Delivery of information and power to the implant, integration of the electrode array with the retina, and safety of chronic stimulation

Abstract

The fundamental function of a visual prosthesis is to deliver information about a patient's surroundings to his/her neurons, usually via patterned electronic stimulation. In addition to transmitting visual information from the outside world to the implanted stimulating array, visual prostheses must also pass the electrical power necessary for such stimulation from the external world to the intraocular electrode array. The first section of this chapter reviews three common methods for achieving this data and power transfer: direct wireline connections (suitable for research studies), inductively coupled coils, and photodiode-based optical systems which utilize the natural optics of the eye. Once the data and power has been received, retinal prostheses must effectively deliver stimulation currents to surviving retinal neurons. This necessitates an understanding of the electrode/retina interface. The second section of this chapter is a histological description of this interface for the case of subretinal implants, investigating the tissue response to flat implants coated with different materials. Several three-dimensional geometries are also described and evaluated to decrease the implant-neuron distance. Finally, stimulation currents must not damage the stimulated neurons. The third section of this chapter describes measurements and scaling laws associated with tissue damage from electric currents. Damage thresholds are found to be approximately 50-100 times stimulation thresholds. © 2011 Springer Science+Business Media, LLC.