The human visual system interprets depth in sensed images using both physiological and psychological cues.
All psychological cues are monocular.
In the real world the human visual system automatically uses all available depth cues to determine distances between objects. To have all these depth cues available in a VR system some kind of a stereo display is required to take advantage of the binocular depth cues. Monocular depth cues can be used also without stereo display. The physiological depth cues are accommodation, convergence, binocular parallax, and monocular movement parallax. Convergence and binocular parallax are the only binocular depth cues, all others are monocular.