The outspoken U2 main man says he has suffered from the eye condition glaucoma for over 20 years.

U2 frontman Bono has made a candid revelation on the reason why he is never seen without his tradenark sunglasses indoors - he suffers from glaucoma.

During the filming of BBC One's Graham Norton show, the singer confirmed that he's suffered from the chronic eye condition for the past 20 years.

"This is a good place to explain to people that I've had glaucoma for the last 20 years. I have good treatments and I am going to be fine," he said on the show. Adding: "You're not going to get this out of your head now and you will be saying, 'Ah, poor old blind Bono.'"

The illness is caused by a build-up of pressure in the eye socket, which leads to sensitivity to light and can result in blindness if left untreated.

U2 recently gave away their latest album 'Songs Of Innocence' for free via iTunes. Earlier this week, Bono apologised for the giveaway, admitting to a "drop of megalomania".

Iggy Pop was amongst many critics of the marketing ploy, saying that the band were trying to force their music upon consumers.