Bono has finally revealed why he’s always seen wearing sunglasses. And it’s not rock star stylishness.

In an interview on The Graham Norton Show set to air on the BBC over the weekend, the host asks the U2 singer if he ever takes off his sunglasses indoors. 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 then added, “You’re not going to get this out of your head now and you will be saying ‘Ah, poor old blind Bono’.”

Glaucoma is a build-up of pressure in the eyeball, which can damage the optic nerve and lead to blindness if not treated. It can also make eyes more sensitive to light, a problem aided by wearing tinted lenses.