System and method for selective retinal stimulation

Abstract

A method for selective electrical stimulation of a retina for application in a visual neuralprosthesis. The method includes application of an asymmetrical, charge-balance biphasic waveform to increase the receptivity of selected cells to a subsequent stimulus, and then electrically stimulating to those selected cells to induce either a punctuate phosphene (perceived spot of light in the visual field) or a streak phosphene (streak of light in the visual field). A waveform having a sub-threshold anodic pulse followed by a supra-threshold cathodic pulse induces the punctuate phosphene, and a sub-threshold cathodic pulse followed by a supra-threshold anodic pulse induces the streak phosphene.

1 . A method for electrically stimulating a retina of an eye to induce visual perception, comprising the following steps: 
 placing an electrode adjacent a retinal ganglion cell layer;    effecting a change in the excitability of cells in the ganglion cell layer by selectively applying a biphasic asymmetrical waveform having a relatively long duration and relatively low amplitude pre-pulse phase of a first polarity; and    inducing visual perception by selectively applying a biphasic asymmetrical waveform having a relatively short duration and relatively high amplitude stimulation pulse phase of a second polarity opposite the first polarity following the pre-pulse phase;    wherein a cathodic pre-pulse phase and an anodic stimulation phase induce the perception of a circular shape, and an anodic pre-pulse phase and a cathodic stimulation phase induce the perception of an elongate shape.    
   
   
       2 . A method as set forth in  claim 1 , wherein the effecting and inducing steps are accomplished by applying an asymmetrical charged-balanced biphasic waveform.  
   
   
       3 . A method as set forth in  claim 1 , wherein the effecting step includes applying the anodic pre-pulse phase at a magnitude that is below a threshold value at which ganglion nerve cells are triggered and for a duration that is sufficient to increase the excitability of the bending region of an axon.  
   
   
       4 . A method as set forth in  claim 1 , wherein the effecting step includes applying the cathodic pre-pulse phase at a magnitude that is sub-threshold and for a duration sufficient to increase the excitability of the passing region of an axon.  
   
   
       5 . A method as set forth in  claim 1 , wherein the inducing step includes applying the stimulation pulse phase at a supra-threshold magnitude that balances the charge injected by the pre-pulse phase.  
   
   
       6 . A method as set forth in  claim 1 , wherein the effecting step includes applying a pre-pulse phase for no more than about half a millisecond.  
   
   
       7 . A method as set forth in  claim 1 , wherein the duration of the stimulation pulse phase to the duration of the pre-pulse phase is approximately 10:1.  
   
   
       8 . A method comprising the steps of 
 placing an electrode adjacent a retinal ganglion cell layer;    effecting a change in the excitability of cells in the ganglion cell layer by selectively applying a biphasic asymmetrical waveform that has a pre-pulse phase having a first polarity, a first amplitude and a first duration, the first amplitude and first duration together defining a pre-pulse charge having a first magnitude and the first polarity; and a stimulation-pulse phase following the pre-pulse phase, the stimulation-pulse phase having a second polarity opposite the first polarity, a second amplitude and second duration less than the first duration, the second amplitude and second duration together defining a stimulation charge having the second polarity and a second magnitude that equals the first magnitude.    
   
   
       9 . A visual neuroprosthesis for electrically stimulating a retina of an eye to induce visual perception, comprising an electrode positionable near a ganglion cell layer of the retina of an eye; and a waveform generator capable of generating a waveform for selectively stimulating either bending axons to induce the perception of a circular image or passing axons to induce the perception of an elongated image.