Eyes In Their Stars

NATURE NEWS SERVICE, Aug. 30 -- A relative of the starfish and sea urchin has turned its skeleton into an all-seeing eye.

Near-perfect microscopic lenses in brittlestars' bones are more sophisticated than anything humans can produce, say engineers keen to copy the trick.

Plastic microlenses, inferior to those on the brittlestars, control signals in optical fibers and enhance some displays. They may one day be used in optical computers that process light, rather than electricity.

On the top of the brittlestar's arms, are calcite domes about one-twentieth of a mm across. These focus light, avoiding the blurring that perfectly spherical lenses produce. The intricate calcite crystals are aligned so as not to split light into multiple images. The tiny crystal balls "were too similar to lenses to have been formed by chance", says Joanna Aizenberg of Bell Laboratories and Lucent Technologies, Murray Hill, New Jersey. She happened upon the "incredible structures" while studying the brittlestar Ophiocoma wendtii1.

"It's astonishing that this organic creature can manipulate inorganic matter with such precision - and yet it's got no brain," says Roy Sambles, who works on optics and photonics at the University of Exeter in Britain.

Although brainless, the brittlestar has a nervous system. The lenses focus light onto nerve bundles that run behind them, which presumably pick up the signal, allowing the animal to respond. Together the lenses form a kind of compound eye that covers the animal's upper surface, allowing it to see all around. Aizenberg compares the structure to a digital camera that builds up a picture pixel by pixel.