Focus is using your energy – turning on the current, physically and psychologically.

Why Eye Contact?

The eyes, more than any other part of the body, reveal our mental process.  If they wander, we feel the mind is wandering.  If they search, we feel the mind is searching.  And if they focus strongly, we feel the mind is focused strongly.  Find a focus that reflects clearly as possible the way the mind is functioning.
If the focus of the communicator wanders, or is self-conscious, the mind of the audience will do likewise, whether consciously or not.  Wandering, uncertain, or generalized focus is eye-body-mind language that says there is nothing of sufficient interest to think about.
When the focus of concentration shifts in a presentation, the individual must signal the shift – using vocal tone, vocal duration, pitch along with a verbal transition signals the shift.

The use of focus provides the signs of concentration.  The use of effective eye contact signals the right focus.  It also points to your right level of intention.