Online auction company eBay is facing court action over claims it allowed contact lenses to be sold on the site.
eBay deny the charges
The General Optical Council claims people buying lenses online risk serious eye problems because they do not receive the necessary checks.
By law, lenses must be sold by a registered optician or doctor.
But eBay said contact lenses were among items it did not permit to be sold on the site, and any listings it becomes aware of are removed.
The GOC says there were over 200 contact lens entries on eBay two days ago, but that these have since been taken down.
If found guilty in the court case, the company could face a fine of up to £2,500 per charge.
The GOC, which regulates the work of all optometrists and opticians in the UK, has issued eBay with a summons over the alleged sales.
Nathan Efron, a GOC member and professor of optometry at Manchester University, said: "Lenses sit directly on the eye, so even if they feel fine to the wearer, there is a risk of irritation and infection.
"These kind of problems could result in a wearer becoming intolerant, and not being able to wear contacts again.
"However, in a worst case scenario, it could lead to vision loss and blindness.
"So it is incredibly important to have lenses fitted by a qualified professional."
The rules apply to fashion lenses, such as those which give the wearer a different eye colour, as well as those prescribed to correct sight problems.
The GOC says it alerted eBay to its concerns last November.
GOC registrar Peter Coe said: "Given the company's continued failure to deal with the problem, a summons was issued in August this year.
"We very much regret that it has been necessary to take legal action in this case."
But in a statement, eBay UK Ltd strongly rejected the GOC's comments.
It added: "If eBay is made aware of any listings offering contact lenses, these listings are promptly taken down.
eBay said its listing policy clearly stated that controlled drugs or items which required prescriptions from licensed practitioners such as doctors, dentists or opticians were not permitted.
"This includes, but is not limited to, prescription drugs, contact lenses, and prescription eyewear," eBay UK Ltd said.
The rules governing the sale of contact lenses are set out in the Opticians Act 1989, which was amended in June this year.
It states that: "a person shall not sell any optical appliance unless the sale is effected by or under the supervision of a registered medical practitioner or registered optician."
The case will be heard at the City of London Magistrates' Court on London on October 10.