Cliché as it is, the eyes are indeed the windows of the soul. The eye body language is one of the most powerful mediums of nonverbal communication. It can either support or betray whatever you are saying. Even the slightest movement of the eye can indicate the biggest meaning.
During a conversation, it is normal to have eye contact. It means differently in specific situations. Looking at a person directly to the eye means that you are interested in what he is saying. But the inability to take the eyes of another person when he or she is talking may also indicate doubt, suspicion, or lack of trust.
Appropriate use of eye contact also includes when to break eye contact. A long eye contact has many interpretations. It may mean a focused attention or sign of attraction. But this can sometimes be uncomfortable, thus the trick is to just look at the bridge of the nose. Long eye contact may also indicate a sign of authority or domination if one can do it without much blinking. However, prolonged eye contact may also pose as a threat, so breaking it from now and then is essential. But breaking it may indicate other meanings as well, such as situations wherein one wants to end the conversation, has been insulted or found out, or is being threatened.
The eyes looking at different directions also have different meanings. When one looks up to the right, it means that he is imagining visual images. Meanwhile, when he looks up to the left direction, it means that he is trying to recall a memory. However, there are still instances where it is in a reversed order, depending on the person. Try to test him first by asking him to recall a known memory and to picture out an event.