Presbyopia is a visual defect which affects many people over 40 years old, including myself. As we cannot focus on close objects, we tend to rely on bifocal glasses. But with bifocals, the two parts of the lenses focus separately on two different distances and it can be difficult for some people to feel comfortable. Now, based on research done at the University of Arizona, a company named PixelOptics plans to sell electrically adjusted eyeglasses. With these eyeglasses, the entire lens will switch to the desired focus.
Before going further, let's look at a simulation of what you could see with these glasses when you're not too far from what you're watching (Credit: PixelOptics). On the left is what you could see with conventional progressive glasses while the right image shows what you could see with a PixelOptics pixilated lens.
Here is how these switchable glasses are working according to one of the inventors, David Mathine of the University of Arizona?
To make eyeglass lenses that change focus electrically, the researchers created sandwiches of glass sheets separated by a fluid layer 5 micrometers thick. The filling consists of a transparent substance, a type of liquid crystal, that's made up of rod-shaped molecules suspended in a liquid. The team used precise computer-chip-manufacturing methods to apply a bull's-eye pattern of transparent electrodes to the inner surface of one of the glass sheets.
In response to voltages applied to those electrodes, the liquid-crystal rods rotate into new orientations, explains Guoqiang Li of the University of Arizona and a member of the development team. The rod orientation determines the speed at which light passes through the liquid-crystal layer. Light rays bend as they traverse the layer and so can become focused, much as they would when passing through an ordinary lens.
Below is another simulation for far vision comparing conventional progressive glasses (left) and PixelOptics pixilated lens (right) (Credit: PixelOptics).
This research work has been published by the Proceedings of the National Academy of Sciences under the name "Switchable electro-optic diffractive lens with high efficiency for ophthalmic applications" (Vol. 103, Number 16, Pages 6100-6104, April 18, 2006). Here is a link to the abstract of this paper which offers some additional details.
The operation of these spectacle lenses is based on electrical control of the refractive index of a 5-ìm-thick layer of nematic liquid crystal using a circular array of photolithographically defined transparent electrodes. It operates with high transmission, low voltage, fast response (<1 sec), diffraction efficiency (> 90%), small aberrations, and a power-failure-safe configuration. These results represent significant advance in state-of-the-art liquid-crystal diffractive lenses for vision care and other applications. They have the potential of revolutionizing the field of presbyopia correction when combined with automatic adjustable focusing power.
Finally, it's interesting to note that the military are interested in these new glasses, but not exactly for the same reasons. In "Pixeloptics To Develop SuperVision For US Military," Space War wrote that "PixelOptics has announced that it will receive $3.5 million from the Defense Department to develop SuperVision, a technology that enables our military men and women to have better than 20/20 vision."
Even if I don't want such a SuperVision, I would be delighted to replace my current bifocals with always-on focused glasses. Don't you agree?
Sources: Peter Weiss, Science News, Vol. 169, No. 16, April 22, 2006; and various web sites
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