Version eye movements: the eyes make a rotation of the same amplitude and in the same direction.
These movements are needed when the object of interest moves in front of the observed without changing its distance from him.
Vergence eye movements: the eyes make a rotation equal in amplitude but with opposite direction. These movements are needed when the object of interests move in depth with respect to the observer.
Saccadic eye movements (saccades)
Saccades are the fastest eye movement produced by the oculomotor control system that enable to rapidly redirect the line of sight.
They include both voluntary and involuntary changes of fixation, the quick phase of vestibular and optokinetic nystagmus, and the rapid eye movements that occurr during REM sleep.
Saccades show a unique feature: an invariant relationship between their peak velocity and the size of the movement. The bigger the eye movement, the greater its top speed.
A typical saccadic eye movement accelerates rapidly, reacking its peak velocity. The eye then decelerates and usually stops relatively abruptly.