Amaterasu can be avoided by avoiding the eyesight of the caster. That said, Sasuke outrunning Itachi's Amaterasu isn't because of this. There were multiple factors. First of all his eyesight was gradually deteriorating. Secondly the previous defeated Tsukuyomi he attempted left him suffering from it's side effects (intense migraine, worse eyesight). Ontop of that he didn't want to kill Sasuke so he potentially avoided a lethal stare intentionally.
And while I can't prove it, Enton may actually be faster than Amaterasu. When Sasuke missed Raikage with his Amaterasu, the Enton made from it outran Raikage and circled back to prevent him from Karate Chopping him in the neck without sacrificing his arm. I say this because, Enton comes from previously made Amaterasu flames... meaning the literal only way to get the flames to his body in time was if they leapt from the burning samurai's armor, circled around... and fused to Sasuke's riblet Susanoo form.