Building Longer-Lasting Contact Lenses

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.

More importantly, such low concentrations of selenium should make it safe for use in human eyes. "The amount we put on each lens is one one-hundredth the amount you would have in your lunch," says Reid.

And Reid claims that preliminary laboratory tests seem to bear out its relative safety. As part of his report, Reid noted that selenium-treated lenses were left in rabbits' eyes for up to two months with no apparent ill effects.

Boosted by such research, he says he is currently working with the university to prepare for clinical human trials and seeking FDA certification. If all goes well, Reid says he expects 60-day contact lenses could be available "within two years."

Sit and Wait a Spell

But without human tests, many other eye experts aren't so optimistic — or even convinced that such lenses would be needed.

"It's a kind of interesting premise," says Dr. Lee J. Raykovicv, a doctor of optometry and director of contact lenses at the Wilmer Eye Institute of Johns Hopkins University in Baltimore, Md. "But bacteria isn't the only thing you have to worry about."

  • 1
  • |
  • 2
Join the Discussion
blog comments powered by Disqus
You Might Also Like...