In Friday night's episode of The Graham Norton Show on BBC One, U2's Bono explains that he has been living with the eye condition glaucoma for 20 years.

During the interview, Norton asks the singer whether he ever takes off his trademark sunglasses, to which Bono replies: "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 says.

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

The condition - a build-up of pressure in the eyeball - can damage the optic nerve and lead to blindness if not treated. 

While early diagnosis can prevent further sight deterioration, damage to the optic nerve cannot be undone.

The condition can make the eyes more sensitive to light, resulting in sufferers wearing dark glasses.

Bono's interview and U2's performance air on BBC One at 10:35pm on Friday October 17.

On the controversy surrounding U2's decision to give away their new album Songs of Innocence to 500 million iTunes subscribers as a free gift, Bono says: "We wanted to do something fresh but it seems some people don't believe in Father Christmas.

"All those people who were uninterested in U2 are now mad at U2. As far as we are concerned, it's an improvement."