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Thomas Anthony Flores, Xin Lei, Tiffany Wanshing Huang, Henri Lorach, Roopa Dalal, Theodore Kamins, Keith Mathieson, Daniel V Palanker; Optimization of pillar electrodes in subretinal prosthesis for enhanced proximity to target neurons. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4200. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
High-resolution visual prostheses require dense stimulating arrays with highly localized current injection to convey high fidelity visual information to the remaining retinal neurons. Reducing the electrode to target cell distance is expected to decrease stimulation thresholds and electrical cross-talk, enabling higher spatial resolution. In this study, we test the integration of pillar electrodes with retinal tissue following implantation in the subretinal space and model the electric field produced by high-density subretinal arrays.
Silicon arrays were fabricated with cylindrical pillars 5, 10, and 20um in height. Pillars were 6, 10, and 14um in diameter, with 40, 55, and 70um pitch, respectively. Two devices of each geometry and two devices with no pillars (control) were implanted into the subretinal space in rats with retinal degeneration (RCS). Retinal integration with the implants was assessed at 6 weeks post implantation using confocal microscopy of immunostained whole-mount retinas and histological sections. Electric fields were modeled using COMSOL Multiphysics and converted to retinal response using a threshold-mediated model based on the measured cellular proximity to the electrode surface.
All sizes of the pillar electrodes integrated well with the retina without significant fibrosis. Pillars of 10um in height penetrated to the middle of INL, while 20um pillars penetrated to the top of the INL. Modeling the retinal response indicated optimal pillar placement at the bottom of the INL, while electrode penetration into the INL reduced stimulation of the cells located below the electrode surface due to reversed orientation of the electric current.
Pillar electrodes in the subretinal space reduce the distance from the electrode surface to the INL compared with flat arrays. Careful atraumatic implantation results in excellent integration of the implant with the retinal tissue with no significant fibrosis. Electrode penetration into the INL may reduce stimulation efficacy due to reversal of the electric current below the plane of the electrode surface. Optimal electrode height depends on the thickness of the subretinal debris layer separating the implant from the INL. Future studies with active devices in-vivo will quantify the difference in stimulation thresholds, contrast sensitivity, and spatial resolution between implants with flat and 3-D electrodes.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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