The past few years have seen several attempts to bring sight to the blind by fitting them with artificial retinas. These implanted devices turn incoming light into electrical signals and pass those signals to nerves that run to the brain’s optical cortex. The result is an image which, though low-resolution and monochrome, is better than no image at all.

Which is fine for those whose blindness is caused by a problem in their eyes, such as macular degeneration or retinitis pigmentosa. But some blind people, especially some blind from birth, are unable to see not because their eyes do not work but because their optical cortexes are damaged. For these people, an artificial retina is useless.

Zeev Zalevsky, a researcher at Bar Ilan University in Israel, hopes to change that. Dr Zalevsky, observing the brain’s plasticity, wonders if it might be possible to recruit a different part of the cortex to stand in for the damaged tissue. He and his colleagues are now trying to build a contact lens which does just that.

Unlike an artificial retina, which has to be implanted, a contact lens sits on the cornea—the convex window through which light passes into the eye. The cornea has no nervous connection with the visual cortex. It is though, as any wearer of contact lenses will know, exquisitely sensitive. And it is this sensitivity that Dr Zalevsky plans to exploit.

His lenses will contain a grid of 10,000 tiny electrodes, each of which will stimulate—and thus irritate—a small area of the cornea beneath. The electrodes themselves will be responding to signals transmitted wirelessly from two tiny cameras mounted on what is, in effect, a pair of spectacles.

The hope is that the wearer can learn to interpret the pattern of stimulation as an image. Whether that is possible remains to be seen. But there are reasons for hope.

First, it is well known that although different areas of the brain perform different roles, the boundaries between these functions can be quite plastic. The visual cortex of blind people may, for example, be used for language processing instead.

Second, many blind people learn to do by touch something that the sighted do by vision—namely reading. Louis Braille’s system of raised-dot calligraphy can be read as rapidly by running the fingertips over it as a page of more conventional print can be read by scanning it by eye.

Third, Dr Zalevsky has conducted some encouraging preliminary experiments. He does not yet have permission for clinical trials on people’s eyes but, inspired by Braille’s system, he has been feeding electronic images to volunteers’ fingertips instead. After a suitable period of training such volunteers are able to recognise simple shapes, such as letters of the alphabet.

This is not proof Dr Zalevsky’s contact lenses will work. His volunteers were sighted, and therefore knew what images are. Someone blind from birth would not. And learning to recognise a finite set of characters is different from dealing with the indeterminate complexity of the real world. If the technology does work, though, it will bring at least a simulacrum of vision to many who now have none—and will do so without the need for surgery.

Source: The Economist