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Leonid Yanovitz, Dorit Raz-Prag, Keren-Or Eden, Rahul Saini, Yael Hanein, Ra‘anan Gefen; Retinal responses evoked and recorded with 3D electrodes designated for a novel prosthetic device. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1808.
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© ARVO (1962-2015); The Authors (2016-present)
The Nano-Retina (NR) retinal prosthetic device transforms the visible signal into an electrical signal that is transduced to the retina via an array of needle electrodes. The purpose of this work was to stimulate the retina via the NR electrodes, to characterize the retinal responses that are obtained from them and to compare these results to retinal responses obtained with a commercial flat Multi-Electrode Array (MEA).
The embryonic chick retina was used as a model as it allows detection of anterograde and retrograde responses, a clear distinction between direct and indirect responses and also shares some features with the degenerating retina. Retinas were harvested at E14 and mounted, ganglion cell down, on an array of NR silicon needle electrodes coated with Titanium Nitride (TiN), or a commercial Multi-Channel Systems (MCS) MEA of flat TiN electrodes. The retinas were kept at physiological conditions throughout the experiment. Retinas were electrically stimulated through one electrode each time with charge-balanced bi-phasic current stimulation. Signals were amplified (1,200X) and digitized using an MCS MEA amplifier.
Spontaneous retinal waves were detected with both types of MEA and signal to noise ratios were equivalent. Charge threshold for retinal activation in the chick retina was 1nC at minimum with the MCS MEA (electrode area ~700um2), which corresponds with the activation threshold described previously for the mouse retina. Charge threshold with the NR electrodes was lower and stood at <0.5nC (effective electrode area ~1000um2). Subsequently, the retinal area that was evoked appears smaller with the NR electrodes relative to the flat MEA.
The lower threshold obtained with the NR electrodes suggests that their unique design makes them advantageous for retinal activation. The 3D penetrating needles that allow close proximity of electrode tips to the target activation site and the low charge required to trigger a response are key features for obtaining high resolution in a prosthetic device.
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