Cocktail lenses - cosmetic contact lenses with no optical power - are the newest thing on the dancefloor and the catwalk. The designer Alexander McQueen has featured them on his models and they are attracting a growing following. Like all fashion crazes, they come with their own health warning.
A loophole in the law means cocktail lenses can be sold anywhere - across the counter, on market stalls or by mail order. There is no optical problem they correct, so there is no need for an optician. This means that there is nobody to check that they fit properly, no inspection of the health of the eye and no advice on cleaning and maintenance.
Worse, easy access brings an easy-going attitude to their use. Teenagers are said to be swapping lenses to match their mood or outfit heedless of the risk of cross infection. Bugs present in one person's eye, which cause no problem, may flare up into a nasty infection when transferred into the different immunological environment of someone else's eye.
Theoretically there is even a risk that HIV could be transferred this way. The virus is transmitted in bodily fluids and may be present in tears, although there are no recorded instances of infection by this route.
Consultant ophthalmologists fear that laxity in the supervision of contact lens-wearers will result in more infections which, though rare, can have devastating consequences. About five in every 10,000 wearers of soft lenses, the most popular kind, require treatment each year, but this rises to 20 per 10,000 for extended-wear lenses which may be left in day and night for up to three months.
Infection and oxygen deprivation are the principal problems for contact lens-wearers. The soft lenses cover most of the cornea (the transparent surface of the eye) preventing air getting to it. An ill-fitting lens can aggravate the problem of oxygen deprivation and in severe cases where the problem is prolonged, blood vessels can grow into the cornea, interfering with vision. Hard lenses, which are smaller and sit over the pupil, have fewer problems with oxygen deprivation and lower infection rates, because less of the eye is covered.
Professor Roger Buckley, chairman of the contact lens committee of the General Optical Council said: "We know they can be just as harmful to the eye as ordinary contact lenses, but the risks are greater because they are not fitted and no instruction is given in cleaning and maintenance."
Handling lenses with dirty hands and failing to clean them properly is the quickest way to guarantee an infection. All the usual suspect bugs are capable of doing damage - staphylococcus, pneumococcus, pseudomonas. One of the most serious is acanthamoeba keratitis which causes scarring of the cornea and can result in the need for a corneal graft.
The bigger the surface of the eye that is covered by the lens, the easier it is for protein to build up on it, forming a biofilm in which bugs can thrive. The best defence against infection, therefore, is frequent cleaning and replacement of lenses.
David Gartry, consultant ophthalmologist at Moorfields Eye hospital, in London, said: "Acanthamoeba infections have become more prevalent over the past 15 years. It is a bug that forms cysts which are very resistant to being killed, so it is ubiquitous - in taps, shower heads and swimming pools. Cleaning and replacing lenses is essential. Swapping them is an awful thing to do."
Doctors and opticians are concerned about the growth of mail-order sales of contact lenses, whether cosmetic or conventional, which reduce the likelihood of customers' eyes being checked and the right advice given. One mail-order firm, Vision Direct, was successfully prosecuted by the General Optical Council this month for failing to provide proper supervision of the sale of the lenses by an optician.
Mr Gartry said "I am horrified by the idea of selling a medical appliance by mail order. Patients may end up in casualty if they are not followed up."