American teenagers are potentially hurting their eyesight by wearing a controversial contact lens that makes their eyes look bigger.

Lady Gaga started the trend after her music video for Bad Romance came out last year.

The video shows the singer's eyes digitally altered to make them look bolder and larger.

Several Asian companies claim to have achieved a similar effect with contact lenses that give the same look.

The product is known as “circle lenses”. It covers part of the white area in the eye to make the pupil appear bigger.

The lenses are illegal in the US because they have not been approved by the Food and Drug Administration, but can be bought online from foreign sites.

Teenage girls have been buying the contacts from South Korea and Japan, where they are perfectly legal.

The lenses come in various colors, including bright pink and red. They cost around $20.

Eye experts are worried that the non-existant quality control will lead to problems such as eye infections, vision damage and potential loss of vision.

DR Assumpta Madu, from the Montefiore Medical Center in New York, said, “there literally is potential for somebody to lose their vision within 24 hours from an infection."

The Circle Lenses are available to correct poor eyesight, or without prescription to use as a fashionable accessory.

Doctors warn that contact lenses should only be acquired after an optician has approved a prescription.

One company that sells them online is called CircleLens2U. It claims that the product is sade and has been approved by health officials in Asia.

The company said that "the lens itself doesn't have any quality problem. They are just like any normal soft color contact lenses you could found (sic) on the market."

the YouTube video on how to get the look made famous in Bad Romance has had more than 11 million views.

Chantal George, 19, of Pennsylvania, has been wearing the contacts for almost two years.

"As of now, I have 15 pairs", she said. "It's like wearing a new shade of make-up, or a new outfit.

"I feel like I'm popping in terms of my look for the day."

Chantal said that she is not worried about wearing them and will continue to encourage her friends to wear them as well.

"I say these are like any other contact lenses. They need to have care taken of them, they need not to be worn too often or for too long.

"And they're just colored lenses - just not made in the United States."