward telemetry to the retinal stimulation system in frames that may employ a cyclic redundancy check (CRC) error detection scheme. 
     In one exemplary embodiment, the VPU  20  may be configured to allow the subject/patient i) to turn the visual prosthesis apparatus on and off, ii) to manually adjust settings, and iii) to provide power and data to the retinal stimulation system. Referring again to  FIGS. 1 through 4 , the VPU  20  may comprise a case, and button  6  including power button for turning the VPU  20  on and off, setting button, zoom buttons for controlling the camera  13 , temple extensions  8  for connecting to the Glasses  5 , a connector port for connecting to the laptop  21  through the connection adapter  40 , indicator lights (not shown) on the VPU  20  or glasses  5  to give visual indication of operating status of the system, the rechargeable battery (not shown) for powering the VPU  20 , battery latch (not shown) for locking the battery in the case, digital circuit boards (not shown), and a speaker (not shown) to provide audible alerts to indicate various operational conditions of the system. Because the VPU  20  is used and operated by a person with minimal or no vision, the buttons on the VPU  20  may be differently shaped and/or have special markings to help the user identify the functionality of the button without having to look at it. 
     In one embodiment, the indicator lights may indicate that the VPU  20  is going through system start-up diagnostic testing when the one or more indicator lights are blinking fast (more then once per second) and are green in color. The indicator lights may indicate that the VPU  20  is operating normally when the one or more indicator lights are blinking once per second and are green in color. The indicator lights may indicate that the retinal stimulation system has a problem that was detected by the VPU  20  at start-up diagnostic when the one or more indicator lights are blinking for example once per five second and are green in color. The indicator lights may indicate that there is a loss of communication between the retinal stimulation system and the external coil  17  due to the movement or removal of Glasses  5  while the system is operational or if the VPU  20  detects a problem with the retinal stimulation system and shuts off power to the retinal stimulation system when the one or more indicator lights are always on and are orange color. One skilled in the art would appreciate that other colors and blinking patterns can be used to give visual indication of operating status of the system without departing from the spirit and scope of the invention. 
     In one embodiment, a single short beep from the speaker (not shown) may be used to indicate that one of the buttons  6  have been pressed. A single beep followed by two more beeps from the speaker (not shown) may be used to indicate that VPU  20  is turned off. Two beeps from the speaker (not shown) may be used to indicate that VPU  20  is starting up. Three beeps from the speaker (not shown) may be used to indicate that an error has occurred and the VPU  20  is about to shut down automatically. As would be clear to one skilled in the art, different periodic beeping may also be used to indicate a low battery voltage warning, that there is a problem with the video signal, and/or there is a loss of communication between the retinal stimulation system and the external coil  17 . One skilled in the art would appreciate that other sounds can be used to give audio indication of operating status of the system without departing from the spirit and scope of the invention. For example, the beeps may be replaced by an actual prerecorded voice indicating operating status of the system. 
     In one exemplary embodiment, the VPU  20  is in constant communication with the retinal stimulation system through forward and backward telemetry. In this document, the forward telemetry refers to transmission from VPU  20  to the retinal stimulation system and the backward telemetry refers to transmissions from the Retinal stimulation system to the VPU  20 . During the initial setup, the VPU  20  may transmit null frames (containing no stimulation information) until the VPU  20  synchronizes with the Retinal stimulation system via the back telemetry. In one embodiment, an audio alarm may be used to indicate whenever the synchronization has been lost. 
     In order to supply power and data to the Retinal stimulation system, the VPU  20  may drive the external coil  17 , for example, with a 3 MHz signal. To protect the subject, the retinal stimulation system may comprise a failure detection circuit to detect direct current leakage and to notify the VPU  20  through back telemetry so that the visual prosthesis apparatus can be shut down. 
