New surgical treatments will certainly be important in tackling the growing problem of visual impairment

Spokesperson for charity Fight for Sight

It would then be activated by an electromagnet in a hearing-aid-sized unit fitted behind one ear to generate a magnetic field, activating the eye band's artificial muscle.

The smart eye band could then be altered by clicking the button if you wanted to, say, read a far off notice, then return to reading a book.

The band would allow the eyeball to be squeezed - with the shape changing as 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 people who are long-sighted, this would push the retina backwards, bringing close-up objects back into focus.

Expanding the eye band would mean the eyeball would shorten, bringing the retina forward in short-sighted people to intersect with the focused light, making far-off images sharp and clear again.

Processing images

The artificial muscle is made up of a series of strips of molecular material surrounded by a coil of thin gold wire. Each strip has an electrode at each end.

When the magnetic field is switched on, it creates a pulse of current in the coil, which then builds up a charge on the electrodes.

Positively charged lithium ions in the polymer are attracted to the negative electrode, causing the strips to bunch up and tighten the band around the eyeball.

In the eye, the transparent cornea and the lens focus the image on to the retina, which pre-processes the visual image before sending the information to the brain.

That information is sent to the brain in a large bundle of nerve fibres leaving the back of the eye.

Where someone is short-sighted, the light will focus in front of the retina, so the person will only have blurry images of a far-off object.

Flexible treatment

In people who are long-sighted, the cornea or lens do not focus strongly enough or the eyeball is too short, the light will focus behind the retina, blurring images of close-up objects.

The researchers behind the artificial eye muscle say the necessary surgical techniques are already used to treat detached retinas, and that it would be more flexible than laser surgery which can only correct short-sightedness.

Jim Schwiegerling, of the Optical Sciences Center at the University of Arizona, said the device could help the elderly if they could no longer shift their focus from objects which were far away to ones which were close by.

He said: "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."

A spokesperson for the UK eyesight charity Fight for Sight said: "We welcome research advances into helping improve people's sight as they grow older.

"While this research is at an early stage, new surgical treatments will certainly be important in tackling the growing problem of visual impairment."

Details of the work are reported in New Scientist magazine.