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. Sure, this prototype is rather odd-looking, but its developers say future versions will be indistinguishable from conventional eyeglasses.

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.