A long-cherished science fiction dream is approaching reality, as researchers in the US get closer to an eye implant that restores sight to the blind. Aimed at those suffering from macular degeneration and retinitis pigmentosa, where the light-sensitive cells on the retina stop working but the nerves survive, the project is a $9m collaboration between US national research labs and universities.

"The aim is to bring a blind person to the point where he or she can read, move around objects in the house, and do basic household chores," said Sandia Labs project leader Kurt Wessendorf in a statement. "They won't be able to drive cars, at least in the near future, because instead of millions of pixels, they'll see approximately a thousand. The images will come a little slowly and appear yellow. But people who are blind will see."

The system, also known as a Multiple-unit Artificial Retinal Chipset (MARC), involves multiple components mounted both inside and outside the eye. A spectacle-mounted camera takes video that is then processed and transmitted into the eye by radio. There, a chip made from micro-machined silicon and protective coatings receives the signal and extracts data with which to stimulate the retinal nerves. Like a crystal radio set, it also extracts the power it needs to run from the radio signal, removing the need for any external wires or internal power pack.

The mammalian eye has an evolutionary flaw, whereby the cones and rods lie behind the layer of neurons that feed the optic nerve. This reduces visual acuity and gives us our blind spot, but is actually helpful when it comes to wiring up retinal implants. The MARC receiver sits on top of the retina, making direct contact with the nerves through a 10x10 array of electrodes. By designing the MARC receiver to have the same buoyancy as the aqueous humour in the eye, and by doing as much processing outside as possible, the stress on the retina and any heat dissipation problems are kept to a minimum.

The whole device is the result of research at John Hopkins and North Carolina State universities, the University of Southern California and Oak Ridge National Laboratories. Other labs, such as Sandia, Los Alamos and Laurence Livermore, are modelling neural pathways and testing new materials.

Many problems and questions remain, such as the best waveform for stimulating the nerves, the best way to package the chip to keep it and the eye healthy, the best way to connect the chip to the retina, and how to transmit colour images. The project is due to finish in 2004, by which time the team hope the picture will be up to 33x33 pixels, enough to distinguish text and faces, and will be available as a treatment for blindness.

One of the project instigators, Mark Humayun from the University of Southern California, said: "There is a considerable amount of advanced technology literally on the shelf or already being used for defence purposes that we could use to help solve blindness and greatly propel forward the entire field of medicine."

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