Eye movement control in Argus II retinal prosthesis users improves performance in a shape localization task

Abstract

Purpose : The Argus II retinal prosthesis is an approved treatment to restore sight and has been implanted in more than 200 blind patients worldwide. In contrast to scanning with the eyes by sighted individuals, scanning the scene with the Argus II is done by camera – i.e., head – movements. Here, we tested if a scanning mode based on patient’s eye movements will increase visual stability.

Methods : Eye positions were measured in real time using a head-mounted eye tracker. The eye positions were used to shift the region of interest (ROI) that is sent to the implant within the wide field-of-view (FOV) of the head-mounted scene camera. Subjects were able to use combined eye-head scanning: Shifting the scene camera by moving the head and shifting the ROI within the camera FOV by moving the eye. Four Argus II implantees, three males and one female, participated in the study. A white target appeared on a touch-screen monitor and the patients were instructed to report the location of the target by touching the monitor. We compared the spread of the responses between the combined eye-head and the head-only scanning. The mean error can be corrected, by image shifting, but the spread around the mean, i.e. standard deviation, is an indication of the precision across trials. The F-test was used to compare the standard deviation along the horizontal and vertical axes between the scanning modes. As we have tests along two dimensions for each patient, based on the Bonferroni correction the critical p-value was set to 0.025

Results : Spreads of one patient’s responses relative to the target position with eye-head and head-only scanning is shown in the attached figures. The standard deviations of the responses for each scanning mode along the horizontal and vertical axes are given in the attached table. The F-test shows that for all patients there is a narrower spread in one axis using combined eye-head scanning.

Conclusions : Integrating an eye tracker into the Argus II to shift the region-of-interest based on eye position for eye-head scanning is feasible and improves pointing precision.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

 

Reported percept location relative to the target location in each trial. Left panel: head-only scanning. Right panel: eye-head scanning.

 

Spread of patients’ responses as quantified by standard deviations for the two scanning conditions. Cases that are larger than the critical F-value of 1.89 are marked with (*).