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Milan Djilas, Ryad Benosman, Philippe Bergonzo, Christoph Posch, Jose Sahel, Serge Picaud; Reducing the Number of Stimulators and Electrical Tracks in High-Resolution Visual Prostheses. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1064. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal diseases such as RP and AMD cause photoreceptor degeneration while other cell layers partially remain. Retinal prostheses restore useful vision by activating these cells. The NxN electrode matrix and stimulators are coupled with N2 electrical tracks. With the increase of pixel resolution, this inter-connection becomes difficult to fabricate. The foil also becomes more rigid, making the implantation surgery more challenging. Here we propose an alternative electrode design and connectivity layout that significantly reduces the required number of metal tracks and stimulators.
The proposed layout is shown on Figure 1. To stimulate a particular pixel, segments from one row, one column and two diagonals containing that pixel are activated simultaneously. To excite only the tissue at the target pixel, the stimulation intensity of each active segment is kept below threshold, whereas the intensity of simultaneous activation of four active segments at the target pixel is above threshold.
The proposed layout requires a total of 6(N-1) electrical tracks and only 4 stimulators (1 for row, 1 for column, and 2 for diagonals) regardless of implant resolution. One additional track is needed for a common counter-electrode. Finite-element method simulations clearly confirm significantly higher stimulation intensity at the target pixel compared to other pixels stimulated with 4x lower intensity. This range should be sufficient to activate only the former.
The proposed strategy requires 6N-5 tracks and 4 stimulators, compared to N2+1 tracks and N2 stimulators in the standard one-track-per-electrode layout. The downside of such an approach is that only a single pixel at a time can be activated. This would however not be a limiting factor if asynchronous image acquisition is implemented. Future work includes experimental validation of the proposed strategy.
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