Glasses that change from “long distance” to “reading” mode at the flick of a switch could prove a revelation for many wearers.
Researchers have developed a prototype that uses liquid crystals to change focus in an instant, thus preventing the eye strain induced by wearing conventional bifocal glasses. Focusing through specific portions of a bifocal lens causes many users to become dizzy or disoriented, while others report increased eye fatigue.
“Bifocals effectively work the same way they have since they were invented by Benjamin Franklin,” says Nasser Peyghambarian, a professor of optical sciences at Arizona State University, US, who helped develop the “dynamic” glasses. “But as any of more than 40 million people in America who need bifocals know, they’re a pain.”
Fresnel lens
The dynamic glasses change focus using a 5-micron-thick layer of nematic liquid crystal, sandwiched between two pieces of glass. Molecules of the liquid crystal reorient themselves when exposed to an electric field and the researchers used this to create a type of dynamic Fresnel lens.
In a normal Fresnel lens, concentric rings are carved into a piece of glass causing light to become focused in a similar way to a conventional lens. Dynamic glasses mimic the Fresnel effect using concentric circles of clear electrodes on the pieces of glass containing the crystal. Activating these electrodes causes the liquid crystal to align into rings and focus light passing through the lens.
A company called PixelOptics, based in Virginia, US, plans to sell glasses containing dynamic lenses commercially within two years. “The prototype is pretty bulky, but when these hit the streets they’ll be virtually indistinguishable from other, very stylish glasses,” says Ronald Blum, CEO of PixelOptics.
Infrared laser
PixelOptics first developed the idea of dynamic focusing while working on large lenses for computer screens. Ideally, these would have allowed near-sighted and far-sighted people to read their monitors without their spectacles. “As screens got thinner and thinner, though, the idea became less practical,” Blum says. “So instead we decided to move the technology from the computer to the computer user.”
The first commercial dynamic glasses will only be able to switch between a person’s normal vision and their “reading” prescription. However, by applying different voltages and by changing the number of current-carrying rings within each lens it should be possible to produce different magnifications using the same lens, researchers say.
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