Retinal implants: the ophthalmologist's viewpoint

Devices for electrical stimulation of retinal neurons were implanted into rabbit eyes using modern vitreoretinal microsurgical procedures. Biocompatibility was tested in-vivo clinically and by means of electrophysiology. Visual reactions to electrical stimulation of the inner retinal layers were recorded by means of electrical evoked cortical potentials. The devices which had been tested proved their biocompatibility in the rabbit during a 6-month follow-up period. With these devices cortical evoked potentials could be elicited using biphasic mono- or bipolar current pulse trains. Threshold charges of 1-3 nC/pulse/phase could be found in ideal experiments. Ophthalmological problems of the technical approaches of a retinal prosthesis are discussed in comparison with biological approaches as gene therapy or retina transplantation for the treatment of retinal degenerations.