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A. K. Ahuja, J. D. Dorn, A. Caspi, E. Filley, G. Dagnelie, R. J. Greenberg, M. J. McMahon; The Argus II Retinal Prosthesis Enables Blind Subjects to Identify the Direction of Motion. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4590.
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The feasibility of the Argus II chronic epi-retinal implant to partially restore vision to subjects blinded by photoreceptor degeneration is currently under investigation in several clinical centers worldwide. The purpose of this work was to test whether the Argus II retinal prosthesis system improved the ability of blind subjects to determine the direction of an object moving in the visual field.
Subjects implanted with an Argus II retinal prosthesis viewed the center of a 19" touchscreen monitor placed 12" in front of their eyes. After an audio prompt, a white line of fixed width swept across the black monitor screen at a randomly chosen angle (0-360°). Subjects were instructed not to scan and to maintain fixation on the center of the screen during the stimulus presentation. After the line moved across the entire screen, the subjects drew the direction of motion they perceived on the touchscreen. The speed of the motion was fixed throughout the experiment, but varied across subjects (the best speed for each subject was selected from three options: 1s, 2s, or 8s to cross the screen). An experiment consisted of 80 trials with automated verbal feedback. The experiment was repeated with the system on and off for each subject.
The error (difference between the direction of the moving line and the direction drawn by the subject) was calculated for each trial. Seven subjects had significantly different error distributions (Kolmogorov-Smirnov test, p<0.05) and gave more correct responses (within 15° of the stimulus angle) with the system on than with the system off. Four subjects did not have significantly different error distributions with the system on vs. off.
The Argus II retinal prosthesis improved the ability of blind subjects to identify the direction of a moving object, a task that requires spatio-temporal information from multiple stimulating electrodes. This is consistent with results from the Argus I clinical trial demonstrating the ability to use spatial information from multiple electrodes (McMahon et al., 2007).
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