Electronic visual prostheses

BACKGROUND: Currently, no treatment is available for progressive retinal dystrophies. The fabrication of an implantable visual prosthesis seems to be possible now as a result of advances in the fabrication of extremely small micro-systems and their encapsulation in biocompatible materials. MATERIALS AND METHODS: The development of implantable visual prostheses is based on the fabrication of remotely controlled microelectrode arrays which have to be implanted in different target regions of the visual system. Prototypes of such systems have already been implanted in animal experiments and also in pilot trials in humans. RESULTS: Four concepts are pursued: 1. epiretinal implant -- fixation onto the inner retinal surface; 2. subretinal implant -- implantation within the subretinal space; 3. optic nerve stimulator -- cuff electrode placed around the optic nerve; 4. cortical prosthesis -- implantation of surface electrodes in the region of the visual cortex. All these concepts have already been applied in pilot trials in humans. The results show some promising visual perception. CONCLUSIONS: The use of implantable electronic visual prostheses will become a possible option in the treatment of currently untreatable retinal dystrophies. Further basic research initiatives are necessary as well as further human trials to characterize the stimulation parameters and to improve the currently available devices.