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Better bifocals on the horizon

April 3, 2006 By Jacqueline Ruttimann This article courtesy of Nature News.

Electrical lenses switch modes at the flick of a switch.

Wearers of unwieldy bifocal spectacles, take heart. A new kind of lens could offer a neat solution to the problem of switching between two lens types. The electrically powered design can shift from one lens power to another in the blink of an eye, or in this case, the flip of a switch.

This is good news for bifocal and trifocal users, which will include most of us at some point in our lives. Some 90% of people over the age of 45 develop presbyopia, in which the lens loses its flexibility and becomes less able to switch its focus from distant to near objects.

The most common solutions to this affliction are bifocal or trifocal lenses, which are divided into two or three different areas, respectively, each with its own focusing power. However, such glasses limit the field of view and require the user to use a specific area of the lens to see a certain object. Close objects, for example, must be viewed by peering downwards, which can lead to dizziness and headaches. Even varifocal lenses, which feature a gradation in power, require users to raise or lower their gaze to see near or far.

We want to improve the quality of life for a large population.
Guoqiang Li
University of Arizona
Researchers therefore set out to create a lens that can offer different focusing powers throughout its entire area. "We want to improve the quality of life for a large population," says Guoqiang Li of the University of Arizona in Tucson. He and his colleague Nasser Peyghambarian led a team that has created a liquid-crystal lens that can adaptively change its focusing power when an electric current is applied by tiny concentric electrodes embedded in the structure.

Crossing the line

Liquid crystals are half liquid and half solid. They have a variety of uses, both in technology and in the natural world, such as in spider silk. What makes them so applicable for optics is that these molecules are usually orientated in a certain direction. But by applying an electrical voltage, the crystals can be reshuffled to adopt a different, yet still uniform, configuration. And changing the configuration, which requires no more voltage than that of an ordinary commercial battery and takes less than a second, can offer different focusing powers.

With no electric current, Li's lens lets users view distant objects. But switch on the current, and the lens becomes more magnifying, allowing close-up objects to be viewed. The researchers designed the lens this way around so that activities that required distance vision, such as driving, are done with the power switched off. This minimizes the danger should the power fail.

Seeing clearly

When used in the clinic, Li reported that the volunteers were amazed at the results. "When they put them on, they said 'Wow, I can see the books very clearly'," he says. The results are reported in Proceedings of the National Academy of Sciences USA1.

The patients are not the only ones with a vision. The eyewear division of Johnson & Johnson that collaborated with Li would like to commercialize these practical peepers. Li says that the technology could be on the market in as little as two or three years. And Li ultimately wants to develop the technology so that the lens can automatically choose the focusing power, "just like a camera lens".

It's a promising idea, says Shuliang Jiao, an ophthalmologist at the University of Miami, Florida. Given the proportion of older people who currently wear bifocals, the technology could potentially make life better for millions of people, he says.

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  1. Li G., et al. Proc. Natl Acad. Sci. USA, doi:10.1073/pnas.0600850103 (2006).


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