97th DOG Annual Meeting 1999
SUBRETINAL ELECTRICAL STIMULATION OF INTACT AND DEGENERATED RETINAS
E. Zrenner1, S. Weiss1, A. Stett2
Background: It is necessary for the successful development of a subretinal implantable visual prosthesis to understand the basic principles of electrical stimulation of the retina. The aim of our study was to find stimulation parameters that are suitable for longterm electrical stimulation of distal retinal neurons.
Methods: A) in-vitro experiments: Degenerated retinas of RCS-rats were positionrd on to a microelectrode array (MEA). Voltage and current pulses were applied to the distal side of the retina and stimulus correlated ganglion cell activity was recorded. B) in-vivo experiments: A flexible electrode array was implanted subretinally in rabbit eyes. Electrically evoked cortical potentials (EECPs) were recorded after a voltage or current pulse was applied to the retina.
Results: in-vitro experiments: Subretinal electrical stimulation evoked correlated ganglion cell activity even in highly degenerated RCS rat retinas. A charge density of 100-1000µC/cm2 was required to elicit threshold responses. The spatial resolution was 100-200µm. In-vivo experiments: EECPs could be elicited in rabbits with either voltage or current pulses applied to the proximal side of the retina. Waveform and size of the EECPs varied with the amount of transferred charge and the stimulation mode (bipolar vs. monopolar).
Discussion: 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.
1University Eye Hospital, Dept. II, Schleichstr. 12-16, 72076 Tübingen
2Natural and Med. Sciences Institute, Markwiesenstr. 55, 72770 Reutlingen