Think twice before buying that pair of spooky eye contacts for Halloween without a prescription.

Sure, they can give you cat eyes or perfectly complement your ghastly attire. But they can come at a high cost: permanent eye damage, experts say.

The FDA recently released a friendly reminder on how to safely buy the lenses with a less welcoming list of ailments Halloween goers experience from sporting non-prescription decorative eye contacts on the holiday.

NEWS: Cell Phone App Offers Eye Prescriptions

These types of contacts aren’t designed to improve a person’s vision, but rather to change how the eyes look. Like other contacts, decorative lenses need to be sized by an eye doctor to fit well. Although it might not be the first thing on Halloween shoppers’ minds, decorative contacts should be purchased with a prescription.

In fact, anyone selling the lenses without a prescription is breaking the law, says the FDA, considering the fact that regular contacts and decorative types fall under FDA-regulated medical devices.

Buying the creepy eyes from unregulated vendors might save money, but it’s illegal business and increases a person’s risk of eye damage. Common ailments include scratched corneas (the outer portion of the eyeball), ulcers, pink eye and some vision loss. In some cases, people become blind.

SCIENCE CHANNEL: Ghost Hunting Investigation

Not washing the lenses or buying a size that doesn’t fit usually spurs infection.

Most doctors can accommodate decorative prescriptions, but few will give into recommending the large circle lenses that recreate large eyes seen in anime cartoons Clinics often subject people to an eye exam before signing off on Halloween contacts.

SLIDESHOW: How History Shaped Halloween

It’s best to avoid places that don’t ask you for a prescription, including seasonal Halloween stores and the Internet. Doctors also recommend getting medical attention right away if contacts are appearing to cause pain or problems.

The American Academy of Ophthalmology’s educational program released a video (using a more scare-tactic approach) that details a young woman’s experience after using non-prescription lenses for Halloween.