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M. J. McMahon, J. D. Dorn, A. K. Ahuja, A. Caspi, E. Filley, G. Dagnelie, R. J. Greenberg; The Argus II Retinal Prosthesis Enables Blind Subjects to Localize Objects. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4589.
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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 system improves the ability of blind subjects to localize objects in laboratory tests (visual stimuli presented on a monitor) and in real world tasks (walking in a controlled environment).
In the first experiment, white square stimuli were displayed in random locations on a 19" touchscreen monitor located 12" in front of the subject. After the onset of the square and an auditory prompt, the subject was instructed to locate the square and touch the monitor in the center of its perceived location. Performance was quantified in two ways: accuracy (the average distance between each response and the center of the target square) and clustering (the average distance between each response and the mean of all responses). In the second experiment, the subject attempted to walk to a 3'x7' "door" (black felt on a light-colored wall) 20' from their starting location. The distance between the location the subject touched on the wall and the edge of the "door" was measured for each trial (a touch on any part of the door was recorded as 0"). For both tasks, performance was compared with the system on and off.
In the square localization experiment, eight subjects' responses were significantly more accurate and more clustered with the system on than with it off (p<0.05). One subject had significantly more accurate and more clustered responses with the system off than on and one subject showed no significant difference between conditions. In the door orientation and mobility task, nine subjects had better performance with the system on (smaller mean distance away from the target door over all trials), two subjects had better performance with the system off, and one subject showed no difference. Pooling data across all 12 subjects, there was significantly better performance with the system on than with the system off (paired t-test, p<0.05).
The Argus II retinal prosthesis improved the ability of blind subjects to find and indicate the position of an object on a computer screen and also to find and walk to the position of a door in a room. These results suggest that the Argus II system may enable blind subjects to locate and interact with objects in their daily lives, consistent with subjects' self-reports.
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