Mohsen Shahinpoor and his team at the University of New Mexico call their artificial muscle a "smart eye band". It will be stitched to the sclera, the tough white outer part of the eyeball, and activated by an electromagnet in a hearing-aid-sized unit fitted behind one ear.
Most of the eye's focusing is done by the cornea, the hard transparent surface that covers both the pupil and the iris; the lens is responsible only for fine-tuning. Light travels through the cornea and lens to focus on the retina at the back of the eyeball.
The closer an object is, the farther back in the eye it will be focused. The lens compensates by adjusting its strength to bring the focus back onto the retina.
If the cornea or lens don't focus strongly enough or the eyeball is too short, the light will focus behind the retina, blurring images of close-up objects. This is long-sightedness. Conversely, if the eyeball is too long, the light will focus in front of the retina, yielding the blurry images of far-off objects characteristic of short-sightedness.
Tightening the smart eye band causes the eyeball to elongate, just as squeezing the middle of a peeled hard-boiled egg causes the egg to lengthen. In long-sighted people this pushes the retina backwards, bringing close-up objects back into focus. Expanding the eye band causes the eyeball to shorten. In short-sighted people this will bring the retina forward to intersect with the focused light, making far-off images sharp and clear again.
Stitching a band of artificial muscle to your eyeball sounds drastic, but Shahinpoor says the necessary surgical techniques are already commonly used for treating detached retinas. He claims his smart eye band is far more flexible than laser surgery, in which a laser flattens the cornea by eroding part of it. Laser surgery can only correct short-sightedness.
With the smart eye band implanted, you'd set your eyes to read a book, say, by clicking a button on the device sitting behind your ear. This would generate a magnetic field to activate the eye band's artificial muscle.
The artificial muscle comprises a series of "bi-strips" (see Graphic), each made up of two lengths of a biocompatible polymer containing lithium ions, surrounded by a coil of thin gold wire. At the end of each bi-strip is an electrode. Switching on the magnetic field induces a pulse of current in the coil, which in turn builds up a small charge on the electrodes. The positively charged lithium ions in the polymer are attracted to the negative electrode, causing the whole bi-strip to bunch up and tighten the band around the eyeball. So the eye's focal length becomes electronically controllable.
Though Shahinpoor's idea is still on the drawing board, Jim Schwiegerling of the Optical Sciences Center at the University of Arizona says the technology could be of enormous benefit to older people who have lost the ability to change focus from distant to near objects. "When you sit down to read a book, you could just switch it on, and when you are done reading, you could turn it off and go out and drive a car," he says. Shahinpoor will present the design for his bionic eye at an optical technology con-ference in San Diego, California later this month.
Author: Catherine Zandonella and Paul Marks
New Scientist issue: 23rd March 2002
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