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G. Richard, M. Keserue, M. Feucht, N. Post, R. Hornig; Visual Perception After Long-Term Implantation of a Retinal Implant. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1786.
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to conduct a human long-term implantation study with a newly developed retinal implant to verify new surgical procedures and to obtain stimulation results from a permanently attached electrode array in patients suffering from retinitis pigmentosa
4 patients (56 to 66 years) with visual acuity ranging from no light perception to hand movement were provided with an epi-retinal device (IMI Intelligent Medical Implants). The wireless powered implant containing energy receiving coil was extraocularly attached to the sclera. The flexible implant tongue containing a 49 electrode array was inserted into the eye by conducting a sclerotomy in a scleral pocket and was attached using a silicon ring to a titanium tack which had been placed in the sclera. Regular follow-up examinations took place to review the eye with OCT images, fluorescence; ICG angiographies and funduscopies. Up to 20 stimulation sessions were carried out with the patients over a 12 month period. Single electrodes or electrode patterns were activated with pulse trains transmitted into the eye via an infrared connection. Individual thresholds and the pattern recognition were tested.
The surgical results revealed that the implant was well tolerated in the eye. The imaging procedures indicated good electrode contact to the retinal tissue with no side effects. Perceptual thresholds obtained with different patients and different electrodes were dependent on the charge applied. The average threshold obtained from a Weibull fit resulted in 25.3 +/-7 nC and is considerably lower than the result obtained in a previous study involving acute stimulation with the same patients. Simple patterns (vertical / horizontal bar, a cross) originated via activation of appropriate electrodes were distinguished by the patients. Visual percepts depend on amplitude levels and electrode localisation. The time dependent of visualpercept is demonstrated.
The Retina Stimulator is biocompatible and stimulation indicated that the device may be suitable for longer term use in human eyes. Retintopic perceptions can be elicited via activation of geographically correlated electrodes on the array. The relatively low thresholds measured are encouraging for the development of stimulation strategies.
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