Viagra 'may cause blindness': Ingredient in the drug can permanently affect sight, doctors warn

Viagra could cause blindness in men with eye problems, and even those with seemingly normal vision, a new study has found.

Australian researchers say an ingredient in anti-impotence drugs may permanently affect the vision of men with an inherited eye condition.

It could also affect those with normal sight who carry one gene which is linked with developing eye problems.

One theory is that erectile dysfunction drugs may obstruct an enzyme which is important for transmitting light signals from the retina to the brain.

It is already known that sildenafil, the active ingredient in the erectile dysfunction medication, can cause temporary vision problems in some healthy people.

Doctors have now warned it could also cause permanent damage to the eyes of people retinitis pigmentosa.

People with normal sight that carry the gene for the condition may also be at risk, experts warn.