"Hang On" is a song by the band Weezer. The song impacted radio on February 15, 2011. It is the seventh track and second single from their eighth studio album, "Hurley". The album version of "Hang On" is co-written by Rick Nowels and features Canadian actor Michael Cera on backing vocals and pseudo-mandolin. The single version features no mandolin, and contains a harder sound.
Weezer's front man does not need glasses/contacts to correct his vision.
The lead singer of Weezer famously wears corrective lenses. This does require information outside the text, but it's a relatively well known cultural fact.