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Eyeglasses switch focus in a flash

Researchers develop "switchable" lenses, a viable alternative to bifocals associated with grocery stores and old age. Photos: Eye on 'switchable' lenses

A team of researchers at the University of Arizona said Tuesday that they have developed a liquid-crystal eyeglass lens that can automatically change focus depending on the line of sight of the wearer.

Guoqiang Li, assistant research professor of Optical Sciences of the University of Arizona and member of the team of scientists, said the technology could help provide a viable alternative to bifocals, glasses often associated with grocery stores and old age.

switchable lenses

"The lens is 'switchable' between two states. The wearer has a whole picture for viewing," Li said in a telephone interview.

Li and his team published research on their prototype in this week's Proceedings of the National Academy of Sciences journal.

Roughly 90 percent of people older than 45 develop symptoms of presbyopia, an age-related deterioration of the eye that causes an inability to shift focus from distant to near objects, according to research. That's why many people end up wearing bifocals to read the newspaper or restaurant menus. They can see faraway objects, but those nearest are blurry.

Bifocals have a downside, however. A wearer's field of vision is blocked because bifocals are inherently divided and require the user to gaze downward to see nearby. The duality of the glasses can cause headaches.

The lens from the University of Arizona team may solve that problem, according to the researchers. The lens is made up of a 5-micron-thick layer of nematic (polarized rod-like organic molecules) liquid crystal between two layers of glass. The layer of liquid crystal contains a circular array of transparent electrodes.

The electrodes are activated by an electrical field and will cause the liquid crystal to reorient dynamically into rings, focusing light to pass through the lens in a certain way.

The lens' response time to change is less than one second.

Others have tried using nematic liquid crystals for similar corrective lenses, but with little success. Attempts with a thicker or thinner layer of liquid crystal have rendered distortions such as switching to near-sighted focus in critical moments such as when the wearer is driving, according to the research.