A disease which robs people of their sight in later life is threatening to become a 21st century scourge during the next 20 years, it is claimed.

Age related Macular Degeneration is already the UK's leading cause of blindness in people over the age of 50 - but fewer than 2 per cent of the public are aware that the condition exists.

The disease causes a complete loss of central vision, and distortion to peripheral sight.

Evidence indicates that cases of AMD are on the increase, and the disease is spreading from western countries to the rest of the world.

In the UK the incidence of AMD has doubled since the 1950s. Experts predict that the number of victims will triple in the next 25 years.

The most severe form of the disease, known as "wet" AMD, already claims an estimated 16,000 new victims each year in England and Wales.

The impact of AMD is expected to increase greatly with the demographic shift towards an older population.

Unknown environmental factors possibly linked to western lifestyle and diet are also thought to be worsening the problem. As a result the disease is establishing itself for the first time in countries such as Japan, where it was unknown 30 years ago.

Former GP Dr Bob Thompson, who became a young victim of the disease at 48, and now chairs the patients' organisation AMD Alliance International, said: "We are looking at a major forthcoming problem. We're sitting on a demographic time-bomb here."

Dr Thompson was speaking at a weekend conference in Lausanne, Switzerland which is aimed at introducing ophthalmic specialists to a new treatment for "wet" AMD.

The disease is caused by rogue blood vessels which sprout under the retina and destroy the photoreceptor cells responsible for vision. There is no known cure.

The new treatment, called photodynamic therapy, uses laser light to activate a drug which seals the blood vessels and stops them doing any further damage. Although it cannot reverse AMD, it prevents the disease progressing.

At the meeting results were announced of an international trial of the Visudyne therapy developed by Ciba Vision, a subsidiary of pharmaceutical giant Novartis and the Canadian company QLT PhotoTherapeutics Inc.

More than 600 patients from 22 centres in the United States, Canada and Europe took part in the trial over two years. Two centres were at St Paul's Eye Unit, Royal Liverpool University Hospital, and Aberdeen Royal Infirmary.

The study found that in 61 per cent of patients returning for a check-up after 12 months vision had improved or stabilised. The benefit was sustained over the second year.

The treatment costs about £3,000 per year per patient. But a study in Switzerland, where it has already been approved by the regulatory authorities, showed that the cost equalled that of assistance and support needed by someone who was left untreated.

Straight lines appearing bent, wavy or fuzzy, and blind spots, are the first signs of AMD.

Dr Thompson said: "I was a GP working happily in North Yorkshire. Then I noticed a disturbance to my vision, and within 18 months I was legally blind. It's a devastating thing to happen."