They’re a popular novelty item for Halloween costumes, but coloured contact lenses could leave you blind, eye doctors have warned.

If bought online or from a market stall, it’s possible that the lenses could give you an infection as they may not have been medically-approved.

An esteemed eye surgeon at Moorfields Eye Hospital NHS Foundation Trust in London has said that he sees an increasing number of emergency lens-related cases during Halloween, reports BBC.

Badrul Hussain is treating more and more children under the age of 16 who have developed infections after wearing novelty contact lenses.

“Some of the cases we see, like patients sharing lenses with friends, wearing the same pair year after year well past the expiry date, and storing them in tap water, have devastating effects,” he said.

Hussain stresses the importance of lens after-care in avoiding infection, explaining that most novelty lens brands don’t offer substantial medical advice, which puts wearers at a higher risk of developing injuries and possible sight loss.

The cornea area of the eye is particularly vulnerable and can be easily scratched or impaired if a lens is inserted incorrectly, he added.

Novelty lenses are widely available online, starting at around £5.99 per pair.

They are increasingly popular around October time, as people start planning their fancy dress outfits for Halloween parties.

The British Contact Lens Association (BCLA) issued a warning last year that the lenses could result in sight loss.

“Wearing fancy lenses might make you look cool for one night on Halloween but losing your sight could be a lifelong horror story,” said Brian Tompkins, president of the BCLA.