User blog comment:Umbrello/Please Stop With the Eyes Dripping Blood/@comment-4849011-20140911012920/@comment-4849011-20140911133347

Exactly. When Itachi (and later Sasuke) used mangekyo sharingan (an advanced form of sharingan) to perform the Amaterasu jutsu (a techique which shoots black fire), their eyes bled from the strain.

http://naruto.wikia.com/wiki/Amaterasu

Wait...asking me that was just a trick to lure me back into the open, wasn't it?! ~feels man-catcher around neck~ OH, NO!