Eyes have always been described as a way of looking into someone's soul and when you are lying it's often hard to look someone in the face for fear of eye contact giving you away and some of the best examples of characterisation around eyes can be found in John Steinbeck's East of Eden.
Cathy Ames is someone who clearly does not operate to the same rules as you or I and Steinbeck is quick to label her a "monster". In the book Ames is introduced with the story of how she kills her parents. But as the story develops the challenge is to make it obvious to other characters and to the reader that she is dangerous, even when she is not burning people alive, and the way that this is expressed is nearly all through the description of her eyes.
When people meeet her, like Samuel Hamilton, Adam's brother Charles or even the servant Lee, they describe feeling uncomfortable and what they remember most are the eyes - black, cold without a spark of love or kindness.
So many writers use the eyes as a shorthand way of letting the reader know what type of person they are. Some characters seem to always have tears in the corners of theirs or in the other extreme like Cathy they are a window onto a cold soul. I haven't finished East of Eden but for me Cathy Ames is one of the most brutal cold hearted characters that I have so far come across in any book and the reason you know is because of what's in her eyes.