What are Saccades and What Role Do They Play in Our Life?

Saccadic eye movements are quick, tiny shifts that our eyes make when we look from one point to another. These movements happen so naturally that we hardly notice them. But, believe it or not, they play a crucial role in how we interact with our environment.

According to scientific research, our eyes make approximately 3 saccadic movements per second, which adds up to hundreds of thousands each day!

One of the most common vision deficiencies are oculomotor dysfunctions, which are deficiencies in saccadic eye movements, pursuits, and fixation. Oculomotor deficiencies are normally identified in school aged children because they interfere with academic and sports performance, however they are also often identified after a head injury.

Why Eye Movements Are Critical for Reading and Writing

One of the most common uses of saccadic eye movements is during reading and writing. Our eyes move from word to word and line to line, allowing us to absorb the information. Without these quick movements, reading would be a laborious process. One thing to point out is that when a child needs to work extremely hard to read, this often causes a lack of motivation, which is commonly misinterpreted as a behavioral problem.

What do Problems With Saccades Look Like?

Here is a basic passage that a first-grader should be able to read, along with how they might read it if they have issues with saccadic eye movement.

Example 1

Normal Reading

The dog ran after the ball.

The dog jumped over the fence.

The dog caught the ball and wagged its tail.

Impaired Saccadic Eye Movement Reading

The ran after ball.

The dog over the fence.

The caught ball wagged tail.

Example 2

Normal Reading

The sun was shining brightly.

The kids were playing in the yard.

They all enjoyed a fun game of tag.

Impaired Saccadic Eye Movement Reading

The was shining.

The kids playing yard.

They all a fun of tag.

Driving

When driving, our eyes constantly jump from one focal point to another—checking mirrors, reading road signs, and keeping an eye on the traffic ahead and around us. Saccadic movements help us compile all this information swiftly, making us more effective and safer drivers.

Playing Sports

In sports, especially fast-paced ones like tennis or basketball, your eyes are continually moving to track the ball, players, and other elements in the game. Effective saccadic movements help in improving your reaction time and overall performance.

Watching TV or a Computer Screen

Even while watching television or working at a computer, our eyes are busy making saccadic movements as we scan the screen, read text, or focus on different elements like images or headlines.

Social Interactions

Eye movements are also crucial during conversations. We use them to make eye contact, read facial expressions, and even signal non-verbal cues. Effective eye movements can aid in better communication and more meaningful social interactions.

Navigating Through Spaces

Whether you're walking through a crowded area or maneuvering around obstacles, your eyes guide you through. Quick eye movements help you assess the environment and make real-time decisions to navigate safely.

Identifying Objects and Details

When you're shopping or cooking, you often have to quickly scan your environment to find specific items or read labels. These activities require well-coordinated eye movements.

Job-Specific Tasks

Certain jobs, like those in construction, aviation, or even optometry, require specialized use of saccadic eye movements to focus on various details quickly and accurately.

Symptoms and signs of issues with saccadic eye movements

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Below are some signs that suggest a child might be experiencing issues with saccadic eye movement:

Challenges in copying text from the board or another paper without making errors or leaving out words.
Struggles with reading multiple lines of text, often losing one's place or needing to use a finger or a marker to keep track.
Frequent spelling errors and inconsistent performance in tasks, including fluctuating accuracy and difficulties on timed tests.
Inconsistencies in the quality of writing, such as poor spacing and alignment on lines.
Visual issues while reading, including blurriness, double vision, or words appearing to move on the page.
Reduced attention span, easily distracted, and requiring more time to complete visual tasks compared to peers.
The tendency to move the head instead of just the eyes while reading or needing to adopt unusual postures for comfort.
Challenges in understanding and remembering what has been read, affecting reading comprehension.
Struggles with math and difficulties in coordinating head, body, and eye movements, affecting hand-eye coordination.
A need for tactile or kinesthetic methods to assist in eye-related activities.
Physical discomfort such as headaches, eye strain, or eye rubbing after reading tasks.
Poor coordination affecting sports performance, issues with depth perception, and susceptibility to spatial disorientation or motion sickness.

How Traumatic Brain Injuries Affect Saccadic Eye Movements

Traumatic brain injuries can have a profound impact on various functions of the body, including vision. Saccadic eye movements, which are vital for daily activities like reading and driving, can be significantly affected by brain injuries.

Impact of Concussion

In a study, researchers used a Wii Balance Board and a soccer game to study eye movements in people who had sports-related concussions. They compared these people to athletes who didn't have concussions. They found that the people with concussions had eye movements that were bigger and faster than normal, and they had trouble smoothly following moving objects.

