NSF/FDA SIR: Bioimpedance of stimulating electrodes for the safe placement of retinal implants

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PI: Peixoto, Nathalia LProposal: 1445684Title: Bioimpedance of stimulating electrodes for the safe placement of retinal implantsSignificanceThis project may provide society are a better understanding of the design issues that cause a loss of effectiveness of retinal stimulus electrodes in blind subjects. In retinal implants, the distance between the stimulating electrode and the surface of the retina is a critical variable for determining perceptual thresholds and for implant safety in general. When the electrode is too far from the target ganglion cells, the current density achieved in the retina is low, in part due to current spreading through the vitreous humour, thus raising the perceptual threshold and therefore decreasing spatial resolution. If, on the other hand, the electrode touches the retina, mechanical damage can be expected. There is therefore a need to determine the distance from the electrode to the retina in situ. The PI proposes to investigate methods to reliably measure electrode proximity to the retina, with the objective of establishing techniques which are readily translatable to current technology.Technical DescriptionRetinal prostheses for the blind are in clinical trials worldwide, including the FDA-approved Argus II prosthesis. Each retinal prosthesis attempts to position stimulus electrode arrays in close proximity to the retina in order to effectively activate the remaining retinal neural circuitry. Retinal activation by electrodes in different locations on the retinal surface are not all equivalent. Stimulus pulses can be markedly attenuated by resistive and capacitive barriers in the eyewall, which in some cases could prevent effective activation of the retinal tissue. Here we plan to investigate the impedance correlates of mechanical damage to the inner retina by the stimulus electrodes, as well as electrically-mediated damage (due to high charge density). The main objective of this project is to determine safety throughout the period when the implant is used, in situ, leveraging currently available technology for retinal implants.