     The forward telemetry data (transmitted for example at 122.76 kHz) may be modulated onto the exemplary 3 MHz carrier using Amplitude Shift Keying (ASK), while the back telemetry data (transmitted for example at 3.8 kHz) may be modulated using Frequency Shift Keying (FSK) with, for example, 442 kHz and 457 kHz. The theoretical bit error rates can be calculated for both the ASK and FSK scheme assuming a ratio of signal to noise (SNR). The system disclosed in the present disclosure can be reasonably expected to see bit error rates of 10-5 on forward telemetry and 10-3 on back telemetry. These errors may be caught more than 99.998% of the time by both an ASIC hardware telemetry error detection algorithm and the VPU&#39;s firmware. For the forward telemetry, this is due to the fact that a 16-bit cyclic redundancy check (CRC) is calculated for every 1024 bits sent to the ASIC within electronics package  14  of the Retinal Stimulation System. The ASIC of the Retinal Stimulation System verifies this CRC and handles corrupt data by entering a non-stimulating ‘safe’ state and reporting that a telemetry error was detected to the VPU  20  via back telemetry. During the ‘safe’ mode, the VPU  20  may attempt to return the implant to an operating state. This recovery may be on the order of milliseconds. The back telemetry words are checked for a 16-bit header and a single parity bit. For further protection against corrupt data being misread, the back telemetry is only checked for header and parity if it is recognized as properly encoded Bi-phase Mark Encoded (BPM) data. If the VPU  20  detects invalid back telemetry data, the VPU  20  immediately changes mode to a ‘safe’ mode where the Retinal Stimulation System is reset and the VPU  20  only sends non-stimulating data frames. Back telemetry errors cannot cause the VPU  20  to do anything that would be unsafe. 
     The response to errors detected in data transmitted by VPU  20  may begin at the ASIC of the Retinal Stimulation System. The Retinal Stimulation System may be constantly checking the headers and CRCs of incoming data frames. If either the header or CRC check fails, the ASIC of the Retinal Stimulation System may enter a mode called LOSS OF SYNC  950 , shown in  FIG. 10 a   . In LOSS OF SYNC mode  950 , the Retinal Stimulation System will no longer produce a stimulation output, even if commanded to do so by the VPU  20 . This cessation of stimulation occurs after the end of the stimulation frame in which the LOSS OF SYNC mode  950  is entered, thus avoiding the possibility of unbalanced pulses not completing stimulation. If the Retinal Stimulation System remains in a LOSS OF SYNC mode  950  for 1 second or more (for example, caused by successive errors in data transmitted by VPU  20 ), the ASIC of the Retinal Stimulation System disconnects the power lines to the stimulation pulse drivers. This eliminates the possibility of any leakage from the power supply in a prolonged LOSS OF SYNC mode  950 . From the LOSS OF SYNC mode  950 , the Retinal Stimulation System will not re-enter a stimulating mode until it has been properly initialized with valid data transmitted by the VPU  20 . 
     In addition, the VPU  20  may also take action when notified of the LOSS OF SYNC mode  950 . As soon as the Retinal Stimulation System enters the LOSS OF SYNC mode  950 , the Retinal Stimulation System reports this fact to the VPU  20  through back telemetry. When the VPU  20  detects that the Retinal Stimulation System is in LOSS OF SYNC mode  950 , the VPU  20  may start to send ‘safe’ data frames to the Retinal Stimulation System. ‘Safe’ data is data in which no stimulation output is programmed and the power to the stimulation drivers is also programmed to be off. The VPU  20  will not send data frames to the Retinal Stimulation System with stimulation commands until the VPU  20  first receives back telemetry from the Retinal Stimulation System indicating that the Retinal Stimulation System has exited the LOSS OF SYNC mode  950 . After several unsuccessful retries by the VPU  20  to take the implant out of LOSS OF SYNC mode  950 , the VPU  20  will enter a Low Power Mode (described below) in which the implant is only powered for a very short time. In this time, the VPU  20  checks the status of the implant. If the implant continues to report a LOSS OF SYNC mode  950 , the VPU  20  turns power off to the Retinal Stimulation System and tries again later. Since there is no possibility of the implant electronics causing damage when it is not powered, this mode is considered very safe. 
