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G. Richard, M. Keserue, R. Hornig, N. Post, O. Zeitz; Long-Term Stability of Stimulation Thresholds Obtained From a Human Patient With a Prototype of an Epiretinal Retina Prosthesis. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4580.
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Retinal prostheses are one of the most promising approaches to restore at least a part of the visual acuity of a patient suffering from diseases which are characterized by photoreceptor degeneration (Retinitis pigmentosa, CRD, Choroideremia). Stimulation thresholds for eliciting visual perceptions in one patient were recorded with a chronic implanted retina stimulator for 4 months.
The prototype of the epiretinal stimulator (IMI Intelligent Medical Implants GmbH, Bonn, Germany) was implanted in a patient who was blind due to retinitis pigmentosa. The implant consisted of a flexible film equipped with an electrode array which was attached to the retina by a retina tack. The array is connected to an assembled stimulation unit sutured on the sclera under the Tenon’s capsule. Data and energy were transmitted to this unit wirelessly. Thresholds were determined by applying stimuli with a charge between 0 and 122nC corresponding to 8 different levels in randomized order. Each level was tested five times during each run. The patient’s response ("perception"/ "no perception") to a stimulation was recorded in a two alternative forced choice test. The stimulation threshold was calculated for each run.
Twenty-three stimulation runs were conducted with one electrode over a period of four months. In 18 runs the patient responded with a correct positive at the two maximal stimulation intensities, while in five runs false negative answers were given with maximum stimulation intensity. The threshold was in a range of between 8.0 and 35.9nC with a mean of 17.4nC (SD ±7.9).
The stated method is appropriate to follow changes in threshold over time. The data shows stability of thresholds over four months. The relatively low thresholds measured are very encouraging for the development of stimulation strategies.
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