Colourful or unusual-looking contact lenses are popular at Halloween, but they could harm your eyes, vision experts warn.

“Decorative contact lenses may seem like a fun costume accessory, but if you’re not careful, they can cause serious eye and vision problems,” said Samuel Pierce, president of the American Optometric Association (AOA).

“Many people mistakenly believe they don’t need a prescription for decorative contact lenses. It’s extremely important that anyone desiring to wear contact lenses for any reason get an eye exam from a doctor of optometry and only wear contact lenses, with or without vision correction, that have been properly fitted,” Pierce said.

Be careful where you buy novelty contact lenses

There is growing concern about sales of illegal decorative contact lenses online and at locations such as costume shops and gas stations.

A recent AOA survey found that 26% of Americans who have worn decorative contact lenses bought them without a prescription from a source other than an eye doctor.

Illegally purchased contact lenses can cause bacterial infections, allergic reactions and even permanent vision loss.

To combat this problem, the AOA is conducting its annual “31 in 31” campaign, in which it sends letters to 31 online and other sellers who have been reported to the AOA as conducting illegal contact lens sales.

“Unfortunately, far too many companies are breaking the rules… to make sales and profits,” Pierce said in an AOA news release.

“Through our ’31 in 31′ campaign, we strongly urge these companies to reverse their policies of illegally distributing contact lenses without valid prescriptions in violation of federal law,” he added. “These sales potentially put patients at risk for sight-threatening complications. It’s a matter of public safety.”

More information

The US Centers for Disease Control and Prevention has more on contact lenses.