## Now you see it

> New Scientist vol 160 issue 2159
> - 07 November 1998, page 23

> Retinal implants could soon partially restore sight

> RESEARCHERS in the US predict that within five years they will be able to help some blind people to "see". After successfully transmitting simple electronic images directly to 15 blind people's retinas, they hope to make devices similar to the one used by blind engineer Jordi Laforge in Star Trek: The Next Generation.

> The team, headed by Mark Humayun at Johns Hopkins Hospital in Baltimore, Maryland, report that all 15 patients have been able to see either spots of light or more complex patterns.

> "To see light after so long, it was just wonderful. It was blue," says 71-year-old Harold Churchey, describing his first visual experience after 15 years of blindness. "It was just like switching a light on." Churchey, who lost his sight because of the degenerative eye condition retinitis pigmentosa, is one of the group to whom the team have been able to give some fleeting vision.

> "It was great," Churchey told New Scientist. "They showed me the letter `H'. I had trouble seeing the bottom part at first so I thought it was a `U'. But it was very clear."

> Restoring partial sight using retinal implants

> Humayun previously demonstrated that a person who has lost their sight through diseases of their rods and cones-the cells in the retina that detect light and colour-could be made to see spots of light. This was done by bypassing the rods and cones, and electrically stimulating bunches of the still healthy nerve cells-the ganglia-behind the retina with single electrodes. But he was unsure whether the brain could make sense of more than one artificial signal at a time and worried that the spots would merge into one incoherent blob.

> Last week, however, he told a neuroprosthetics workshop at the National Institutes of Health that he has found that this is not the case. His patients have been tested with a matrix of 25 electrodes on their ganglia, and although this gave poor resolution, it was sufficient for them to recognise simple computer-generated images of numbers, letters or basic shapes. "Some of these patients haven't seen for four decades," says Humayun. "It takes a while for them to see the letters, but once they pick up even a single dot they make quick progress from there."

> Humayun now plans to develop a permanent device with a high enough resolution to restore basic vision. An external video camera (see diagram) contained within a visor will send television images to a chip embedded in the retina. This will translate the video signal into tiny electrical signals on contacts that stimulate the ganglia.

> The team hope to improve resolution so that patients can distinguish, for example, between a window and a door.

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