Tests by researchers at Colombia University in New York suggest the anti-impotence drug could halt age-related macular degeneration, or AMD.About 600,000 Brits are understood to have suffered loss of sight as a result of the condition, making it the UK's leading cause of blindness. 
                Five elderly patients with AMD took part in the US study. They were given two Viagra or Sildenafil pills every a day for two years.The results showed the drug, which this year became available over the counter in Britain, stopped the condition in its tracks for four participants and significantly improved the eyesight of one.

                 Researchers said: "Viagra offers significant potential for vision retention and recovery. It is notable that patients remained visually stable and there was a significant improvement in vision in one participant."Dry AMD, the slow acting form of the disease that takes several years to manifest, affects around 90 per cent of cases in the UK.

                      The rest suffer the more rapid wet AMD, which can cause blindness in as little as three months.Dry AMD usually develops after the age of 50 and is caused by the growth of new blood vessels over the macula, a small oval-shaped area at the back of the eye needed to pick out visual details clearly.Fluid leaks from the blood vessels, causing scar tissue to form and ruin vision in the centre of the eye.Sufferers of the condition find it difficult to read, watch television and even recognise faces.

             Other research has found that AMD is partyl caused by resduced blood flow to vital parts of eye tissue in front of the retina.The latest results, published in the journal of Ophthalmologica, compliment earlier studies suggested Viagra can improve blood flow.