An increasing number of teenagers are seeking treatment for inflammation of the cornea due to use of contact lenses without prescription, said Associate Professor Dr Bariah Mohd Ali, contact lens consultant at UKM's Faculty of Health Sciences.
"We are seeing more and more cases of teenagers with keratitis related to contact lens wear in our clinic. Contact lenses cannot be used without prescription from optometrists or ophthalmologists.
"This is because they are medical devices that can only be handled by trained professionals.
"A proper eye examination is needed prior to wearing contact lenses. Also important is proper instructions on lens maintenance and hygiene.
"These teens don't realise that they are are taking a huge risk and may lose their vision permanently if they wear lenses bought from street vendors or online sources.
"Wrongly fit contact lenses can easily cause corneal oedema and infections that leads to blindness."
She said popular among Malaysian teens was the circle lens, a type of cosmetic contact lens that is developed to enhance the iris diameter. The lens has a tinted outer ring overlapping the white of the eye, making the iris appear much larger.
"The normal iris diameter is around 12mm and the circle lens can enhance it to between 14-16mm. In Asia, a larger iris diameter is associated with beauty and hence the circle lens has become very popular.
"This type of lens can be easily bought from street and online vendors. However, there is no guarantee on the quality of these lenses."
A study conducted in the United States, she said, found that consumers who bought contact lenses from sources other than their eyecare practitioner were less likely to comply with good eyecare practices.
Another research in Australia showed a higher risk of developing microbial keratitis, a rare, but serious infection, with lenses bought online.
The research also found that the risk associated with online or mail order purchase of lenses was 4.76 times higher than when lenses were bought from optometrists.
Although there is no age limit for children to start wearing lenses, Dr Bariah stressed that it must always be done with proper consultation to avoid future complications.
"Contact lenses are prescribed for children for therapeutic and cosmetic purposes, that includes vision improvement, part of amblyopia therapy (decrease of vision), aniridia (absence of the iris), aphakia (absence of the lens of the eye) and to mask corneal scars.
"Therefore, contact lenses are safe for children provided it is prescribed by optometrists or ophthalmologists."