     Due to an unwanted electromagnetic interference (EMI) or electrostatic discharge (ESD) event the VPU  20  data, specifically the VPU firmware code, in RAM can potentially get corrupted and may cause the VPU  20  firmware to freeze. As a result, the VPU  20  firmware will stop resetting the hardware watchdog circuit, which may cause the system to reset. This will cause the watchdog timer to expire causing a system reset in, for example, less than 2.25 seconds. Upon recovering from the reset, the VPU  20  firmware logs the event and shuts itself down. VPU  20  will not allow system usage after this occurs once. This prevents the VPU  20  code from freezing for extended periods of time and hence reduces the probability of the VPU sending invalid data frames to the implant. 
     Supplying power to the Retinal stimulation system can be a significant portion of the VPU  20 &#39;s total power consumption. When the Retinal stimulation system is not within receiving range to receive either power or data from the VPU  20 , the power used by the VPU  20  is wasted. 
     Power delivered to the Retinal stimulation system may be dependent on the orientation of the coils  17  and  16 . The power delivered to the Retinal stimulation system may be controlled, for example, via the VPU  20  every 16.6 ms. The Retinal stimulation system may report how much power it receives and the VPU  20  may adjust the power supply voltage of the RF driver to maintain a required power level on the Retinal stimulation system. Two types of power loss may occur: 1) long term (&gt;˜1 second) and 2) short term (&lt;˜1 second). The long term power loss may be caused, for example, by a subject removing the Glasses  5 . 
     In one exemplary embodiment, the Low Power Mode may be implemented to save power for VPU  20 . The Low Power Mode may be entered, for example, anytime the VPU  20  does not receive back telemetry from the Retinal stimulation system. Upon entry to the Low Power Mode, the VPU  20  turns off power to the Retinal stimulation system. After that, and periodically, the VPU  20  turns power back on to the Retinal stimulation system for an amount of time just long enough for the presence of the Retinal stimulation system to be recognized via its back telemetry. If the Retinal stimulation system is not immediately recognized, the controller again shuts off power to the Retinal stimulation system. In this way, the controller ‘polls’ for the passive Retinal stimulation system and a significant reduction in power used is seen when the Retinal stimulation system is too far away from its controller device.  FIG. 10 b    depicts an exemplary block diagram  900  of the steps taken when the VPU  20  does not receive back telemetry from the Retinal stimulation system. If the VPU  20  receives back telemetry from the Retinal stimulation system (output “YES” of step  901 ), the Retinal stimulation system may be provided with power and data (step  906 ). If the VPU  20  does not receive back telemetry from the Retinal stimulation system (output “NO” of step  901 ), the power to the Retinal stimulation system may be turned off. After some amount of time, power to the Retinal stimulation system may be turned on again for enough time to determine if the Retinal stimulation system is again transmitting back telemetry (step  903 ). If the Retinal stimulation system is again transmitting back telemetry (step  904 ), the Retinal stimulation system is provided with power and data (step  906 ). If the Retinal stimulation system is not transmitting back telemetry (step  904 ), the power to the Retinal stimulation system may again be turned off for a predetermined amount of time (step  905 ) and the process may be repeated until the Retinal stimulation system is again transmitting back telemetry. 
     In another exemplary embodiment, the Low Power Mode may be entered whenever the subject is not wearing the Glasses  5 . In one example, the Glasses  5  may contain a capacitive touch sensor (not shown) to provide the VPU  20  digital information regarding whether or not the Glasses  5  are being worn by the subject. In this example, the Low Power Mode may be entered whenever the capacitive touch sensor detects that the subject is not wearing the Glasses  5 . That is, if the subject removes the Glasses  5 , the VPU  20  will shut off power to the external coil  17 . As soon as the Glasses  5  are put back on, the VPU  20  will resume powering the external coil  17 .  FIG. 10 c    depicts an exemplary block diagram  910  of the steps taken when the capacitive touch sensor detects that the subject is not wearing the Glasses  5 . If the subject is wearing Glasses  5  (step  911 ), the Retinal stimulation system is provided with power and data (step  913 ). If the subject is not wearing Glasses  5  (step  911 ), the power to the Retinal stimulation system is turned off (step  912 ) and the process is repeated until the subject is wearing Glasses  5 . 
