Use of the Argus II retinal prosthesis to improve visual guidance of fine hand movements

Abstract

Purpose: We studied the capabilities of the Argus II retinal prosthesis for guiding fine hand movement, and demonstrated and quantified guidance improvement when using the device over when not using the device for progressively less predictable trajectories.

Methods: A total of 21 patients with retinitis pigmentosa (RP), remaining vision no more than bare light perception, and an implanted Argus II epiretinal prostheses used a touchscreen to trace white paths on black backgrounds. Sets of paths were divided into three categories: right-angle/single-turn, mixed-angle/single-turn, and mixed-angle/two-turn. Subjects trained on paths by using prosthetic vision and auditory feedback, and then were tested without auditory feedback, with and without prosthetic vision. Custom software recorded position and timing information for any contact that subjects made with the screen. The area between the correct path and the trace, and the elapsed time to trace a path were used to evaluate subject performance.

Results: For right-angle/single-turn sets, average tracing error was reduced by 63% and tracing time increased by 156% when using the prosthesis, relative to residual vision. With mixed-angle/single-turn sets, error was reduced by 53% and time to complete tracing increased by 184%. Prosthesis use decreased error by 38% and increased tracing time by 252% for paths that incorporated two turns.

Conclusions: Use of an epiretinal visual prosthesis can allow RP patients with no more than bare light perception to guide fine hand movement visually. Further, prosthetic input tends to make subjects slower when performing tracing tasks, presumably reflecting greater effort. (ClinicalTrials.gov number, NCT01123928.)

Trial registration: ClinicalTrials.gov NCT00407602 NCT01123928 NCT00407602.

Conflict of interest statement

Disclosure: M.P. Barry, Second Sight Medical Products (F); G. Dagnelie, Second Sight Medical Products (F)

Figures

Figure 1.

The above frames show screens that were presented to the subjects in chronologic order for each trial. The first green screen appeared before any trial began. Upon touching the screen, the start point of the path would appear (center panel). Upon touching the start point, the rest of the path appeared for the subject to trace.

Figure 2.

This image is an example of a right-angle path.

Figure 3.

The above images are examples of path classes introduced for the mixed, single-angle tests. Each path here starts in the upper left corner. Each class is defined by the position of the turn relative to the start point and the general angle of the turn. Different members of a class are generated by horizontally, vertically, and diagonally flipping configurations.

Figure 4.

The above images are examples of two-turn paths.

Figure 5.

The above graph displays error scores for right-angle paths. Points represent error scores for individual trials, chronologically ordered across all non–light-perceiving subjects. The predictable nature of the paths created an approximate two-alternative forced-choice test. Subjects typically traced conforming to a right angle path, and most of the variability arose from whether they chose the correct orientation of the path. Closed symbols: system-on trials. Open symbols: system-off trials. Percent correct (<65 pixels error) given system-on: 95% (P < 0.001, binomial test).

Figure 6.

Left graph: normalized error scores from the mixed, single-angle tests. Right graph: normalized time to trace paths in the mixed, single-angle tests. Error areas and times were divided by path lengths (in pixels) to obtain the normalized scores shown here. Points indicate average performance for each subject. Error bars denote SEM. Diagonal lines represent the identity line. In general, system-on status reduced error and increased trace time.

Figure 7.

Average performance for each subject, system-on, for the mixed-angle paths. Error areas and times were divided by path lengths (in pixels) to normalize scores, and transformed using the square root operation. Error bars denote SEM. Subject performance with the prosthesis, in both speed and accuracy, was highly varied.

Figure 8.

Left graph: error scores from the two-turn tests. Right graph: the time to trace paths in two-turn tests. Error areas and times were divided by path lengths (in pixels) to normalize scores. Points indicate average performance for each subject. Error bars denote SEM. Diagonal lines represent the identity line. Prosthesis use reduced error and increased time to trace paths.