American authorities are warning that cosmetic contact lenses, ones inscribed with fanciful designs or words, could cause blindness.

The Food and Drug Administration (FDA) says the lenses, which are sold without prescription, are illegal.

The agency has stopped imports of the lenses starting on Monday. Officials also said they would seize unapproved lenses sold in convenience stores and other markets.

Decorative lenses with swirls, words or coloured designs have recently hit the market.

The FDA cites reports of corneal ulcers — abrasions that can lead to infections — and other eye injuries linked to the products. In some cases, corneal transplants were required.

The administration says consumers should not wear any contact lenses unless they are properly prescribed and fitted by an eye-care professional.

With the coming of Hallowe'en the lenses are popping up in stores and in ads. One ad in the Toronto weekly NOW for "Crazy Lenses" features a teenageer with yellow ringed lenses. The ad says: "Explore the world of outrageous fashion eyeware."

"People get the idea since they're out there that they don't pose the same safety issues," says Lester Crawford of the FDA. "But these things are risky."

The only cosmetic lenses approved for sale are colored prescription-only lenses. These lenses are made under sterile conditions and consumers are required to be told how to insert and care for them.

There's no word yet from Health Canada whether they will do the same.