Lens coating may keep contacts in eye longer. (Germ Fighter).

An experimental antibacterial coating could enable contact wearers to leave lenses in their eyes for as long as 3 months.

The new coating contains selenium, an element that produces chemical groups called superoxide radicals that kill bacteria, says Ted Reid of Texas Tech University Health Sciences Center in Lubbock, who presented the findings in Boston on Aug. 21 at a meeting of the American Chemical Society. Bacterial growth on contact lenses can limit wearing time and cause infection, which in severe cases leads to blindness.

Reid and his coworkers added common bacteria to silicone lenses, some of which had been coated with a molecule-thick layer of a selenium-containing compound. In these bench-top experiments, bacteria accumulated on the uncoated lenses but not on the coated ones, he reports.

To test the safety of the coated lenses, Reid and his colleagues placed them in rabbits' eyes for 2 months. Each rabbit wore a coated lens in one eye and an uncoated lens in the other eye. There was no sign of eye damage from either lens, Reid reports.

Although toxic in large doses, selenium is beneficial in trace amounts in a person's diet, Reid says. The selenium in one coated lens is about 1 percent the amount in a typical U.S. lunch, he notes. What's more, the coating is chemically bound to the silicone lens, so it shouldn't break free.

Reid is confident enough in his coated lenses that he wore one in his own left eye for a week while wearing an ordinary silicone lens in his right eye. After the week, he removed the lenses and exposed them to bacteria in a laboratory dish. Only the coated lens repelled or killed the bacteria.

Reid next plans to wear selenium-coated lenses for a full month, he says.

"It's cool stuff" comments Jay Kunzler of Bausch & Lomb in Rochester, N.Y., who organized the session at which Reid presented the results. Yet while the selenium compound shows promise, Kunzler cautions that Reid's research still has many hurdles before reaching commercial development. "He has to do a lot more work on it, but it's a good first step" says Kunzler.

Eventually, scientists might coat other bacteria-prone medical devices with the compound, adds Reid, who's already working with companies that make catheters and heart valves. Bacterial infection is an even bigger problem for such medical implants than for contacts, he says.