Halloween may be the time to sport a scary costume, but federal agencies warn of equally terrifying dangers associated with decorative contact lenses that some wear for the spooky celebration.

The U.S. Food and Drug Administration and two other agencies have issued a warning against buying contact lenses sold at Halloween shops, novelty stores and beauty salons, citing that many sell illegal lenses that can cause permanent eye damage.

"Even though Halloween approaches, consumers shouldn't let a good deal or great costume blind them to the dangers of counterfeit decorative contact lenses," Homeland Security Investigations Executive Associate Director James Dinkins said in a statement. "What's truly scary is the damage these counterfeit lenses can do to your eyes for a lifetime."

The warning comes at a time where U.S. Immigration and Customs Enforcement, the FDA, Homeland Security Investigations and U.S. Customs and Border Protection have been coordinating to seize counterfeit lenses in an operation known as “Operation Double Vision.”

By law, contact lenses require a prescription, which ensures the lens fits properly to an individual’s eyes. Doctors warn that contact lenses sold without a prescription from unauthorized sellers, which can cost as little as $20, may cause permanent damage.

"Contact lenses are a medical device and it is smart to purchase them from a medical professional who will fit them to your eye," Dr. Glenda Brown, president and a member of the Georgia Optometric Association said. "Consumers who buy lenses that were manufactured and sold illegally can experience infections, corneal ulcers and even blindness."

Novelty lenses, including anime ones and circle lenses that give the wearer a doll-like look, are not approved by the FDA. All lenses should be bought from legitimate stores and websites that require a prescription given by an eye doctor.

"Our concern is that consumers who buy and use decorative contact lenses without a valid prescription can run significant risks of eye injuries, including blindness," said John Roth, director of FDA's Office of Criminal Investigations. "It is always better to involve a qualified eye care professional and protect your vision."

The American Academy of Ophthalmology issued a similar statement on the dangers of costume contact lenses earlier this month.

The practice of selling costume contact lenses without a prescription has been illegal since 2005. When contact lenses are not made according to FDA standards, the devices carry a risk of causing serious eye injuries such as cuts, open sores, corneal abrasions and ulcers. Some require surgery or transplants and cause vision loss. One study found a person using cosmetic contact lenses was 16 times more likely to develop keratitis than those who didn’t wear novelty lenses.

"What happens to people's eyes after just one evening of wearing non-prescription costume contact lenses is tragic," Thomas Steinemann, M.D., professor of ophthalmology, MetroHealth Medical Center and Case Western Reserve University in Cleveland, said in a statement. “I understand how tempting it is to dress up your eyes on Halloween without a prescription and using over-the-counter lenses, but people should not let one night of fun ruin their vision for a lifetime."

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