Variable focus at the flick of a switch
05 April 2006
Aging eyes could soon have an alternative to bifocal spectacles, with the development of liquid crystal lenses that focus on near or distant objects at the flick of a switch.
Guoqiang Li and colleagues at the college of optical sciences, Tucson, Arizona, US, made use of a property of certain liquid crystals (LCs), to create prototype spectacles with lenses made from so-called nematic LCs. The structure of these LCs can easily be aligned by magnetic or electric fields.
Li's prototype spectacles were made with nematic LC lenses, patterned by photolithography with circular arrangements of transparent electrodes. The lenses can change their refractive index, and so their focusing power, with changes in applied voltage. 'Our current lens has two states, on and off,' Li told Chemistry World. 'In the on state, the lens has certain focusing power and performs near vision correction, while in the off state, the lens has no optical power and corresponds to distance vision.'
The age-related eye condition presbyopia makes it harder for the eye to shift focus from distant to near objects. Bifocal lenses are used to correct the condition, but limit the range of vision, with spectacle wearers having to lower their eyes for close work like reading, which can cause dizziness. With the LC spectacles Li hopes to stop the need for peering through the bottom half of the lens.
The lenses have what is known as power-failure-safe configuration, which means no power is needed for distance vision tasks like driving, Li explained.
The prototype spectacles are not about to win any fashion awards, but Li says they will be making them 'more compact and stylish'. Li is in talks to commercialise the specs and hopes to see a product in two or three years.
G Li et al, Proc. Natl. Acad. Sci. USA, 2006, (DOI: 10.1073/pnas.0600850103)