Building Longer-Lasting Contact Lenses

Aug. 23 -- For millions of people with poor eyesight, contact lenses are an attractive alternative to cumbersome eyeglasses. But they can also be somewhat of a hassle, too.

The No. 1 complaint: Removing and cleaning the lenses on a regular basis.

New advances in lens materials are making routine cleaning less of a necessity.

Last year, for example, the Food and Drug Administration approved the sale of contact lenses that can be worn continuously for up to a month. Made of so-called "bio-compatible" material, these new "extended wear" lenses allow more oxygen to pass through to the surface of the eye while resisting the build-up of harmful bacteria and protein.

While such lenses have just begun to hit their stride with consumers, Tim Reid, a professor of ophthalmology and cell biology at Texas Tech University Health Science Center in Lubbock, Texas., says he's ready to take contact lenses to a level that would make even the laziest wearer rejoice.

Selenium Sauce

At an American Chemical Society meeting in Boston this week, Reid claims to have developed a way to make contact lenses that may be safe enough to wear for months at a time.

The secret, he says, is to coat the lenses with a tiny amount of selenium — a naturally occurring mineral that can be found in many foods.

The selenium works with the chemicals in the tears of the eyes to produce super-oxide radicals. These chemical agents kill bacteria spores through oxidation and prevent the bacteria from attaching to the lens.

"Selenium is a neat material," says Reid, who notes that about 150 micrograms are needed in human diets to maintain a healthy immune system. But increase the amount to a mere 3 milligrams and it's enough to make a person sick.

"It's an age-old killing mechanism," he says. "White blood cells generate super-oxides as a kill mechanism and bacteria can't develop a resistance to it."

Simple But Is it Safe for Humans?

Such lethality means that it doesn't take much to stop bacteria dead in its tracks on a lens. Reid says that a quick soak in a special selenium solution would leave a layer just one-molecule thick. Such minute quantities wouldn't affect a contact lens' optical properties or block the flow of oxygen to a wearer's eye.