While wearing the headset, the eyes are accommodated as if the object is far away. Accommodation here is defined as changing the optical power, which is achieved by bending of the lens in our eye by eye muscles. [Aside from Psych 30: Intro to Perception: When the lens is relatively flat and the muscles relaxed, we can see far away. When the lens is bent by contracting muscles, we can focus close up.] Anyways, in a headset, our eyes are focused far away. However, our eyes are also rotated inwards a bit (this is vergence) in order to fuse the two slightly offset images shown to each eye. Normally though, when focusing far away, our eyes don't rotate inward as much. Thus, the headset demands our visual system to behave in a contradictory way -- which leads to symptoms like nausea and fatigue!

Professor mentioned distance 2.2 meters. What is the significance of this?