Photonics Spectra: By applying voltage to liquid crystals, eyeglass lens focusing power can be changed, having the potential to replace bifocals, trifocals, multifocals and other applications that require multiple levels of focusing power.
One of the difficulties in using bifocals is that the wearer must look up and down through the lenses depending on the desired focusing power. Progressive lenses that have focusing power that progressively becomes stronger as you look toward the bottom part of the lenses have eased the difficulty but the main problem remains: the wearer must look up and down.
Guoqiang Li, an assistant research professor of optical sciences at the University of Arizona in Tucson along with Nasser Peyghambarian and a team from Arizona and the Georgia Institute of Technology in Atlanta have demonstrated a liquid crystal-based lens with the capability of quickly switching focusing power by applying an electric signal.
A 5 micron-thick layer of E7 liquid crystal is used between two flat pieces of glass. The liquid crystals are controlled by applying 2 volts or less that changes the effective reflective index resulting in the change of focusing power.
First of all, this sounds like a technological advancement, which it is, but when applied to wearers of multifocal lenses, the applications might be quite limited. The cost of such a devices would be too expensive for most. Second, most wearers of glasses prefer something light, but this device would be quite heavy. Third, for those that require quick switching of near vision to far vision and back, the use of a switch to turn the device on or off makes it impractical.