97th DOG Annual Meeting 1999



L. Hesse1, T. Schanze2, B. Nebeling1, M. Wilms2, M. Eger2

For restoring a simple basic visual perception in patients that are blind due to photoreceptor loss ganglion cells should be stimulated by epiretinal electrodes. Therefore plane platin microelectrodes embedded in thin polyimide film were developed.

Methods: After removal of the lens and the vitreous body a thin film of 2 x 4 parallel arranged microelectrodes were implanted through a corneal incision in the cat eye (n=4). The exterior part of the microelectrode film was directed through the forehead which allowed fixation of the micro plug at the head fixation bolt. For intraocular placement of the microelectrodes microsurgical instruments were used. The microelectrodes were pressed at the retinal surface by bending the microelectrode film. In 2 eyes the tip of the electrodes were additionally glued to the retina using cyanoacrylate. Stimulation experiments were performed between 1 to 14 days after implantation. Success of stimulation was controlled by recording epidural and intracortical activities (area 17/18). Microelectrodes were removed at least 3 weeks after implantation.

Results: Intraocular inflammation or retinal detachment were not observed after implantation of the microelectrode film. Without additional fixation the tip of the microelectrodes dislocated spontaneously. Threshold of electrical stimulation varied between 50 and 100 µA which was tenfold increased compared to needle electrodes used in prior experiments.

Conclusions: Intraocular implanted microelectrodes made from polyimide were well tolerated. However, the planare configuration of the microelectrodes required higher current pulses for stimulation which may be explained by inadequate contact to the retinal surface. An additional fixation of the electrodes is essential.

(Supported by BMBF, grant no. 01 IN 501 F).

1 Augenklinik, Philipps-Universit├Ąt, Robert-Koch-Str. 4, D-35033 Marburg
2 AG Neurophysik, Philipps-Universit├Ąt, Renthof 7, 35032 Marburg