Eye Contact is important because insufficient or excessive eye contact may create communication barriers. It is important in relationship because it serves to show intimacy, attention, and influence. As with facial expressions, there are no specific rules governing eye behavior except it is considered rude to stare, especially at strangers. It's, however,common for two strangers to walk toward each other, make eye contact and say "Hi".
The strangers may immediately look away and forget that they even had any contact. This type of glace does not mean much ; it is simply away of acknowledging another person's presence. In a conversation too little eye contact may be seen negatively because it conveys lack of interests, inattention, or even mistrust. The relationship between mistrust and lack of eye contact is stated directly in the expression, "Never trust a person who can't look you in the eyes".
Posted on presentation of CCU subject.
Source : Levine, D.R., Beyond Language, p. 46