Scientists have been working on developing retina prostheses for more than twenty years now. Research has been conducted particularly intensively in Germany, where scientists and patients have worked in tandem and have succeeded in obtaining government funding. "Back then we didn't want high-tech just for space and defence programmes but finally high-tech for people as well", Professor Rolf Eckmiller, a neuro-informatics specialist at the University of Bonn and a pioneer in the field, recalls.
This investment is now bearing fruit. The German research consortiums lead the field in this area of research. Three of the four research teams who presented their findings in Bonn are from Germany.
As the presentations showed, all the electronic retina prostheses convey visual impressions, so-called phosphenes. Patients participating in a United States study were able to distinguish light and dark and to register movement and the presence of larger objects. In addition, early reports from a project being conducted by a German research group led by Profesor Eberhart Zrenner at the University of Tübingen indicate that restoring visually impaired patients' ability to read is not just wishful thinking. Some patients are able to read letters if these are eight centimetres high.
"We're in the final run-up", explained Professor Peter Walter from the University Eye Clinic in Aachen. Professor Walter is scientific director of the symposium "Artificial Vision". "The final studies prior to market launch have begun or are set to begin", he stated in his latest progress report. These studies are designed to test the long-term tolerability of the retina implants and their benefits in everyday life. The manufacturers expect the implants to be approved in 2011.
Naturally, there is a lot of interest among patients in the new products. "Compared with the study we conducted ten years ago, patients now have a much clearer idea of what they expect from retina prostheses", stated Helma Gusseck, chairperson of the Stiftung Retina-Implantat - Retina Implant Foundation. Helma Gusseck, who also chairs the Pro Retina Stiftung, suffers herself from Retinitis pigmentosa, a degenerative retina condition and can now only distinguish between light and dark. For her the research findings are a relief: "You can, so to speak, go blind without worrying about it, because you know that the systems will soon be ready and we therefore have an option."
Nevertheless, this is really only the beginning. "What we're seeing is different systems racing to compete", stated Peter Walter. In one of the systems - the sub-retinal implant - the chip is implanted under a layer of nerve cells in the retina. There, like the photoreceptors in the retina, it receives light impulses, converts these into electrical signals and transmits them to the nerve cells of the retina. The retina prosthesis developed by Professor Zrenner's team in Tübingen and that developed by a United States team led by Joe Rizzo and Shawn Kelly at the Boston Implant Project in Cambridge, Massachusetts, work according to the same principle.
In the case of the so-called epiretinal implant the chip is fixed to the upper-most layer of nerve cells. There it receives data from a small camera installed in glasses worn by the patient and likewise converts these into impulses for the nerve cells. This is the principle employed by the retina prostheses developed by the two other German research teams. One of the systems - IRIS - was developed by the Bonn company IMI, the other - EPIRET3 - by a research consortium that includes scientists from the RWTH Aachen and the Fraunhofer Institut für Mikroelektronische Schaltungen und Systeme - Institute for Microelectronic Circuits and Systems - and doctors at the University Eye Clinic Aachen led by Peter Walter.
Alongside these various systems, which also differ from one another in a number of other details, the next generation of retina prostheses is already in the pipeline in laboratories around the world. Engineers, computer science specialists, biologists and doctors are pooling their knowledge to evolve new strategies for linking electronic devices and nervous systems.
Teams of researchers in Switzerland and Japan, for example, are developing systems in which the chip is no longer implanted in the eye but outside it on the dermis that protects the eyeball in the socket. Only the electrodes that stimulate the nerve cells in the retina are inserted inside the eye through a small incision. Chinese researchers are developing retina prostheses that, instead of stimulating the nerve cells of the retina, stimulate the optic nerve directly. And an American team is trying to activate the visual cortex in the brain directly. At this point it is not clear when, if ever, any of these systems will be ready for patient trials - currently they are still at the experimentation stage.
Much interest has also been shown in projects to use other communication signals between nerve cells. Australian and American scientists are working on retina prostheses that produce biochemical impulses instead of electrical ones. The idea is for the retina prostheses to release neurotransmitters according to spatially and temporally controlled patterns and thus stimulate the nerve cells.
The question remains whether retina prostheses will eventually be able to register shapes, as Rolf Eckmiller hopes they will. "To do this will require a retina prosthesis capable of learning and that is able to produce a kind of melody of impulses that can be recognized by the brain and classified as a particular shape, like a cup." Rolf Eckmiller is convinced that the complex central vision system - which occupies a third of the cerebral cortex - can only register a shape if the right "melody" is transmitted via a sufficiently large number of cells.