Presbyopia is a common visual condition, in which the eye's lens stiffens to the point that it can't focus on close objects. Glasses, surgery and regular contact lenses do help, but they also cause a loss in contrast, sensitivity and night vision. That's why scientists from the University of Wisconsin, Madison are developing an alternative – self-focusing contacts that are inspired by a fish.

The fish in question is the elephant nose fish, which has evolved a special retinal structure in order to see in dim, muddy water. Its retinas are made up of a series of deep cup-like structures with reflective sidewalls, which help to gather light.

Led by Dr. Hongrui Jiang, the U Wisconsin researchers have replicated this structure using man-made materials. In their case, thousands of microscopic "cups" are lined with reflective aluminum, and each one is housed within a tiny finger-like glass protrusion. As light hits these protrusions, it is focused by the reflective sidewalls. Already, the scientists have successfully used the system to enhance images captured by a mechanical eye model in the lab.

The structure would be embedded in the front of a flexible, transparent contact lens. With the application of an electrical current, that lens could be made to change shape and focal length as the eye changes focus, bringing close-up images captured by the structure into sharp view. Power would come from a built-in solar cell, and would be stored in a network of nanostructures within the lens.

It sounds promising, although Jiang states that a working prototype contact lens is probably still five to 10 years away. Once it is developed, however, he believes that it shouldn't be much more expensive than a regular lens.

His team is also working on presbyopia-correcting contact lenses that are based on insects' compound eyes.

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