'Ah, poor old blind Bono' - U2 singer reveals 20-year fight with glaucoma
Considered by many to be no more than a rock star affectation, the dark shades are actually protection for his eyes.
Bono explained during a recording of The Graham Norton Show he has suffered from glaucoma - a condition which causes a build-up of pressure in the eyeball that can damage the optic nerve and lead to blindness if not treated - for the past 20 years.
Presenter Norton, originally from Bandon in west Cork, asked why Bono was never seen without his sunglasses.
Bono replied: "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 added: "You're not going to get this out of your head now and you will be saying 'Ah, poor old blind Bono'."
Glaucoma can make eyes highly sensitive to light, with some glaucoma medications exacerbating the problem. Sunglasses make life more comfortable for glaucoma sufferers and also protect the eyes from the further damage of UV rays.
U2 were appearing on the show to promote their new album, Songs Of Innocence, which was released commercially this week after being given away to half a billion iTunes customers who had the songs automatically downloaded.
The move sparked controversy with many iPhone owners subsequently deleting the free album.
However, Bono said those unhappy with the offer didn't believe in the spirit of Christmas generosity. Speaking about the furore, Bono told Norton: "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," he joked.
Speaking following his interview with the band, Norton said he felt privileged to have the Irish rock quartet on his couch and described their performance as "special".
"I had a ball," said the presenter. "U2 were in and they did a stripped-back acoustic thing sitting on the couch with the guitars.
"You are sitting two feet away from Bono giving it all. It is amazing - a real privilege."
He added: "The U2 thing was really just special. It was one of those great nights in the studio. The audience was just buzzing at the end of it."