Saccadic Eye Movements/Saccades
Saccadic eye movements are extremely fast, small,
jerky movements of both eyes in the same direction.
They are used to redirect the line of sight, allowing the
eyes to fix on a still object as the head turns or a
person moves. Saccadic eye movements are common
during reading.  While saccadic eye movements are
normal, they are also present in abnormal conditions of
the eye. The most common examples are pathological
nystagmus and opsoclonus in which fast eye
movements appear to jerk uncontrollably. 
Testing for saccadic eye
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Saccadic eye movements are controlled by two areas of the brain: the frontal eye fields
and the superior colliculus. The frontal eye fields is an area in the front of the brain
(known as the frontal lobe) which helps control visual attention and eye movements.
This makes sense because the areas of the frontal lobe (i.e., the prefrontal cortex and
premotor cortex) where the the frontal eye fields overlap play roles in planning and
initiation of movements. The superior colliculus is an area located deep within the
bottom of the brain that helps control eye movements. It plays a major role in moving the
eyes towards a suddenly appearing noise or motion in the environment and will
automatically trigger saccadic eye movements.

People are generally unaware that their eyes do not remain still when fixating on
something (such as the words on this screen) and are actually moving fast around
various fixation points. The speed of each saccade is uncontrollable.
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Saccadic eye movements are also known as saccades,  although
saccades can also refer to fast movements of other body parts
(such as the head), fast movements of a device, a quick change in
signal frequency, or any other quick change. A form of therapy
known as eye movement desensitization and reprocessing (EMDR)
for anxiety works by causing the patient to have saccadic eye
movements while thinking about an event that produces anxiety,
such as a traumatic memory. Saccades are the quickest
movements the body can produce. The opposite of a saccadic eye
movement is a smooth pursuit, which allows eyes to closely follow a
moving object. 
Saccadic means jerky and comes from the Greek word "saccader" meaning "to jerk," and the Greek word
"ikos" meaning "pertaining to." Put the two words together and you get "pertaining to jerking."