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updated 8/27/2010 3:59:08 PM ET 2010-08-27T19:59:08

Deteriorating eyesight is nothing new for the over-40 crowd, but the fix for astronauts isn't so simple.

Wearing bifocals or progressive lenses is limiting because the viewing areas for reading are small and fixed at the bottom portion of the lenses. Astronauts living in the gravity-free world of space often need to read material above their heads or in other parts of their visual fields.

Single-vision lenses would take care of that problem, but switching pairs of glasses for different tasks presents logistical challenges, especially in microgravity where objects tend to float away unless they are secured.

A California company thinks it has the solution -- adjustable glasses that reshape themselves with the flick of a finger.

"You always had the feedback circuit built into your brain for focusing. You just have to redirect that impulse to your finger," inventor Stephen Kurtin, with Zoom Focus Eyeware, told Discovery News.

The glasses, which weigh about the same as conventional glasses, contain two pairs of lenses. The rigid outer lenses are manufactured to meet an individual's prescription for distance vision -- or left clear if none is needed. The flexible inner lenses have a transparent expandable pouch that holds a small amount of liquid silicon oil.

Adjusting a slider bar on the bridge of the frame pushes the fluid around the pouch, changing the shape of the lenses.

The technology replicates the way the human eye works -- or used to work up until about age 45 or so. Over time, people lose the ability to focus on objects close up, though scientists aren't exactly sure why. The condition, known as presbyopia, unfolds gradually until one day reading becomes a challenge.

"It feels like you fell off a cliff, but it's just this slow change that fell past this critical number," Kurtin said.

Kurtin's glasses, known as TruFocals, have round lenses, which he says is the optimal shape for focusing vision.

"They're not the most stylish -- very Harry Potter-looking," said NASA optometrist Robert Gibson at the Johnson Space Center in Houston, who has turned over the glasses for flight certification tests after initial positive feedback from astronauts and other patients.

"The astronauts don't really care what they look as long as they can see," Gibson said. "These give you crystal-clear optics without any distortion whatsoever. That becomes more critical in an enclosed environment like the shuttle or the space station or the Russian) Soyuz."

"I think it's a nice solution," said Gibson, who told Discovery News he has no financial relationship with the manufacturer. "These are going to be a nice option if they get certified for flight."

TruFocals, however, wouldn't work during spacewalks, Gibson added.

"Obviously, you can't reach up there and make an adjustment."

Kurtin said he already tried developing auto-focus lenses, but without success since it is the brain that determines what the eye is viewing, not the tilt of the head, the angle of the eye or even the opening of the lens.

Making the lens adjustment manually is not as big of a deal as it sounds, Kurtin added.

"After a day or two, it becomes totally automatic. It's just like scratching your ear," he said.

© 2012 Discovery Channel

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