People are being urged not to use "novelty" contact lenses this Halloween, which can lead to issues ranging from mild discomfort up to permanent vision loss.
Health regulator CORU, which regulates Health and Social Care Professionals, issued a warning to children, teenagers and adults against the use of the lenses.
"Novelty" contact lenses are often used as part of Halloween costumes or fancy dress.
Declan Hovenden, who is a member of CORU's Optical Registration Board and Head of Optometry at TU Dublin, said the novelty lenses are "extremely risky".
Speaking to RTÉ's Drivetime, Mr Hovenden said: "Risks range from mild, such as irritation or discomfort, to much more severe up to and including permanent vision loss."
Listen: Regulator warns against 'novelty' contact lenses
"More severe risks would normally be associated with infection of the cornea that, if untreated, could lead to significant and permanent corneal scarring, resulting in significant vision impairment, vision loss, or even blindness," he added.
Mr Hovenden said that while some of the lenses may be corrective as opposed to just cosmetic, questions relating to quality assurance remain.
"Approved cosmetic contact lenses that can be supplied by registered optometrists or opticians can come in both prescription forms, so with optical correction or without optical correction," he said.
"The quality assurance around these products that are not approved or approved for use or sale in Ireland, we can't be sure what standards that they're at in terms of the optical correction, nor in terms of the materials that are being used."
Mr Hovenden said that people may not be aware of the risks associated with novelty contact lenses.
"What they may not be aware of is that the materials in these lenses are very different, or can be very different," he said.
He said the substances that are used in the dyes can cause allergies or increase the risk of infection.
"We don't know what conditions they're manufactured under and we don't know how they've been stored, so we don’t know if they’re coming in sterile in the first place.
"There are lots of unknown risks that might not be apparent to an inexperienced user or even an experienced user of regular contact lenses," he added.
Mr Hovenden encouraged anyone who is considering wearing the novelty lenses this Halloween to get them from an approved source.
"If children, teenagers, adults or anybody wants to wear coloured contact lenses, the approved lenses are available from optometrists or opticians," he said.
"These can be fitted by eye care professionals."
Mr Hovenden said those fitted by professionals are done so correctly and are suitable for the eye.
He said they can identify if the patient is suitable for them, so that they can be worn as safely as possible.
"But buying them off the internet, not knowing where they've come from, not knowing what they're made of or how they've been stored, that's where the risks lie," he added.
