A saccade is a rapid, jerky movement of the eye that shifts your gaze from one point to another. You make thousands of them every day, whether you’re reading this sentence, scanning a room, or glancing at your phone. They are the fastest movements the human body produces, with the eye reaching peak velocities close to 400 degrees per second for large shifts and exceeding 500 degrees per second in brief bursts. The word comes from the French term for flicking the reins of a horse.
How Saccades Work
Your eyes can’t process visual detail across a wide area at once. Only the fovea, a tiny region at the center of your retina, sees in high resolution. Saccades solve this problem by rapidly redirecting your line of sight so the fovea lands on whatever you want to examine next. Between saccades, your eyes hold relatively still during periods called fixations, which is when your brain actually takes in visual information.
Six small muscles attached to each eyeball carry out the movement, controlled by three cranial nerves. For horizontal saccades (looking left or right), the key players are the lateral rectus muscle, which pulls the eye outward, and the medial rectus muscle, which pulls it inward. Vertical saccades involve a more complex set of muscles including the superior and inferior rectus and the oblique muscles. A brainstem circuit coordinates these muscles so both eyes move together in the same direction at the same time.
Why You Don’t See a Blur
During a saccade, the image on your retina smears across the visual field at high speed. You should, in theory, see a streak of motion blur every time your eyes jump. You don’t, because your brain actively suppresses visual processing during the movement through a mechanism called saccadic suppression.
This works through a kind of internal memo system. When the brain sends a command to move the eyes, it also sends a copy of that command, called a corollary discharge, to visual processing areas. That copy acts as a warning signal, temporarily dampening the response to incoming visual information. Research published in the Journal of Neurophysiology traced this circuit from the deeper layers of the superior colliculus (a midbrain structure involved in eye movement) through inhibitory neurons that suppress activity in visual areas. The result is a seamless visual experience: your brain essentially edits out the blur and stitches together the stable images from before and after each saccade.
Types of Saccades
Not all saccades are the same. They fall into a few functional categories depending on what triggers them and how much cognitive effort they require.
- Reflexive saccades are automatic responses to something appearing in your peripheral vision. A flash of light, a sudden movement, or a new object triggers a quick, largely involuntary shift of gaze. These require the simplest processing and have the shortest reaction times.
- Voluntary saccades are deliberate, goal-directed eye movements. When you decide to look at a specific word on a page or check your side mirror while driving, that’s a voluntary saccade. These take slightly longer to initiate because they involve higher-level decision-making.
- Antisaccades require you to look in the opposite direction of a visual cue. If a light appears on your left, you must suppress the natural urge to look at it and instead look right. These are cognitively demanding because they require inhibiting a reflexive response, and error rates on antisaccade tasks are used to measure executive function.
There are also microsaccades, which are tiny involuntary eye movements that happen even when you think you’re holding your gaze perfectly still. These were first described in the 1930s and typically measure less than one degree in amplitude (most fall in the range of 0.03 to 0.41 degrees). They occur roughly once per second during fixation and appear to help maintain vision by preventing the retinal image from fading, which happens when a stimulus stays perfectly motionless on the retina for too long.
The Brain Regions Behind Saccades
Two brain areas share the primary responsibility for generating saccades. The frontal eye fields, located in the frontal cortex, handle the voluntary side of things: selecting a target and deciding when to initiate the movement. This is the region most involved when you choose where to look next. The superior colliculus, a structure in the midbrain, sits closer to the motor side and plays a major role in reflexive target selection and preparing the movement for execution. Both regions also contribute to visual attention, meaning the same circuits that move your eyes help you focus your attention even before your eyes start moving.
The parietal cortex rounds out this network, integrating spatial information about where things are in your visual field. Together, these three areas form a coordinated system that handles everything from a reflexive glance at a loud noise to the deliberate scanning pattern you use while reading.
How Saccades Change With Age
Saccadic performance follows a clear arc across the lifespan. A study in Investigative Ophthalmology & Visual Science tracked horizontal saccades from early childhood through old age and found striking differences. At age 3, the average reaction time before initiating a saccade was 439 milliseconds. That dropped steadily to 172 milliseconds by age 14, reflecting the maturation of the brain circuits controlling eye movements. Reaction times then stayed relatively stable through age 50 before gradually climbing back up to 264 milliseconds by the 80s and beyond.
Accuracy changes too. Saccades tend to slightly undershoot their target throughout life, falling about 10% short on average. But after age 50, this undershoot becomes more pronounced for larger eye movements. By the ninth decade, saccades aimed at targets more than 20 degrees away were undershooting by nearly 40%. Younger people under 20 showed a different pattern: they tended to slightly overshoot small targets and undershoot large ones.
Saccades as a Window Into Brain Health
Because saccades depend on so many brain systems working together, they can reveal problems long before other symptoms become obvious. This makes them valuable in diagnosing and tracking several neurological conditions.
In Parkinson’s disease, patients show a distinctive pattern of saccadic problems. Their saccades are hypometric, meaning the eyes consistently fall short of the target and need extra corrective movements to reach it. Their reaction times are also slower, averaging around 200 milliseconds compared to 140 milliseconds in healthy adults. This delay correlates strongly with disease severity and may serve as a non-invasive way to track how the disease progresses over time. Antisaccade tasks are particularly revealing: Parkinson’s patients make significantly more errors, reflecting the damage to frontal-striatal circuits that control impulse inhibition. These specific saccadic signatures also help doctors distinguish Parkinson’s from other conditions like progressive supranuclear palsy and multiple system atrophy, which produce their own distinct eye movement patterns.
In concussion assessment, saccades have become part of standardized screening tools. The Vestibular/Ocular Motor Screening (VOMS) tool tests horizontal and vertical saccades alongside other eye movements. A patient is asked to rapidly shift their gaze between two points held at shoulder width for horizontal testing or between forehead and chest height for vertical testing. Research on pediatric concussions found that horizontal saccade testing could distinguish concussed patients from healthy controls, with horizontal gaze stability showing particularly strong diagnostic performance.
How Saccades Are Measured
Modern eye tracking uses infrared cameras pointed at the eye, capturing its position many times per second. The camera detects reflections from the cornea and pupil to calculate exactly where the eye is pointing at any given moment, then computes velocity, acceleration, and accuracy from those position measurements. Systems running at 100 frames per second are common in clinical and research settings, though some research has shown that even cameras sampling at 50 frames per second can capture peak saccade velocity with reasonable accuracy. Higher sampling rates give more precise measurements, which matters when you’re trying to detect subtle abnormalities in patients with early-stage neurological disease.