The U2 frontman says he's suffered from the eye condition for 20 years
The band think giving away the album for free "was a great thing to do"
Group also release video for 'The Miracle (Of Joey Ramone)'
Band have previously been accused of tax evasion
Album is downloaded 26 million times as band talk-up 'Songs Of Experience' follow-up
The Irish band will be joined by Interpol, Zola Jesus and Sam Smith on the BBC Two programme
The OneRepublic man assisted with 'Songs Of Innocence'
'Songs Of Experience' will follow the recently released 'Songs of Innocence'
The band's last major tour was the ambitious U2 360° Tour of 2009 to 2011
Drummer Larry Mullen Jr. embraces his son in black and white shot