Abstract
Purpose: :
To ascertain the ability of subjects to use the Argus II retinal prosthesis to visually guide fine hand motion.
Methods: :
Subjects used a touch screen monitor displaying a white path on a black background, and traced along the path, with the software recording contact and timing. Subjects were trained by receiving auditory feedback whenever tracing outside the path. The testing mode provides no feedback other than to indicate the start and end points of the trace, or warn the subject if screen contact is lost. All start and end points were near screen corners, allowing subjects to start and end the task without vision. Ten subjects trained and tested with a set of paths with single right angles, and then trained and tested with a set of paths with single acute, right, or obtuse angles, deemed to be less predictable.
Results: :
Across all trials, error in tracing the paths decreases by 58% when using the Argus II retinal prosthesis, compared to performance without using the prosthesis (p < .001, 2-tailed unpaired t-test). Time to finish tracing a path increases by 207% when subjects use the prosthesis, compared to using natural vision (p < .001, 2-tailed t-test). Analyzing the two test sets separately, the right angle test has only two possible paths connecting the start and end points, while the mixed angles test has many possible paths. Of trials in which subjects with no light perception used the prosthesis for the first test, 91% have the subject choosing the correct direction of the path (p < .001, 1-tailed binomial test). In contrast, and as expected, these subjects chose the correct direction in 51% of trials without the prosthesis. Subjects with light perception were also less likely to choose the incorrect direction with prosthesis active, but not significantly. Similar differences as seen across all trials are observed in error area and time measurements while using the prosthesis for the less predictable second test; error areas with obtuse-angle paths, however, are consistently increased above the other path designs - by 90% (p < 0.01, 2-tailed t-test) using the implant and by 70% (p < 0.01, 2-tailed t-test) not using the implant.
Conclusions: :
Use of the ArgusTM II retinal prosthesis improves subjects’ abilities to visually guide fine hand motion. Prosthesis use also seems to promote more meticulous tracing, reflected by the 3-fold increase in tracing time. Further, the benefit of the prosthesis over natural vision seems to appear most clearly when tracing less predictable paths, particularly the obtuse paths used in the second test. Additional data from similar experiments utilizing this aspect are being collected.
Clinical Trial: :
www.clinicaltrials.gov NCT00407602
Keywords: clinical (human) or epidemiologic studies: treatment/prevention assessment/controlled clinical trials • retinal degenerations: hereditary • low vision