     One exemplary embodiment of the VPU  20  is shown in  FIG. 11 . The VPU  20  may comprise: a Power Supply, a Distribution and Monitoring Circuit (PSDM)  1005 , a Reset Circuit  1010 , a System Main Clock (SMC) source (not shown), a Video Preprocessor Clock (VPC) source (not shown), a Digital Signal Processor (DSP)  1020 , Video Preprocessor Data Interface  1025 , a Video Preprocessor  1075 , an I 2 C Protocol Controller  1030 , a Complex Programmable Logic device (CPLD) (not shown), a Forward Telemetry Controller (FTC)  1035 , a Back Telemetry Controller (BTC)  1040 , Input/Output Ports  1045 , Memory Devices like a Parallel Flash Memory (PFM)  1050  and a Serial Flash Memory (SFM)  1055 , a Real Time Clock  1060 , an RF Voltage and Current Monitoring Circuit (VIMC) (not shown), a speaker and/or a buzzer, an RF receiver  1065 , and an RF transmitter  1070 . 
     The Power Supply, Distribution and Monitoring Circuit (PSDM)  1005  may regulate a variable battery voltage to several stable voltages that apply to components of the VPU  20 . The Power Supply, Distribution and Monitoring Circuit (PSDM)  1005  may also provide low battery monitoring and depleted battery system cutoff. The Reset Circuit  1010  may have reset inputs  1011  that are able to invoke system level rest. For example, the reset inputs  1011  may be from a manual push-button reset, a watchdog timer expiration, and/or firmware based shutdown. The System Main Clock (SMC) source is a clock source for DSP  1020  and CPLD. The Video Preprocessor Clock (VPC) source is a clock source for the Video Processor. The DSP  1020  may act as the central processing unit of the VPU  20 . The DSP  1020  may communicate with the rest of the components of the VPU  20  through parallel and serial interfaces. The Video Processor  1075  may convert the NTSC signal from the camera  13  into a down-scaled resolution digital image format. The Video Processor  1075  may comprise a video decoder (not shown) for converting the NTSC signal into high-resolution digitized image and a video scaler (not shown) for scaling down the high-resolution digitized image from the video decoder to an intermediate digitized image resolution. The video decoder may be composed of an Analog Input Processing, Chrominance and Luminance Processing and Brightness Contrast and Saturation (BSC) Control circuits. The video scaler may be composed of Acquisition control, Pre-scaler, BSC-control, Line Buffer and Output Interface. The I 2 C Protocol Controller  1030  may serve as a link between the DSP  1020  and the I 2 C bus. The I 2 C Protocol Controller  1030  may be able to convert the parallel bus interface of the DSP  1020  to the I 2 C protocol bus or vice versa. The I 2 C Protocol Controller  1030  may also be connected to the Video Processor  1075  and the Real Time Clock  1060 . The VPDI  1025  may contain a tri-state machine to shift video data from Video Preprocessor  1075  to the DSP  1020 . The Forward Telemetry Controller (FTC)  1035  packs  1024  bits of forward telemetry data into a forward telemetry frame. The FTC  1035  retrieves the forward telemetry data from the DSP  1020  and converts the data from logic level to biphase marked data. The Back Telemetry Controller (BTC)  1040  retrieves the biphase marked data from the RF receiver  1065 , decodes it, and generates the BFSR, BCLKR and BDR for the DSP  1020 . The Input/Output Ports  1045  provide expanded IO functions to access the CPLD on-chip and off-chip devices. The Parallel Flash Memory (PFM)  1050  may be used to store executable code and the Serial Flash Memory (SFM)  1055  may provide Serial Port Interface (SPI) for data storage. The VIMC may be used to sample and monitor RF transmitter  1070  current and voltage in order to monitor the integrity status of the retinal stimulation system. 
     Accordingly, what has been shown is an improved visual prosthesis. 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.