There are four types of eye movements: saccades, smooth pursuit movements, optokinetic movements, and vestibulo-ocular movements. Saccades are rapid, ballistic movements that change the point of fixation and occur reflexively when focusing on an object of interest. They have characteristics like amplitude, gain, duration, velocity and peak velocity. Saccades can be voluntary or reflexive. Smooth pursuit movements are slower tracking movements to keep a moving stimulus on the fovea and require a moving visual signal to initiate.

1. Types of Eye Movements
• There are four additional types of eye movements: saccades,
smooth pursuit movements, optokinetic movements, and
vestibulo-ocular movements.
1. SACCADE
• Saccades are rapid, ballistic movements of the eyes that abruptly
change the point of fixation.
• Saccades are said to be ballistic because the movements are
predetermined at initiation, and the saccade generating system
cannot respond to subsequent changes in the position of the
target after saccade initiation.
• Saccades can be elicited voluntarily, but occur reflexively
whenever the eyes tries to focus object of interest on the retina.
• The rapid eye movements that occur during an important phase of
sleep are also saccades.

2. Cont….
• A saccade is a rapid, conjugate, eye movement that shifts the
center of gaze from one part of the visual field to another. The
initiation of a saccade takes about 200 milliseconds.
• They may be horizontal, vertical, or oblique.
Terms used to characterize saccades
 Amplitude: The size of the saccade, usually measured in degrees
or minutes of arc. A higher amplitude means the eye has traveled
a greater distance during the saccade.
 Gain: The ratio of the actual saccade amplitude divided by the
desired saccade amplitude. Gains of <1 indicate the saccade was
too small or hypometric and gains of >1 indicate the saccade was
too large or hypermetric.
 Duration: The time taken to complete the saccade. Most saccades
are complete within a few tens of milliseconds.

3. Cont….
 Velocity: The amplitude of the saccade divided by the duration
(commonly reported in degrees per second).
 Peak velocity: The highest velocity reached during the saccade.
 Latency: The time taken from the appearance of a target to the
beginning of a saccade in response to that target.
Classifications
1. Voluntary, endogenous saccades are self-directed eye
movements that can be generated in response to command;
they may require a complex volitional process with intricate
cortical processing.
2. Reflexive saccades, unlike the complex volitional saccades, are
movements of the eyes towards a visual or auditory stimulus.

4. Cont….
SMOOTH PURSUIT OF EYE MOVEMENT
• Smooth 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
• Most people are unable to initiate pursuit without a moving
visual signals.
• Smooth pursuit is asymmetric and most human tend to be
better at horizontal than vertical smooth pursuit.