Hope Over Self-Focusing Glasses

US researchers have designed glasses which can change focusing power by harnessing the images seen by the eyes. The University of Arizona team has created lenses which use electrodes to alter the optical properties of liquid crystal between layers of glass. The team believes they could one day replace bifocal and varifocal glasses, Proceedings of the National Academy of Sciences journal reports. But UK experts suggest the lenses would be heavy and require thick frames.

As the human eye ages, its outer layer can lose its flexibility, often resulting in an inability to shift focus from distant to near objects. The field of view is limited in such bifocal eyeglasses, requiring the user to gaze down to accomplish near visions tasks and in some cases causing dizziness and discomfort. Area-divided bifocal lenses are a common remedy but users still need to move their gaze between the upper and lower lenses as they switch between far and near vision tasks. Varifocal glasses which graduate more slowly are becoming common but still require shifts in gaze.

The model designed by the US team uses thick lenses to help support the weight of the liquid crystal. It relies on a series of concentric rings of tiny, transparent electrodes that control the optical properties of a thin layer of liquid crystal trapped between two layers of glass. Liquid crystal is used because the semi-solid fluid can be made to change properties to improve optical imaging. The device operates at low voltage and can switch focal power in less than one second after registering the vision seen through a lens placed on a person's eyes. If electrical power is suddenly lost, the lens reverts to a configuration with no focusing power, which makes it safe for use while driving, the researchers said.

However, UK experts remain unconvinced the glasses offer a viable alternative to bifocal and varifocal lenses. Cardiff University optometry expert Professor Mike Boulton said: "The problem is that liquid crystal is quite heavy and expensive. "Because it is heavy it means thick frames have to be used and people often choose glasses partly because of the style so I cannot see these glasses replacing bifocal and varifocal."

Source: BBC News

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