The FDA issued a message via Twitter to fans of the young adult "Twilight" series attending the official convention in San Antonio in August, cautioning them against non-regulated custom contact lenses that let them imitate their "fave vampire."

"Want 2 look like your fave vampire?" the federal watchdog agency tweeted. "C an eye doctor before buying costume/fashion lenses."

The tweet included a link to an FDA one-pager on the dangers of decorative contact lenses, which can cause allergic reactions, cuts or scratches on the cornea, eye infections, decreased vision or even blindness.

The message was targeted to the moderators of the upcoming "The Twilight Saga Official Convention," which will tour through Texas, Michigan and New Jersey in August, September and October.

The convention features a costume competition that encourages fans to "come dressed as their favorite characters from The Twilight Saga," a story about teenage girl who finds herself caught between the worlds of vampires and werewolves.

"Just like regular contact lenses you should never buy contact lenses from a street vendor, a beauty supply store, lea market, novelty store or Halloween store and you should always have a prescription. medical devices more quickly and inform patients when their safety is at risk," the FDA warned.

Decorative lenses are frequently available without a prescription from internet sellers, flea markets, novelty stores, conventions or even from street vendors, but those products aren’t regulated or monitored for safety, the agency said.

"It’s very important that you only buy contact lenses from a company that sells FDA-cleared or approved contact lenses and requires you to provide a prescription," according to the report.