I did these studies of eyes back in college when trying to improve my understanding of human anatomy. It's interesting, isn't it, the degree to which you can read the emotion of each face in the eyes alone.
These are the emotions I see in them: Top left: I'm intrigued and interested in what your saying. Please keep going. Top right: I sympathize with you. I'm really sorry for you. Bottom left: You really believe that? Are you crazy? Bottom right: You are the vilest creature I've ever encountered.
No wonder they say "Eyes are the windows of our soul". As far as i understand everything is within the muscles, wrincles and such which make the eyes of a person unique. But i'm still a beginner, trying to find a way to understand how to draw eyes better.