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L. J. Johnson, D. Scribner, P. Skeath, R. Jensen, J. Rizzo, D. Ilg, R. Klein, F. K. Perkins; Pre-Clinical Testing, Voltage Recording and Retinal Contact Imaging With a 3200 Electrode Retinal Stimulation Array. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2560.
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The NRL retinal stimulator with 80 x 40 individual electrode areas (pixels) has three components; the curved microwire glass electrode, the microelectronic multiplexer, and the drive electronics. The device is designed to be placed against the retina during acute 1-hour tests -the device is connected to the drive electronics by a microcable the passes through a small slit in the sclera. Our recent efforts have focused on imaging retinal contact, characterizing the current delivery and voltage recording capabilities of the multiplexer, and performing pre-clinical tests.
The NRL retinal prosthesis can readout the voltage at each electrode in the array. When a uniform current image is presented, this readout provides an image of the impedance map of the device surface. This impedance map indicates the contact of the device with the retina. Electrical current as a function of both image intensity and biphasic pulse amplitude was characterized during saline immersion. Pre-clinical tests were performed at the Boston VAMC to evaluate the stimulation characteristics of the device.
The change in the output image, from the device, was correlated with the applied impedance. The output image was sensitive to impedances ranging from 5k to 1200K Ohms. The primary control of the output current is the video image intensity. The relationship between the output current and the video image intensity is quadratic. The biphasic pulse acts linearly upon the output current. The typical NRL device outputs currents up to 3 microamps per electrode, for a charge density up to 500 microCoulombs/cm2. The NRL device was capable of stimulating isolate retina.
The NRL stimulator array has the added advantage of real-time imaging of the degree of contact between the device and the retina. The microelectronic multiplexer current delivery performance matched electronic design predictions closely. Pre-clinical tests indicated that the 3200 electrode NRL stimulator is capable of stimulating the retina.
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