Eyes like a hawk


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<!--intro-->Think you've got perfect vision? Think again. Pablo Artal reckons he can double the sharpness of anybody's vision, no matter how good it is to start with. He revealed his "smart spectacles" technology at a conference on adaptive optics in Murcia, Spain, last week.<!--/intro-->

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Few people would choose to wear Artal's prototype, as the computer hardware it relies on takes up a full square metre of desk space. "But the key optical component is very small and cheap," says Artal, a researcher in the optics laboratory at the University of Murcia.

Conventional spectacles correct for poor focusing and astigmatism in the eye's lens. But almost everyone has subtle additional faults which vary as their pupils dilate and their eyes focus. To try and correct for these problems, Artal and his colleagues turned to the techniques of adaptive optics, which are more commonly used in telescopes and spy satellites.

In adaptive optics, light from a star, say, is bounced off a mirror which changes shape to compensate for the distortions introduced by fluctuations in the atmosphere. It is these fluctuations in the density of the atmosphere that make stars twinkle. Artal's spectacles do the same thing for transient imperfections in the eye, correcting for them 25 times every second. "Everything sharpens up as you switch on," he says.

<img src="http://www.newscientist.com/ns_images/2266/226629F2.JPG" align=right hspace=7>In his prototype spectacles, a low-intensity infrared laser beam bounces off the back of the retina and into a sensor via a deformable mirrored membrane. The membrane's shape is controlled by an electric field created by a microchip underneath it.

A computer works out how much the infrared beam has been distorted by the eye's lens and tells the mirror chip to deform the mirror in real time (see Diagram). Because light reaches the user's eyes via the deformable mirror, the computer can ensure that the user sees a perfect image.

The mirror's shape is updated 25 times per second--about 5 times faster than aberrations vary in the eye, so the wearer is unaware of the moving mirror.

Artal says that someone wearing the new specs can see at a range of 12 metres objects so small that someone with 20:20 vision can't see them farther away than 6 metres. But Fred Fitzke, an ophthalmologist at University College London, is more cautious: "At the moment, we don't know what other limits there are to vision--like the structure of photoreceptors in the eye, or whether the brain can even use the extra information. But I look forward to finding out with this kind of device."

As well as having possible military applications, the super specs can be used in reverse to take real-time precision images of the retina. "You can use it to take microscopic images of individual cells and diagnose eye diseases very early," says Austin Roorda of the University of Houston.

Eugenie Samuel

From New Scientist magazine, 25 November 2000.