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Thomas Z. Lauritzen, Devyani Nanduri, Jim Weiland, Jessy D. Dorn, Kelly McClure, Robert Greenberg, Argus II Study Group; Inter-electrode Discriminability Correlates With Spatial Visual Performance In ArgusTM II Subjects. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4927.
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To estimate the spatial resolution of Argus II subjects and its correlation with performance in spatial visual tasks.
The Argus II retinal prosthesis system includes a 10 x 6 electrode array implanted epiretinally, a tiny video camera mounted on a pair of sunglasses, and a small external computer that processes the video and determines the stimulation current of each electrode in real time. Single electrodes and pairs of electrodes were stimulated at current levels twice the threshold for perception in randomized trials (five repeats per pattern). After each stimulation subjects were asked to draw their visual perception on a touch screen monitor. Subjects had no knowledge of the stimuli or given any feedback on their responses. The number of perceived phosphenes for each trial was determined based on the non-overlapping drawing segments of the drawings. The phosphene discriminability of electrodes as a function of inter-electrode distance was correlated with their performance in a grating visual acuity task, in which the subject identified the orientation of gratings at different spatial frequencies in a 4 AFC paradigm.
The phosphene discriminability increases with inter-electrode distance, but the discriminability for individual pairs of electrodes depends on several factors, as the distance between the electrode and retina. There is a strong correlation between the two point resolution and the grating visual acuity task, the higher the two point resolution, the better the visual acuity.
The results demonstrate a correlation between basic visual stimulus discriminability and visual performance in Argus II subjects. To our knowledge, this is the first quantitative assessment of visual performance and basic electrode array properties in a larger study group.
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