Impotence pill `can damage eyesight'

VIAGRA, the new drug for impotence can cause damage to eyesight for those who over-use it, scientists have claimed.

In sufficient doses it could cause damage to the retina of the eye, the New Scientist magazine reports today.

The erection pill has taken America by storm. Less than three weeks after its launch, doctors in the United States had written an unprecedented 113,000 prescriptions for Viagra.

The pill even received an endorsement from the former presidential candidate Bob Dole, and the drug looks set to have the same effect in Britain.

But it is known to have a side-effect that causes "blue vision" and some eye experts fear that Viagra may do more than that, even in sufficient doses damaging 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.

The drug is thought to mimic a condition where levels of phosphodiesterase are abnormal.

"This has ophthalmologists worried, because people with congenitally abnormal phosphodiesterase suffer irreversible damage to their retinas over time," said the report in the New Scientist.

The American Academy of Ophthalmologists is now pressing Pfizer, the drug company which manufactures Viagra, to conduct more studies. Michael Marmor, an eye specialist at Stanford University in California, told the magazine: "The company has not measured the electrical activity of the cone cells in the long term."

But Pfizer said that rigorous tests at doses well above the recommended level had shown no clinically significant effect on vision in either the short term, or the long term.

There are also already fears that some men wanting to reclaim youthful vigour are taking higher than recommended doses despite their doctors' warnings.

In the clinical trials which convinced the American Food and Drug Administration to approve Viagra, the "magic bullet" drug quadrupled men's success at having sexual intercourse and significantly improved the quality of their erections. In one study, men receiving 100 milligrams of Viagra, the highest recommended dose, doubled their frequency of erections.

But one sexual health expert told New Scientist that the reality of Viagra's performance did not match the hype.

However, James Barada, of the Center for Male Sexual Health in Albany, New York, said that many of the men in the trials had achieved intercourse in the previous three months and so were not clinically impotent. He claimed that only one-third of men who were genuinely impotent, were able to have intercourse after taking the drug.

Mr Barada, who has written more than 150 prescriptions for Viagra, said: "I consider them Viagra failures. You don't take a drug just because it helps a little bit."

Suggested Topics
Start your day with The Independent, sign up for daily news emails
Have you tried new the Independent Digital Edition apps?
News
ebooksAn unforgettable anthology of contemporary reportage
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Recruitment Genius: New Business Development Manager / Sales - UK New Business

£24000 - £36000 per annum: Recruitment Genius: Join a fast growing, UK based I...

MBDA UK Ltd: Mission Planning and Control Solutions Systems Engineer

Competitive salary & benefits: MBDA UK Ltd: What’s the opportunity? A pro-act...

MBDA UK Ltd: System Design Capability

Competitive salary & benefits: MBDA UK Ltd: What’s the opportunity? The small...

Recruitment Genius: Time Served Fabricator / Welders - Immediate Start

£25000 - £35000 per annum: Recruitment Genius: Fabricator welder required for ...

Day In a Page

Sepp Blatter resignation: The beginning of Fifa's long road to reform?

Does Blatter's departure mean Fifa will automatically clean up its act?

Don't bet on it, says Tom Peck
Charles Kennedy: The baby of the House who grew into a Lib Dem giant

The baby of the House who grew into a Lib Dem giant

Charles Kennedy was consistently a man of the centre-left, dedicated to social justice, but was also a champion of liberty and an opponent of the nanny-state, says Baroness Williams
Syria civil war: The harrowing testament of a five-year-old victim of this endless conflict

The harrowing testament of a five-year-old victim of Syria's endless civil war

Sahar Qanbar lost her mother and brother as civilians and government soldiers fought side by side after being surrounded by brutal Islamist fighters. Robert Fisk visited her
The future of songwriting: How streaming is changing everything we know about making music

The future of songwriting

How streaming is changing everything we know about making music
William Shemin and Henry Johnson: Jewish and black soldiers receive World War I Medal of Honor amid claims of discrimination

Recognition at long last

Jewish and black soldiers who fought in WWI finally receive medals after claims of discrimination
Beating obesity: The new pacemaker which helps over-eaters

Beating obesity

The new pacemaker which helps over-eaters
9 best women's festival waterproofs

Ready for rain: 9 best women's festival waterproofs

These are the macs to keep your denim dry and your hair frizz-free(ish)
Cycling World Hour Record: Nervous Sir Bradley Wiggins ready for pain as he prepares to go distance

Wiggins worried

Nervous Sir Bradley ready for pain as he prepares to attempt cycling's World Hour Record
Liverpool close in on Milner signing

Liverpool close in on Milner signing

Reds baulk at Christian Benteke £32.5m release clause
On your feet! Spending at least two hours a day standing reduces the risk of heart attacks, cancer and diabetes, according to new research

On your feet!

Spending half the day standing 'reduces risk of heart attacks and cancer'
With scores of surgeries closing, what hope is there for the David Cameron's promise of 5,000 more GPs and a 24/7 NHS?

The big NHS question

Why are there so few new GPs when so many want to study medicine?
Big knickers are back: Thongs ain't what they used to be

Thongs ain't what they used to be

Big knickers are back
Thurston Moore interview

Thurston Moore interview

On living in London, Sonic Youth and musical memoirs
In full bloom

In full bloom

Floral print womenswear
From leading man to Elephant Man, Bradley Cooper is terrific

From leading man to Elephant Man

Bradley Cooper is terrific