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Abstract
Vitreoretinal Symposium Marburg - Frankfurt 1999
SUBRETINAL MICROPHOTODIODES - UPDATE E. Zrenner, H. Haemmerle, K. Miliczek, A. Stett, S. Weiss Univ. Eye Hospital, Dept. II, Schleichstr. 12-16, 72076 Tübingen During the past 4 years, a number of problems regarding the development of subretinal microphotodiodes as a visual prosthesis could be solved. However, a lot of work still has to be done, and new questions arose. Longterm biostability has to be improved and an external power supply is actually developed. An overview will be given about the present state of this research project. It is necessary for the successful development of a subretinal implantable visual prosthesis to understand the basic principles of electrical stimulation of the retina. In-vitro-experiments showed that subretinal electrical stimulation evokes correlated ganglion cell activity even in highly degenerated RCS rat retinas. In rabbit experiments, a flexible electrode array was implanted subretinally. Electrically evoked cortical potentials (EECPs) were recorded after a voltage or current pulse was applied to the retina. Waveform and size of the EECPs varied with the amount of transferred charge and the stimulation mode (bipolar vs. monopolar). Design parameters for the development of an active subretinally implantable visual prosthesis can be extracted from the results obtained with the degenerated retinas in vitro. The successful recording of EECPs elicited with subretinally applied electrical stimuli demonstrates that the subretinal approach of a visual prosthesis is very promising. Back |