They know that smoking causes lung cancer and is a risk factor for stroke and heart disease but only a small portion know it is linked to age related macular degeneration -- the leading cause of blindness in the elderly.

"The vast majority, over 90 percent, didn't know it," said Dr Simon Kelly, an ophthalmologist at Bolton Hospitals NHS Trust in northern England,

"The majority of adults don't know this either," he added.

Kelly and his team believe increasing knowledge about the link between smoking and blindness would provide more incentive for both teenagers and adults to give up smoking.

In a study published online by The British Journal of Ophthalmology the researchers questioned 260 teenagers to gauge their knowledge of the dangers of smoking. They were also asked to rank their fears about various diseases.

Nearly 30 percent of the 16-18 year-olds realized smoking was linked to heart disease but only 5 percent correctly identified smoking as a cause of blindness.

Kelly said most of the teens were sufficiently shocked and scared by the link to age related macular degeneration that that they were willing to quit.

Macular degeneration is a chronic, progressive disorder of the central portion of the retina, which is known as the macula. It causes loss of central vision and blindness.

Age and genetics are key risk factors for the illness. But chemicals in cigarettes affect the nutrition and the metabolism of the macula, according to Kelly.

NEW WARNING ON CIGARETTE PACKETS

The researchers believe there is enough evidence of the link between smoking and macular degeneration for warnings to be added to cigarettes.

"We are calling for the message 'Smoking causes blindness' to go on cigarette packages. The message has been used in Australia on both cigarette packages and TV campaigns and it has been found to be highly effective," said Kelly.

He added that the Royal College of Ophthalmologists and the Royal National Institute of the Blind and other organizations support the call for new warnings.

But the messages that can appear on cigarettes in Europe are governed by European Union rules which requires consensus throughout Europe.

Kelly said teenagers are a hard to reach audience in health-promotion terms because they believe they are invincible. They don't worry about lung cancer or heart disease.

"When patients are told smoking is damaging their eyes, in my experience, they are usually keen to quit smoking," he added.