London - Viagra, the new drug for impotence, could damage the eyesight of men who get too carried away with it, experts have warned.
The erection pill that has taken the US by storm is known to have a side-effect that causes "blue vision". But some eye experts fear Viagra may do more than give you a blue view - insufficient doses of it could damage the retina.
Viagra works by inhibiting an enzyme called phosphodiesterase, which allows more blood to flow into the penis. A similar enzyme exists in the cone cells responsible for colour vision in the retina. It is the effect on this enzyme that leads to a perception of the colour blue, and which is concerning eye specialists.
New Scientist reported yesterday: "This has ophthalmologists worried, because people with congenitally abnormal phosphodiesterase suffer irreversible damage to their retinas over time."
Pfizer, the drug company which produces Viagra, said rigorous tests at doses well above the recommended level had shown no clinically significant short-term or long-term effect on vision. But there are fears that some men are already taking doses higher than recommended despite their doctors' warnings.