The Association of Optometrists, an organization representing over 30,000 optometrists in the United Kingdom, said around Halloween many of its members treat patients for eye-related complications resulting from novelty contact lenses.
'Most of the patients haven't been shown how to look after their cosmetic lenses or their eyes properly.
"Each year we treat patients, including children under 16, who have developed eye conditions after wearing cosmetic contact lenses", Bardul Hussain, consultant ophthalmic surgeon at Moorfields eye hospital, said to various media outlets.
The practice has led to a spike in people in the United Kingdom seeking medical help around the Halloween period, which is why health authorities are now warning against wearing the coloured contacts. "Not knowing the basics of using contact lenses safely can put you at higher risk of developing painful eye injuries, infections and in the worst cases, permanent sight loss", he said.
A fan with colored contact lenses poses for a picture at 2014 New York Comic Con (October 10, 2015).
"This can expose the eye to organisms that can cause nasty infections, which in extreme cases can result in permanently impaired, or loss of, vision".
Experts said people could suffer vision loss or infection from the lenses, with an increased risk for those who share them with friends, wear the same pair year after year or store them in water.
The coloured cosmetic lenses are often illegally sold online, in shops and on market stalls, rather than by a registered optician or doctor.
He added: 'The cornea, the clear window at the front of the eye, is delicate and can be scratched easily by inexperienced contact lens wearers. These lenses are known as zero-powered lenses because they do nothing to correct the wearer's eyesight.
Vicky McDermott, chief executive of the General Optical Council, said: 'When worn safely, the risks associated with cosmetic contact lenses are low.