Saccades are rapid, ballistic movements of the eyes that abruptly change the point of fixation. Pursuit movements are much slower tracking movements of the eyes designed to keep a moving stimulus on the fovea. Such movements are under voluntary control in the sense that the observer can choose whether or not to track a moving stimulus
The vestibular system has a profound influence on eye movements. You can prove this to yourself by asking a friend to sit in a chair that can be rotated. Before you spin the chair, ask your friend to look at some object opposite them, perhaps a picture on the wall. Note that your friend’s eye will be relatively steady. Now spin your friend for 30 seconds or so and when you stop the chair tell them to try and fixate the same target again. You will note that your friend’s eyes will not be steady; rather they will be moving back and forth. This movement is called nystagmus. Obviously this is an extreme condition. Yet, there is a constant interaction between the vestibular system and the visual system. It is frequently referred to as the vestibulo-ocular reflex (VOR). This reflex is used to stabilize an image on the surface of the retina during head movement.