Eye ball.

Last February, soccer fan Stephanie Berndt donned decorative contact lenses to support her favorite team.

"Theatrical contact lenses are hot items, particularly with teens," says Dr. Thomas Steinemann, an ophthalmologist, or eye doctor, at MetroHealth Medical Center in Cleveland, Ohio. But those wishing to sport the lenses will have to consult an eye doctor first. That's because, as with any contact lenses, wearers need a proper fitting to avoid serious infections.

Like vision-correcting lenses, the designer discs cover each eye's cornea, or the clear membrane that covers the colored iris and the pupil (the center of the eye where light enters). Each person has a slightly different eye shape and size. "Normally, lenses are fitted [by licensed professionals] to the curvature of the eye," Steinemann says.

The same goes for the trendy contacts. A perfect fit means the lens is snug--but not too snug. That way, watery tears can seep beneath the plastic lens, washing away foreign substances such as dust and bacteria. If the lens is too tight, tears can't wash over the cornea. As a result, the cornea becomes a breeding ground for bacteria that can cause serious eye infections, he says.

Another eye-opener: "If the lenses fit too tightly, they can cause abrasions on the cornea, which open the door to [harmful] bacteria," explains Steinemann.

Until last November, wearers could buy the patterned lenses from drug stores and supermarkets. That changed when a federal law passed to safeguard lens wearers. The law states that cosmetic contacts are "medical devices" and must be regulated by the Food and Drug Administration.

Now, people who want a visual makeover will have to get their lenses from a doctor's office. So experts can give wearers an eye-friendly fit. Plus, eye doctors will give instructions for the proper care and cleaning of the lenses to keep them bacteria-free.

When it comes to contact lenses, Steinemann warns: "One size doesn't fit all."