Artificial Vision Project　Development of Surgical Techniques for Implantaion/Assessment of Biocompatibility

Department of Ophthalmology,Osaka University Medical School

Several groups in Europe and the United States have been trying to develop.an electrode array to implant over or under the retina to stimulate the retina. At the same time, our group has formulated the suprachoroidal transretinal stimulation system (STS system) in which the retina is stimulated with transretinal current from the outside of the retina (sclera or choroid) to the inside of the retina without touching the retina. The effectiveness of this system was confirmed in experiments using rats. It is now very important to examine safe methods to implant the electrodes, and to determine the safety and biocompatible of the materials on middle size animals whose eyes are as large as humans.
Our group at the Department of Ophthalmology in Osaka University Medical School is chiefly in charge of developing safe and effective operative procedures to implant the electrodes into patients' eyes and examining the design and the compatibility of the electrodes and the ancillary equipment for the STS system. The objects of our studies are rabbits and miniature pigs. The results from rabbits are introduced below. We were able to implant the electrode array successfully_into the space between the choroid and sclera (Figure lower left). without major complications. The implanted electrode can be seen through the vessels of the retina and choroid (Arrows, lower right). When the transretinal electrical pulses were applied, electrically evoked responses could be recorded at the visual cortex. These results mean that the retina was stimulated with the current and the signal was conducted to the visual cortex. We are also examining the effect of long term implantation in the rabbits and miniature pigs and examining the biocompatibility and the tolerance. We are now aiming to achieve a safer and more effective visual prosthesis.

Kyorin Eye Center,Kyorin University School of Medicine

It is important to identify the optimal technique of electrode (prosthetic device) implantation, the optimal site of implantation, and the complications which can develop after electrode implantation around the retina. Thus, it is essential to analyze the changes in the retina that can occur due to electrical stimulation, and to perform histological examinations to determine the biocompatibility of the implanted electrodes with the goal of developing an operative procedure with minimal stress, i.e., to minimize/prevent retinal injury, retinal detachment, massive bleeding, postoperative inflammatory reactions, proliferative changes,
and other complications.
In contrast to research on retinal prosthesis currently performed by several groups in Western countries, we are investigating artificial vision based on suprachoroidal transretinal stimulation. Each approach has its own advantages and disadvantages. It has not yet been determined which of them might be more useful in practice. Implanted electrodes may induce not only retinal detachments, but also　inflammatory reactions, edema, migration of pigmented epithelial cells, and　proliferative reactions due to activation. In addition, there are still many　unresolved questions about the host's responses to the foreign material.
We have examined the effects of vitreous surgical techniques needed for electrode implantation on the tissues around the retina, using the eyes of rabbits and pigs. In animals in which a chip (a model of the electrodes) was kept implanted above or below the retina for short periods of time, we have found by macroscopic, light microscopic, and electron microscopic examinations that the host's responses to the chip were mild, but the chipinsertion site lost stability. We are now in the process of investigating the changes in the tissues around stimulating electrodes implanted into the suprachoroidal space.