Method and apparatus for fitting a visual prosthesis using electrically evoked electroretinograms

Patent metadata

Field	Value
Publication number	US-10292579-B2
Application number	US-201113311264-A
Country	US
Kind code	B2
Filing date	Dec 5, 2011
Priority date	Dec 3, 2010
Publication date	May 21, 2019
Grant date	May 21, 2019

Abstract

The invention is a method of automatically adjusting a retinal electrode array to the neural characteristics of an individual patient. By recording electrically evoked electroretinograms (eERG) to a predetermined input stimulus, one can alter that input stimulus to the needs of an individual patient. A minimum input stimulus is applied to a patient, followed by recording the eERG response to the input stimulus. By gradually increasing stimulus levels, one can determine the minimum input that creates a neural response, thereby identifying the threshold stimulation level. One can further determine a maximum level by increasing stimulus until a predetermined maximum neural response is obtained. However, eERG signals include a significant amount of noise. Applicants have developed novel techniques for artifact reduction and noise filtering to provide an accurate measure of neural activity.

First claim

What is claimed is:

1. A method of fitting an implantable neural stimulator comprising:
a. providing an implantable neural stimulator including electrical components and an array of electrodes suitable to stimulate visual neurons within an eye and suitable to be implanted in the eye;
b. providing a computer, the computer completing steps c through m under automatic control of the computer;
c. stimulating the visual neurons with a series of electrical stimulation signals through a selected subset of the array of electrodes to the eye;
d. using an electroretinogram to record levels of measured neural activity induced by the step of stimulating the visual neurons to produce electroretinogram signals of the measured neural activity;
e. filtering the electroretinogram signals to remove signals from eye movement or pupil responses;
f. applying a wavelet transform to the electroretinogram signals to filter out any electroretinogram artifacts caused by the electrical components in the implantable neural stimulator;
g. discarding the electroretinogram signals with large artifacts;
h. averaging epochs in the electroretinogram signals;
i. comparing each level of the neural activity measured by the electroretinogram to the stimulation signals;
j. determining a relationship between the stimulation signals and each level of the neural activity measured by the electroretinogram;
k. repeating steps c-j for different selected subsets of the array of electrodes;
l. determining and storing desired levels of stimulation based upon the comparison of the level of the neural activity measured by the electroretinogram and a stimulation level of the stimulation signals; and
m. stimulating the visual neurons in the eye with the implantable neural stimulator to induce the perception of vision based on the desired levels of stimulation.

2. The method according to claim 1 , further comprising detecting neural activity in a fellow eye using the electroretinogram and subtracting the neural activity measured by the electroretinogram in the fellow eye from the neural activity measured by the electroretinogram in the eye, wherein the fellow eye does not have the implantable neural stimulator.

3. The method according to claim 1 , wherein the step of stimulating the visual neurons includes increasing the electrical charge of the electrical stimulation signals until the neural activity, measured by the electroretinogram, is detected.

4. The method according to claim 1 , wherein said step of stimulating the visual neurons includes decreasing the electrical stimulation signals when a predetermined level of the neural activity, measured by the electroretinogram, is reached.

5. The method according to claim 1 , further comprising analysis of the delay period between the step of stimulating the visual neurons and the measuring of the neural activity by the electroretinogram, wherein the delay period varies according to a level of input stimulus, and this variation is used in the fitting process.

6. The method according to claim 1 , wherein storing a level of stimulation includes storing a threshold for each electrode in the array of electrodes.

7. The method according to claim 1 , further comprising averaging multiple epochs of the neural activity measured by the electroretinogram.

8. The method according to claim 1 , further comprising ignoring the neural activity measured by the electroretinogram greater than a predetermined voltage.

9. The method according to claim 8 , wherein the predetermined voltage is between 40 μV and 60 μV.

10. A system for fitting a visual prosthesis comprising:
a visual prosthesis suitable to stimulate visual neurons within an eye including electrical components and an array of electrodes to output stimulation signals;
an electroretinogram including a corneal electrode suitable to fit the eye and configured to record neural signal levels induced by stimulation of the visual neurons by the stimulation signals to produce electroretinogram signals of measured neural activity;
a computer and a filter configured to:
filter the electroretinogram signals to remove signals from eye movement or pupil responses,
apply a wavelet transform to the electroretinogram signals to filter out any electroretinogram artifacts caused by the electrical components in the visual prosthesis,
discard the electroretinogram signals with large artifacts,
average epochs in the electroretinogram signals,
compare each level of the neural activity measured by the electroretinogram to the stimulation signals,
determine a relationship between the stimulation signals and each level of the neural activity measured by the electroretinogram, and
determine and store desired levels of stimulation based upon the comparison of the level of the neural activity measured by the electroretinogram and a stimulation level of the stimulation signals
stimulate the visual neurons in the eye with the visual prosthesis to induce the perception of vision based on the desired levels of stimulation;
and

a non-transitory memory in the computer for storing the desired stimulation levels individually for multiple subsets of the array of electrodes as identified by the visual prosthesis and the electroretinogram.

11. The system for fitting a visual prosthesis according to claim 10 , wherein the electroretinogram is configured to record with a second corneal electrode and suitable to obtain simultaneous and equivalent recordings from the fellow eye and the implanted eye, wherein the fellow eye does not have the visual prosthesis.

12. The system for fitting a visual prosthesis according to claim 10 , wherein the memory is configured to store threshold stimulation levels for each electrode within the array of electrodes.

13. The system for fitting a visual prosthesis according to claim 11 , wherein the computer is configured to subtract electroretinogram signals of the second corneal electrode from the electroretinogram signals of the corneal electrode.

14. The system for fitting a visual prosthesis according to claim 10 , wherein the computer is configured for discarding the electroretinogram signals from the electroretinogram indicating a signal greater than a predetermined level.

15. The system for fitting a visual prosthesis according to claim 14 , wherein the predetermined level is between 40 μV and 60 μV.

16. The system for fitting a visual prosthesis according to claim 10 , wherein the memory is configured to store stimulation thresholds and stimulation maxima for each electrode in the array of electrodes.

17. The system for fitting a visual prosthesis according to claim 10 , the computer of the visual prosthesis is configured to alter stimulation levels in the visual prosthesis according to the desired stimulation levels stored in the non-transitory memory based on the electroretinogram.

18. The method according to claim 1 , further comprising tracking eye movement to determine a signal caused by eye movement and subtracting the signal caused by eye movement from the electroretinogram signal.

Assignees

• Greenberg Robert J
• Dagnelie Gislin
• Stronks Hendrik Christiaan
• Second Sight Medical Products Inc

Inventors

• Greenberg Robert J
• Dagnelie Gislin
• Stronks Hendrik Christiaan

Classifications

• A61B3/0025 Primary

  characterised by electronic signal processing, e.g. eye models · CPC title

• A61N1/36046

  of the eye · CPC title

• A61B5/0496

  Human Necessities · mapped topic

• A61B5/398

  Electrooculography [EOG], e.g. detecting nystagmus; Electroretinography [ERG] · CPC title