Method and apparatus for visual neural stimulation

Abstract

Existing epiretinal implants for the blind are designed to electrically stimulate large groups of surviving retinal neurons using a small number of electrodes with diameters of several hundred μm. To increase the spatial resolution of artificial sight, electrodes much smaller than those currently in use are desirable. In this study we stimulated and recorded ganglion cells in isolated pieces of rat, guinea pig, and monkey retina. We utilized micro-fabricated hexagonal arrays of 61 platinum disk electrodes with diameters between 6 and 25 μm, spaced 60 μm apart. Charge-balanced current pulses evoked one or two spikes at latencies as short as 0.2 ms, and typically only one or a few recorded ganglion cells were stimulated. Application of several synaptic blockers did not abolish the evoked responses, implying direct activation of ganglion cells. Threshold charge densities were typically below 0.1 mC/cm2 for a pulse duration of 100 μs, corresponding to charge thresholds of less than 100 pC. Stimulation remained effective after several hours and at high frequencies. To demonstrate that closely spaced electrodes can elicit independent ganglion cell responses, we utilized the multi-electrode array to stimulate several nearby ganglion cells simultaneously. From these data we conclude that electrical stimulation of mammalian retina with small-diameter electrode arrays is achievable and can provide high temporal and spatial precision at low charge densities. We review previous epiretinal stimulation studies and discuss our results in the context of 32 other publications, comparing threshold parameters and safety limits.

1 . An electrode array for stimulating visual neurons comprising: 
 A non-conductive body;    A plurality of conductive electrodes wherein said electrode are less than 20 μm in size and less than 60 μm apart; and    means for supporting said body in close proximity to visual neurons.    
   
   
       2 . The electrode array according to  claim 1 , wherein said electrodes are arranged hexagonally.  
   
   
       3 . The electrode array according to  claim 1 , wherein said non-conductive body is a fluoro-polymer  
   
   
       4 . The electrode array according to  claim 1 , wherein said electrodes are arranged in a pattern longer in one dimension than the other dimension; and 
 Wherein said one dimension corresponds to horizontal in a visual scene.    
   
   
       5 . A flexible circuit electrode array adapted for neural stimulation comprising: 
 A polymer base layer;    Metal traces deposited on said polymer base layer, including electrodes suitable to stimulate neural tissue; and    A polymer top layer deposited on said polymer base layer and said metal traces;    Wherein said polymer top layer defines openings smaller than said electrodes to overlap said electrodes.    
   
   
       6 . A flexible circuit electrode array adapted for neural stimulation comprising: 
 A polymer base layer;    Metal traces deposited on said polymer base layer, including electrodes suitable to stimulate neural tissue; and    A polymer top layer deposited on said polymer base layer and said metal traces;    wherein said electrodes are less than 20. μm in size and less than 60 μm apart    
   
   
       7 . The flexible circuit electrode array according to  claim 6 , wherein said polymer base layer, said metal traces and said polymer top layer are curved to approximately the curvature of an eye.  
   
   
       8 . The flexible circuit electrode array according to  claim 6 , further comprising at least one bumper bonded to a peripheral edge of said flexible circuit electrode array.  
   
   
       9 . The flexible circuit electrode array according to  claim 6 , further comprising a narrowed portion in a flexible circuit cable portion of said flexible circuit electrode array.  
   
   
       10 . The flexible circuit electrode array according to  claim 6 , further comprising a stress relief membrane suitable for attachment of said flexible circuit electrode array, wherein said stress relief membrane is a more compliant material than said polymer base layer.  
   
   
       11 . The flexible circuit electrode array according to  claim 9 , wherein said narrowed portion is suitable to pierce a sclera.  
   
   
       12 . The flexible circuit electrode array according to  claim 11 , wherein said narrowed portion is a diagonal fold in a flexible circuit cable portion of said flexible circuit electrode array.  
   
   
       13 . The flexible circuit electrode array according to  claim 12 , where said diagonal fold is across a dogleg in said flexible circuit electrode array.  
   
   
       14 . The flexible circuit electrode array according to  claim 13 , further comprising bond pads coupled to said metal traces on an end of said flexible circuit electrode array opposite to said electrodes and openings in said polymer top layer for said electrodes and said bond pads.  
   
   
       15 . The flexible circuit electrode array according to  claim 8 , where said bumper is a continuous skirt covering at least of portion of said flexible circuit electrode array.  
   
   
       16 . The flexible circuit electrode array according to  claim 8 , where said bumper is a continuous skirt covering at least of portion of a cable portion of said flexible circuit electrode array.  
   
   
       17 . The flexible circuit electrode array according to  claim 16 , further comprising a sleeve at least partially covering a flexible circuit cable portion of said flexible circuit electrode array.  
   
   
       18 . The flexible circuit electrode array according to  claim 17 , wherein said sleeve and said bumper are a continuous body.  
   
   
       19 . The flexible circuit electrode array according to  claim 6 , wherein said polymer base layer, said metal traces and said polymer top layer for a continuous electrode array and flexible circuit cable where said flexible circuit cable forms a partial loop to resist transmission of forces through said flexible circuit cable.  
   
   
       20 . The flexible circuit electrode array according to  claim 6 , wherein said electrodes are arranged in a hexagonal pattern.