A team in Cork hopes to replace lost vision by implanting microchips in people's eyes. Dick Ahlstrom reports
Electronics specialists and eye surgeons in Cork have joined forces to find ways of reversing progressive blindness. A new research project funded by the Irish charity Fighting Blindness hopes to use microchips that work as virtual eyes, linking with cells in the optic nerve to return some level of visual response.
Retinitis pigmentosa and age- related macular degeneration are the two leading causes of progressive blindness. Both involve the loss of rods and cones, two cell types in the retina that are essential for vision.
Research groups around the world are attempting to develop electronic replacements for the rods and cones, according to Dr Anthony Morrissey of the biomedical microsystems group at the National Microelectronics Research Centre, part of University College Cork. The idea is to develop microelectrode arrays that can send signals into the optic nerve, replacing those sent by the rods and cones. "The microelectrode array would do the job of those cells."
It is still unrealistic to suggest that anything like proper sight might be achieved, says Morrissey. The systems could, however, give back enough vision to restore a sense of night and day, something Fighting Blindness says would be a major advance. In time, as the devices improved, their users might be able to identify large objects, such as cars or open doors, says Morrissey.
The centre has decades of experience of developing advanced microelectronic devices. The biomedical microsystems group was set up about four years ago to look at implants and biosensors. It involves a team of 12-14 researchers, including electronic engineers, chemists, biochemists, microbiologists and physicists.
Fighting Blindness decided to help the centre get involved in world research efforts in this area. Its three-year grant is "like a foot-in-the-door project", says Morrissey. It allows the centre's team to apply its expertise to the challenge.
He and colleague John Alderman joined with surgeons Prof Philip Cleary and Dr Hossein Ameri of Cork University Hospital to develop devices and surgical techniques to provide the electronic vision.
The technical and the surgical challenges are enormous, says Morrissey. "The surgeons say attaching a chip to the retina is like trying to attach a concrete block to a wet piece of tissue paper." The devices must be very small and very thin but able to accept a signal, then redistribute it across a microelectrode array to produce "vision" that can be interpreted by the brain.
"We have started to move towards flexible implants based on polyimide film," says Morrissey. "It is tricky to make them small and flexible enough, and one of the major issues is getting them working."
The team is building a polymer film complete with electrodes - squares of platinum - that can be pressed against nerve cells. This can be built into layers, creating more complicated circuitry. To this can be added microcoils, which allow low voltages to be induced in the circuits, and a "microplexer" that can get more information out of a single incoming signal.
The centre's team is also modelling these devices, simulating the circuitry and assessing how it might perform when in position. In addition, it is studying the effect an implant has on eye tissue and the problems it can cause.
The hospital team is evaluating the best surgical approach - "epiretinal" placement, or putting the chip on the surface of the retina, or "subretinal" placement, or putting it just under the retinal tissues. "Each has its own advantages and disadvantages," says Morrissey, but the UCC team prefers subretinal. "It is less difficult to slot an implant in behind the retina than having to tack it onto the front."
The Cork group has established good links with the world's leading researchers in the area, including Dr Mark Humayun in Los Angeles and Prof Rolf Eckmiller in Cologne.
This should help move the research along more quickly, he believes, because everyone involved wants the same thing: a way to restore lost sight.
"There isn't international competition. People are trying to help each other," says Morrissey. "The more people there are looking at this problem, the sooner it will be solved."