How safe are soft contact lenses?

• Position: Eyes - Corneal abrasions

Almost one in 13 soft contact lens wearers in a recent study had abrasions on the cornea severe enough to lead to infections or other problems. Mild abrasions--called corneal staining--happen to nearly everyone from time to time, whether or not they wear contact lenses, notes Kelly Nichols, a study coauthor and a clinical assistant professor of optometry at Ohio State University. Columbus. How ever, people who wear contact lenses may be particularly susceptible to developing such abrasions if they don't clean and replace their lenses regularly.

The surface of the cornea regenerates much the same as skin does--old cells slough away in order to make more room for new cells--but in some cases, too many cells wind up being shed. providing a gateway for bacteria, viruses, and other microorganisms to enter the eye. "The abrasions usually heal in less than 24 hours and don't cause problems." Nichols indicates. "We were looking for extreme cases where the subject had a lot of staining." Corneal staining gets its name from the orange-yellow fluorescein dye used to "stain" the surface of the cornea temporarily. After staining the eyes, an optometrist looks at each eye under a special light that causes the dye to fluoresce. The abrasions show up as bright spots on an otherwise smooth, dull surface.

The surface of the cornea--the epithelium--protects the four underlying layers of the cornea. "While any breakdown of the corneal epithelium could provide a possible route for microorganisms to enter the eye, more-severe cases of staining could lead to ulceration or scarring," Nichols points out. Fifty-six percent of the patients had mild staining and eight percent had moderate to severe staining in at least one eye. The severity of staining seemed to depend on how often the subjects replaced their lenses with a new pair, if they wore conventional rather than disposable lenses, and how meticulous they were about cleaning their lenses.

Of the nine...