Contacts for aging baby boomers' eyes?

Some people say your eyesight is the first to go. You have to hold books and newspapers at arm's length to read them. When your arms get too short for that to work, there's no denying it: You've got presbyopia, more commonly known as far-sightedness. Contact lens makers recognize this fact of life and see a huge potential market in the aging baby boomer population. For most far-sighted people, however, lenses made according to current technology would be impractically thick.

Now, researchers in France are developing a way to address this limitation.

Instead of shaping the lens to aid eyesight, Isabelle Calderara, a chemist at the contact lens maker Essilor in Creteil, and her colleagues have made a lens that focuses light with a graded refractive index. In other words, the lens' power to bend light rays changes from the center to the edge, a technique that can potentially be used to make more practical corrective lenses for far-sightedness.

The French researchers shine light on the building blocks of a polymer, causing them to link together. The more light, the greater the number of links and the denser the polymer. Density determines the polymer's refractive power, so shining different amounts of light on adjacent parts of the lens creates a gradation.

But one polymer isn't enough, Calderara says. To get the degree of light-bending needed, it's necessary to intertwine two different polymers in the same lens. After the first polymer is linked appropriately, Calderara and her colleagues add the building blocks of a second polymer, shine light on it, and create another network that penetrates the first. The second polymerization doesn't affect the first linked structure, but it must be carefully controlled or the lens will lose its flexibility.

"It's very exciting," says polymer scientist L.H. Sperling of Lehigh University in Bethlehem, Pa., who studies interpenetrating networks. "I'm always interested in new materials and new applications, and this is very different," he adds. Russian scientists did the same thing with solid polymers, he notes, but no one has done it in soft, hydrophilic polymers-materials used for contact lenses.

It's too early to say whether this technique will be used commercially, Calderara says. The next challenge, she says, is to see what range of lens powers they can make.