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Christopher Phillips, Steven Bierer, Chris Kaneko, Leo Ling, Kaibao Nie, Amy Nowack, Jay Rubinstein, Sarah Shepherd, James O. Phillips; Longitudinal Efficacy Of A Prosthesis Designed To Treat Pathological Nystagmus And Oscillopsia Resulting From Head Motion. Invest. Ophthalmol. Vis. Sci. 2012;53(14):518.
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We have developed a prosthesis that stimulates the ampullary nerves of the vestibular labyrinth to stabilize images on the retina in patients who have nystagmus or absent vestibulo-ocular reflex function. The device, based on a Nucleus Freedom cochlear implant, can deliver electrical stimulation based on head motion, eye motion, or a preprogrammed sequence. In order to utilize this strategy to treat pathological conditions in human subjects, we need to understand the long-term viability of the fully implanted device and electrode array.
In 6 rhesus monkeys, we followed the eye movements in response to controlled electrical stimulation over periods of up to 15 months to see if there was any change in the eye movement behavior elicited by the stimulation over time. Typical stimulation parameters were 2s constant frequency trains of biphasic pulses of constant current, recorded at the beginning of an experimental session. In addition, we recorded the impedance of the electrodes at several intervals, and we performed behavioral and neural recording experiments with varied stimulation from the device 3-5 times per week.
In response to lateral canal stimulation, two animals showed increased horizontal slow phase eye velocity over time, while three animals showed decreased velocity, and one animal showed no change. In animals where there were multiple canals implanted, the changes in the slow phase velocity during stimulation were canal independent. In one animal, longitudinal data was obtained at several frequencies and currents of stimulation. The relationship between stimulation frequency and/or current and slow phase velocity was unchanged over time. The observed longitudinal changes were not correlated with changes in longitudinally measured electrode impedance.
Longitudinal recording of slow phase eye velocity resulting from stimulation by a vestibular prosthesis suggests that responses are maintained over the course of up to 15 months, but the quality of response may change with time. The factors producing such changes are unknown, but do not appear to be related to the impedance of the stimulating electrodes.
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