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A new generation of contact lenses that project images in front of the eyes is a step closer after successful animal trials, say scientists.

The technology could allow wearers to read floating texts and emails or augment their sight with computer-generated images, Terminator-syle.

Early tests show the device is safe and feasible, says the University of Washington in Seattle.

But there are still wrinkles to iron out, like finding a good power source.

Currently, their crude prototype device can only work if it is within centimetres of the wireless battery.

And its microcircuitry is only enough for one light-emitting diode, reports the Journal of Micromechanics and Microengineering.

But now that initial safety tests in rabbits have gone well, with no obvious adverse effects, the researchers have renewed faith about the device's possibilities.

They envisage hundreds more pixels could be embedded in the flexible lens to produce complex holographic images.

For example, drivers could wear them to see journey directions or their vehicle's speed projected onto the windscreen.

Similarly, the lenses could take the virtual world of video gaming to a new level.

They could also provide up-to-date medical information like blood sugar levels by linking to biosensors in the wearer's body.

Delicate materials

Lead researcher Professor Babak Parviz said: "Our next goal is to incorporate some predetermined text in the contact lens."

He said his team had already overcome a major hurdle to this, which is getting the human eye to focus on an image generated on its surface.

Normally, we can only see objects clearly if they are held several centimetres away from the eye.

The scientists, working with colleagues at Aalto University in Finland, have now adapted the lenses to shorten the focal distance.

Building the end product was a challenge because materials used to make conventional contact lenses are delicate.

Manufacturing electrical circuits, however, involves inorganic materials, scorching temperatures and toxic chemicals. Researchers built the circuits from layers of metal only a few nanometres thick, about one thousandth the width of a human hair, and constructed light-emitting diodes measuring one third of a millimetre across.

Dr Parviz and his team are not the only scientists working on this type of technology.

A Swiss company called Sensimed has already brought to market a smart contact lens that uses inbuilt computer technology to monitor pressure inside the eye to keep tabs on the eye condition glaucoma.