When the eye rotates in its orbit, there is a point within the eyeball that is more or less fixed relative to the orbit. This is the centre of rotation of the eye. In reality, the centre of rotation is constantly shifting but by a small amount. It is considered, for convenience, that the centre of rotation of an emmetropic eye lies on the line of sight of the eye 13.5 mm behind the anterior pole of the cornea when the eye is in the
straight ahead position (
straightforward position), that is when the line of sight is perpendicular to both the base line and the frontal plane.
See anteroposterior axis;
line of sight.