[Electrical stimulation of the visual system. From empirical approach to visual prostheses].

The investigation of the influence of electrical stimulation on the visual system can be sub-divided into empirical, diagnostic and therapeutic phases of development. The first electrical stimulations of the visual system in animals dating back to the eighteenth century represent empirical approaches well before knowledge on the principles of bioelectrical nerve activity was available. Despite this lack of understanding, attempts were made at that time to treat blind people by electrical stimulation. More than 100 years later, with the advancement of technology and knowledge on nerve function, attempts were made to establish various methods of electrical stimulation for the diagnosis of different diseases of the visual system. For more than 30 years attempts to develop electrical devices have been made to by-pass defects of the visual system and to restore basic orientation. Presently nine different groups world-wide are focusing on retinal, optic or cortical implants. A short review on the historical use of electrical stimulation and new therapeutical attempts are given in this paper.