System and method for selective retinal stimulation

1. A method for electrically stimulating a retina of an eye to induce visual perception, said method comprising the steps of:

placing an electrode within the eye in proximity to a retinal ganglion cell (RGC) layer; and

applying a biphasic, asymmetrical, charge-balanced waveform to at least a portion of the RGC layer,

said biphasic, asymmetrical, charge-balanced waveform comprising:

a pre-pulse phase having a first polarity, a sub-threshold first amplitude, and a first duration to change the excitability of at least one cell related to the at least the portion of the RGC layer; and

a stimulation-pulse phase following the pre-pulse phase having a second polarity opposite the first polarity, a supra-threshold second amplitude, and a second duration less than the first duration to induce visual perception.

2. The method of claim 1 , wherein said stimulation-pulse phase follows said pre-pulse phase.

3. The method of claim 1 , wherein the first polarity is a cathodic polarity and the second polarity is an anodic polarity to induce visual perception of a circular shape.

4. The method of claim 3 , wherein the first duration is of a duration sufficient to increase excitability of a passing region of an axon in a nerve fiber layer adjacent to the portion of the RGC layer.

5. The method of claim 1 , wherein the first polarity is an anodic polarity and the second polarity is a cathodic polarity to induce perception of an elongated shape.

6. The method of claim 5 , wherein the first duration is sufficient to increase excitability of an approximately 90° bending region of the at least one cell.

7. The method of claim 1 , wherein said step of placing an electrode within the eye adjacent a RGC layer further includes placing said electrode within the eye adjacent an approximately 90° bending region of the RGC layer.

8. The method of claim 1 , wherein a charge delivered by said stimulation-pulse phase balances a charge delivered by said pre-pulse phase.

9. The method of claim 1 , wherein said first duration of said pre-pulse phase is approximately ten times longer than said second duration of said stimulation-pulse phase.

10. The method of claim 1 , wherein said biphasic, asymmetrical, charge-balanced waveform further comprises an interphase delay between said pre-pulse phase and said stimulation-pulse phase.

11. A method for electrically stimulating a retina of an eye to induce visual perception, said method comprising the steps of:

placing an electrode within the eye in proximity to a retinal ganglion cell (RGC) layer; and

selecting a first polarity and a second polarity of a biphasic, asymmetrical, charge balanced waveform, wherein the second polarity is opposite to the first polarity, wherein the first polarity and the second polarity are selected to induce a visual perception;

applying the biphasic, asymmetrical, charge balanced waveform to at least a portion of the RGC layer,

said biphasic, asymmetrical, charge-balanced waveform comprising:

a pre-pulse phase comprising the first polarity, a sub-threshold first amplitude, and a first duration to change the excitability of at least one cell related to the at least the portion of the RGC layer; and

a stimulation-pulse phase comprising the second polarity, a supra-threshold second amplitude, and a second duration less than the first duration to induce the visual perception.

12. The method of claim 11 , wherein the first polarity is cathodic, the second polarity is anodic, and the visual perception comprises the perception of a circular shape; or

wherein the first polarity is anodic, the second polarity is cathodic, and the visual perception comprises the perception of an elongated shape.

13. A method for electrically stimulating a retina of an eye to induce visual perception, said method comprising the steps of:

placing an electrode within the eye in proximity to a retinal ganglion cell (RGC) layer; and

selecting parameters to balance the charge of a biphasic, asymmetrical waveform, wherein the parameters include:

first parameters of a pre-pulse phase comprising a first polarity, a sub-threshold first amplitude, and a first duration, and

second parameters of a stimulation-pulse phase comprising a second polarity opposite to the first polarity, a supra-threshold second amplitude, and a second duration at least ten times shorter than the first duration;

applying the biphasic, asymmetrical waveform with the charge balanced according to the selected parameters to at least a portion of the RGC layer,

said biphasic, asymmetrical waveform comprising:

the pre-pulse phase comprising the first polarity, the sub-threshold first amplitude, and the first duration to change the excitability of at least one cell related to the at least the portion of the RGC layer; and

the stimulation-pulse phase comprising the second polarity, the supra-threshold second amplitude, and the second duration to induce the visual perception;

wherein the first polarity is cathodic, the second polarity is anodic, and the visual perception induced is of a circular shape; or

wherein the first polarity is anodic, the second polarity is cathodic, and the visual perception induced is of an elongated shape.