Researchers have developed an electro-optic lens that can shift its focusing power with the flick of a switch, and may someday replace bifocal lenses.

Dr. Nasser Peyghambarian of the University of Arizona at Tucson and colleagues report the results of tests of prototype spectacles in the online Early Edition of the Proceedings of the National Academy of Sciences.

The lenses consist of a liquid crystal sandwiched between two pieces of glass, similar to familiar LCDs like those found on digital clocks. In this case, instead of showing numbers, the crystal contains a circular array of transparent electrodes, which turn the glass into a lens when a 2-volt charge is applied.

When the voltage is turned off, the lens is plain with no focusing power and does not interfere with distance vision.

In their article, the researchers report on a 1-diopter version of the lens, but Peyghambarian told Reuters Health he and his colleagues have made a number of lenses of different strengths.

The next step, he said, will be to develop a mechanism that will allow the lenses to focus automatically, similar to a camera’s range-finding mechanism.

SOURCE: PNAS Early Edition, online April 3, 2006.