U2's Bono revealed he always wears dark sunglasses as he suffers from Glaucoma

U2 frontman Bono has revealed that the reason he's always seen in his dark glasses is because he suffers from glaucoma.

The star said he has had the condition - a build-up of pressure in the eyeball, which can damage the optic nerve and lead to blindness if not treated - for around two decades.

The musician made the admission on The Graham Norton Show, when Norton asked if he ever removes his glasses. The show will air tonight on BBC1.

"This is a good place to explain to people that I've had glaucoma for the last 20 years," said Bono.

"I have good treatments and I am going to be fine."

He added with good humour: "You're not going to get this out of your head now and you will be saying 'Ah, poor old blind Bono.'"

He had previously said he wore his signature shades because he was “very sensitive eyes to light”.

"If somebody takes my photograph, I will see the flash for the rest of the day," he told Rolling Stone in 2005. "My right eye swells up."

The Irish band were on the show to promote their new album, Songs Of Innocence, which was released commercially this week after previously being given away to half a billion iTunes customers, a controversial move which upset some people who said they did not want it automatically added to their music libraries.