Blind subjects implanted with the Argus II retinal prosthesis are able to improve performance in a spatial-motor task

Abstract

Background/aims: To determine to what extent subjects implanted with the Argus II retinal prosthesis can improve performance compared with residual native vision in a spatial-motor task.

Methods: High-contrast square stimuli (5.85 cm sides) were displayed in random locations on a 19″ (48.3 cm) touch screen monitor located 12″ (30.5 cm) in front of the subject. Subjects were instructed to locate and touch the square centre with the system on and then off (40 trials each). The coordinates of the square centre and location touched were recorded.

Results: Ninety-six percent (26/27) of subjects showed a significant improvement in accuracy and 93% (25/27) show a significant improvement in repeatability with the system on compared with off (p<0.05, Student t test). A group of five subjects that had both accuracy and repeatability values <250 pixels (7.4 cm) with the system off (ie, using only their residual vision) was significantly more accurate and repeatable than the remainder of the cohort (p<0.01). Of this group, four subjects showed a significant improvement in both accuracy and repeatability with the system on.

Conclusion: In a study on the largest cohort of visual prosthesis recipients to date, we found that artificial vision augments information from existing vision in a spatial-motor task. Clinical trials registry no NCT00407602.

Figure 1

A schematic illustration showing the surgically implanted stimulating microelectrode array, and inductive coil telemetry link of the Argus II system (left). The external portions of the system consist of a video processing unit (VPU) (middle) and a miniature camera mounted on a pair of glasses (right).

Figure 2

Results from square localisation experiments of nine representative subjects with the system off and on. Plots are normalised to square centre; responses (white circles) are plotted relative to target square location (axes units are in pixels). Standard deviations of the mean of all responses in an experiment are indicated (dotted line). The subjects are plotted from smallest (top left) to largest (bottom right) factor of improvement in accuracy (system on vs off).

Figure 3

Mean distance from target square centre (pixels) for each subject with system on (black square) and off (white circles). Range of standard error of mean is shown by vertical bars. Subjects are plotted in order of increasing factor of improvement in accuracy (system on vs off).

Figure 4

Repeatability (pixels) versus accuracy (pixels) for all subjects with system on (top) and system off (bottom). Linear regression (dashed line) for system off (y=1.00x–22.9; R²=0.90) and system on (y=0.82x+ 7.9; R²=0.88) shows a good correlation between subject’s ability mean response distance from target and the clustering of their responses. The five subjects (JHU-003, LON-001, JHU-005, MAN-001 and PENN-001) that had success with the task with their native vision are clearly separated from the rest of the cohort in the system off plot.

Figure 5

Results from square localisation experiments with the system off (top) and on (bottom) for JHU-001, MAN-001 and PENN-001. Plots are normalised to square centre; responses (empty circles) are plotted relative to target square location (axes units are in pixels). Standard deviations of the mean of all responses in an experiment are indicated (dotted line). Although all subjects could perform the task with their native vision, years of visual deprivation effect of spatial-motor feedback. Two of three (MAN-001 and PENN-001) of these subjects’ accuracy and repeatability improved with the system on.