EL PASO, Texas -

El Pasoans still on the prowl for the perfect Halloween costume -- beware. The wrong getup could make some trick-or-treaters go blind, according to federal authorities.

A number of law enforcement agencies this week seized counterfeit color contact lenses from street vendors in downtown El Paso and on Craigslist. The accessory is a costume staple, agents said.

"Poor fit can cause serious eye damage, including scratches on the cornea, corneal infections, conjunctivitus -- also known as pink eye -- decreased vision, or even blindness," said Special Agent Dennis Ulrich of Homeland Security Investigations.

In some cases, the lenses can adhere to the eye and need to be surgically removed, Ulrich said.

Operation Double Vision involved agents from U.S. Immigration and Customs Enforcement, Homeland Security Investigations, the Food and Drug Administration, and other agencies.

Buying or selling corrective lenses without a prescription is illegal, Ulrich said. Black market vendors sell them for roughly $20 a pair, but the only way to legally obtain contacts is through a medical professional.

"We did check with some of the larger Halloween stores, who advised us immediately that they do not sell these contact lenses, because they do require a prescription, and they are not licensed to carry them," Ulrich said.

Agents have made no arrests. The investigation is still under way, and it may result in criminal charges, Ulrich said.

"A lifetime of good vision," said Dr. Glenda Brown, president of the Georgia Optometric Association, "is so much more important than a cheap Halloween accessory."