A drug to treat a common eye disease has produced promising results in a major trial, researchers have said.
Wet AMD affects the vision of about seven million people worldwide
Macugen, known technically as pegaptanib, is the first drug to target the underlying cause of the wet form of age-related macular degeneration (AMD).
It works by stopping the formation of blood vessels that leak into the eye eventually destroying central vision.
The research, sponsored by the drug manufacturers Pfizer, is published in the New England Journal of Medicine.
AMD is the leading cause of severe vision loss in patients over the age of 50 in the developed world.
Worldwide, approximately seven million people suffer from severe visual impairment caused by wet AMD
The condition is caused by the growth of new blood vessels under the centre of the retina, also known as the macula, which houses the cells that react to light.
These blood vessels can leak fluid, causing scar tissue to form and destroying central vision in a period of between two months and three years.
There are three subtypes of wet AMD: predominantly classic, minimally classic and occult.
Macugen has been shown to be effective in treating all three.
It works by blocking a protein called a vascular endothelial growth factor, which plays a crucial role both in the formation of new blood vessels, and their tendency to leak.
In the latest research patients given Macugen showed a significantly reduced risk of moderate and severe vision loss. Some maintained, or even improved their vision.
There were few side effects, although a third of patients reported some eye pain.
Gerrard Grace, chair of the charity AMD Alliance International, said: "With an ageing global population, age-related macular degeneration has become the most pressing vision-related public health problem in the developed world.
"Macugen will provide a much-needed therapy for millions of people whose independence and quality of life may be threatened by debilitating vision loss."
Tom Bremridge, chief executive of the Macular Disease Society, told the BBC News website that AMD was currently treated with a combination of a drug and laser treatment called photodynamic therapy.
However, the National Institute for Clinical Excellence has decided that at present this treatment should only be available to people with one type of wet AMD.
Mr Bremridge said: "The results with the new drug are as good, if not better, than those produced by photodynamic therapy."
He stressed Macugen would only work for people whose AMD was still at a relatively early stage of development.
Macugen is currently being evaluated by European Medicines Evaluation Agency (EMEA).
The US Food and Drug Administration approved the medicine as a treatment for wet AMD last month.