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Dr. Paul Kline, an optometrist in Fort Lauderdale, Fla., said every year around Halloween a grey market in decorative contact lenses pops us.

"Normally they're distributed through the standard licensed channels, but there's always some leakage," said Klein, who chairs the American Optometric Association's contact lens and cornea section.

"Unfortunately consumers that purchase these lenses through non-professional channels don't get the kind of instruction and wear information necessary to be able to handle the lenses properly, care for the lens properly, nor are they made aware of the side effects and what to look for," he added.

The lack of information puts consumers at risk of eye irritation, inflammation, infection and even, rarely, loss of sight, according to Klein.

Infection is a particular concern, he added, given recent recalls of contaminated contact lens solutions linked to hundreds of cases of potentially blinding infections.

Contact lenses, whether corrective or decorative, are regulated as medical devices by the Food and Drug Administration. They must be sold through a licensed medical practitioner who can fit them and provide instruction on use and care.

"I don't want to give anyone the impression that this is an epidemic, but clearly one lost eye is one too many," Klein said.

He added that anyone who wants cat-like pupils, irises that look like mini-eight balls or contacts in any colour of the rainbow can get and wear them safely with a doctor's help.