Steven Sotloff was the second American killed by ISIS - after he was kidnapped by the extremist group in 2013. Lesley Stahl talks to his family - who are still mourning his loss. Two doctors are on a mission to fight blindness -- and partial blindness -- in the isolated country of Burma. Bill Whitaker has their story. When it comes to art -- sometimes you have to be political. Holly Williams meets Chinese artist Ai Weiwei - who has not received the most positive responses to his work.