In order to deliver sufficient phosphene quantities to convey effective vision in a prosthesis device, simultaneous stimuli is necessary. We present in vitro experimental results of the current distribution between stimulation sites during simultaneous stimulation of platinum electrodes immersed in physiological saline. Stimuli were delivered using circuitry that utilizes (a) current source only, (b) current sink only, and (c) the combination of a balanced current source and current sink, to deliver and recover balanced charge at each stimulation site. The results from these experiments support our decision to implement balanced combined current source and current sink circuitry in an application specific integrated circuit (ASIC).
The loss of the ability to blink is considered the most severe consequence of facial nerve paralysis. Surgical techniques and implantable technologies continue to be developed to reanimate the eye; however, few analyse the full movement of blink when evaluating success. Here, we describe a method of taking high-quality, and high-speed video recordings of the eye, to non-invasively extract meaningful data about the dynamic movement of blinking. This can then be used to assess the effectiveness of a new technology in mimicking the natural movement. The tool was validated on humans (N=2, authors) before testing on an ovine recording (N=1), to confirm the cross-species utility of the tool, for use during preclinical development of technologies. It was found to be accurate and comprehensive, able to give insights on blinking in both human and ovine cases.
Therapeutic, electronic medical implants used in auditory, visual, functional, and behavioral neuroprosthesis often are required to maintain their function for the remaining lifetime of the implantee. This requirement presents a substantial engineering obstacle that has previously limited the practical upper quantity of electrodes, or other signal carrying channels such devices may possess. Hermetic encapsulation of any implanted electronics and the tendency of this encapsulation to leak is a well-known problem for biomedical engineers. Each "hard-wired" signal required by, or elicited from, the implant must pass through the encapsulation without breaching hermeticity. The present paper describes a method of fabrication of hermetic feedthoughs (leak < 2 × 10-9 std cc He/s) comprising materials with superior biological compatibility characteristics and able to accommodate relatively high numbers of signal carrying channels relative to existing methods, while allowing this to occur within small areas.
Microelectrode arrays for a stimulating retinal prosthesis were fabricated from laser etched platinum (Pt) foil encased in silicone. A total of 12 arrays were fabricated to test performance in saline. Hexagonal arrangements (N=6) with multiple (6) return electrodes, as well as paired electrodes (N=6) with single returns were constructed. Electron microscopy of the electrode's surfaces was performed. Cyclic voltammetry was performed on all electrodes to measure the real surface area. The electrodes were submerged in saline in an incubator and biphasic pulses of plusmn162 muA and plusmn280 muA for 400 mus were applied at a rate of 67.1 Hz for 12 weeks. Microscopy and cyclic voltammetry were repeated and changes to the electrode's surfaces were observed both by visual inspection of the micrographs and analysis of the cyclic voltammetry curves. Extensive corrosion to those electrodes subjected to the higher current suggests a charge injection limit of less than the original 350 muC/cm 2 estimate. Analysis of different corrosion levels between the hexagonal and paired arrangements show that a hexagonally arranged electrode array, with multiple return electrodes, allows a greater stimulation current to be used without reaching the charge injection limit of the electrodes.
By way of extracellular, stimulating electrodes, electronic vision prosthesis aims to render discrete light spots - so-called phosphenes - in the visual field, thereby providing a phosphene image serving as a rudimentary remediation of profound blindness. It is proposed that a digital camera, or some other photosensitive array, captures frames, the frames be analyzed, and phosphenes be actuated accordingly. We present a numerical experiment wherein we observed the phosphene image in response to a set of stimuli for various image analysis schemes. We used the mutual-information function to quantify the efficacy of analysis schemes; the function penalizes a scheme for introducing redundancy to the phosphene image, while accounting for the probability of each stimulus. We demonstrate an effective scheme involving Laplacian of Gaussian (/spl nabla/2G) kernels geometrically transformed in accordance with phosphene layout. Further, we propose adapting the kernels comprising a scheme in accordance with photosensor movement.
This chapter contains sections titled: Introduction Retinal Neuroprosthesis Review Biology Inspires Design Parallel Concurrent Stimulation in Retina Critical Areas for Research and Development Conclusions References
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