Using bifocals can be a chore, as they are usually designed for close reading and don't work well when trying to see with the whole field of vision.

But the people at Roanoke, Va.-based PixelOptic have an answer -- an electronic bifocal that can be preset to change the refraction of a lens.

The idea is actually an old one. In a liquid crystal display the pixels are made black or clear when an electric charge is passed across them. This changes the orientation of the molecules between two layers of glass or plastic, making them opaque.

The electronic bifocals do the same thing, except that instead of changing the opacity of the material, the electric charge alters its index of refraction. By sweeping a finger along the rim, one can turn the electric current on or off. Compared to many of the gadgets at this year's Consumer Electronics Show, this one is subdued and decidedly un-flashy, but it has a very pracical use.

When I wore bifocals I kept having to raise my head or lower it if I wanted to see some things, said Stephen Holt, chief financial officer. And for many people who need reading glasses the glasses are only good for close reading. The reason is that as people age, their eyes lose some flexibility and have a harder time changing focus.

The glasses can be charged up and the batteries last for several hours, Holt says. With an aging population this kind of device will become more necessary. There are lots of people in their 40s, he noted, which is the age that most start needing reading glasses.

Another plus is that the glasses themselves don't cost much more than conventional lenses - the premium should be about 20-30% -- and with the ability to alter the lenses you only need one pair, so it would be a net savings.

The first glasses should start going on sale in April, Holt says. The company has received a round of venture funding from the Carlyle Group, Delphi Ventures and Panasonic's venture capital arm.