saccades

Saccades are rapid, ballistic eye movements that reposition the eye so the fovea aligns with a new point of visual interest. They occur during visual exploration, reading, and scanning tasks and are interspersed with fixation maintained by smaller movements such as microsaccades and drifts.

Saccades are characterized by high peak velocities and short durations. Latency after a visual target appears is typically around 100 to 200 milliseconds. The velocity of a saccade increases with its amplitude, following a roughly linear main sequence relationship. During the movement, vision is transiently suppressed, a phenomenon known as saccadic suppression.

Control involves a distributed neural network. Voluntary and reflexive saccades are initiated by cortical areas including the frontal eye fields and supplementary eye fields, with modulatory input from the posterior parietal cortex, and are directed through the superior colliculus to brainstem gaze centers. Horizontal saccades are generated mainly by burst neurons in the pontine paramedian reticular formation, while vertical saccades arise from burst neurons in the rostral interstitial nucleus of the medial longitudinal fasciculus. Omnipause neurons in the brainstem pause their tonic activity to release the burst neurons. The cerebellum, via Purkinje cell inhibition, adjusts saccade amplitude and accuracy (saccade adaptation).

Saccades can be voluntary (pro-saccades), reflexive, or antisaccades, which require suppressing a reflexive glance and looking away from a stimulus. Clinically, saccade assessment helps diagnose and monitor neurological disorders such as brainstem or cerebellar lesions. Ocular motor function is often evaluated with eye-tracking methods including infrared video-oculography or scleral search coils.