I don't know. But sitting here at the desk I can hold a pencil at arm's length and focus on the eraser "aiming" at the doorknob across the hall. I see two doorknobs and they both look about the same. The eraser is under the one on the right.
Sport45 : Your focus is on the pencil rather than the doorknob. Try playing with your focus until you see 2 pencils and one doorknob. One pencil will be more distinct than the other.
Right eye dominant: the left pencil will be most distinct, and aimed at the dorknob.