What does "eyeball to eyeball" mean?

Face to face; especially, about to begin a conflict. For example, We are eyeball to eyeball with the enemy, or In the playoffs we go eyeball to eyeball with the Yankees, or In the first debate our candidate's going eyeball to eyeball with his opponent. This term was originally used only in a military context but later entered civilian language, particularly in political or sports confrontations. [Colloquial; c. 1950]