This fits with an older study that also found people with concussions, from various causes, made more mistakes in directing their eye movements. These people had trouble with the accuracy of where they were looking. It's worth noting that the older study included people with more severe symptoms like loss of consciousness, which might have made the results more noticeable.

In short, both studies suggest that concussions affect how accurately and smoothly people can move their eyes.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9682364/

Reduced Speed and Accuracy

One of the most common effects of brain injuries on saccadic eye movements is a reduction in speed and accuracy. Patients may experience delays in initiating eye movements, or their eyes might not land precisely where intended.

Difficulty in Coordination

Brain injuries can disrupt the coordination between both eyes, causing them to move out of sync. This can lead to double vision and make tasks like reading or driving more challenging.

Impaired Reflexive Saccades

The automatic, reflexive saccades may become sluggish or imprecise. This can compromise your ability to quickly focus on unexpected stimuli, which is crucial for activities like driving.

Challenges with Voluntary Saccades

Voluntary control over eye movements can also be compromised. Initiating a voluntary saccade may become difficult, and there may be an increased rate of errors, such as overshooting or undershooting the target.

Impact on Antisaccades

Brain injuries can specifically impair your ability to perform antisaccades, making it difficult to look away from a distracting stimulus. This can be particularly troubling for tasks that require concentration.

Abnormalities in Microsaccades

These minute adjustments in eye position can be affected, leading to visual fatigue and difficulty maintaining a steady gaze.

Increased Frequency of Express Saccades

In some cases, brain injuries might lead to an unusual increase in express saccades, making it challenging to focus on a single point for an extended period.

If you or someone you know has had a TBI, it's essential to consult your eye care professional for a functional eye exam, which can help evaluate the state of your visual system, including saccadic eye movements.

Saccadic Eye Movements and Neuro Developmental Delays

A recent study provides evidence that children with dyslexia, ADHD and Developmental Coordination Disorder were found to have worse outcomes of saccadic eye movement than in the group of children without neurodevelopmental disorders. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8293429/)

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Different Types of Saccadic Eye Movements

Saccadic eye movements might seem straightforward, but they can be broken down into different types, each serving specific functions. Knowing these can help you better understand the complexities of our visual system.

The Difference Between Saccades and Pursuits

Saccades

Quick, short eye movements
Used for shifting gaze
Can be voluntary or involuntary
Visual processing reduced during movement

Pursuits

Smooth, longer-lasting eye movements
Used for tracking moving objects
Generally controlled voluntarily
Visual processing continues during movement

Vertical Saccades

Vertical saccades allow your eyes to move up and down. These are crucial for tasks like reading a book, where your eyes must move from the end of one line to the beginning of the next. Vertical saccades are also important when you're walking, allowing you to look down at the path in front of you and then back up to see where you're going.

Common Uses

Reading and writing
Scanning up and down a computer screen
Navigating stairs
Looking up at signs or down at your phone

Challenges

Impaired vertical saccades can make tasks like reading or navigating stairs difficult and may indicate neurological issues. In some neurological diseases, such as Progressive Supranuclear Palsy (PSP), vertical saccades are more prominently affected than horizontal saccades.

Horizontal Saccades

Horizontal saccades allow your eyes to move side to side. These are crucial when you're reading, as your eyes move across a line of text. They're also essential for tasks like driving, where you need to look from side to side to assess the environment and traffic.

Common Uses

Reading and writing
Driving or cycling
Watching sports or following a moving object
Scanning a crowd or room

Challenges

Problems with horizontal saccades can make it difficult to track moving objects or read text efficiently. Impairments in horizontal saccades are often easier to recognize and can be associated with a variety of neurological or ophthalmic conditions.

Reflexive Saccades

These are automatic and occur in response to a stimulus. If a bright flash or sudden movement happens in your peripheral vision, your eyes will automatically jump to it. This kind of saccade is essential for reacting quickly to potential dangers, like a car suddenly pulling out in front of you.

Antisaccades

In certain situations, you need to look away from a strong visual or auditory cue. This is where antisaccades come into play. For example, if you're trying to focus on work but there's a distracting noise or movement, an antisaccade helps you maintain your focus and not look at the distraction.

Express Saccades

These are extremely quick eye movements, typically executed in less than 100 milliseconds. They're thought to be a result of practice and are common in activities requiring rapid focus shifts, such as video gaming or certain sports.

Microsaccades

These are tiny, almost imperceptible movements that occur even when you try to keep your gaze fixed. They prevent the fading of the visual scene by constantly refreshing the image on your retina.

Sequential Saccades

When your eyes jump between multiple points in a sequence, these are called sequential saccades. For example, when scanning a room, your eyes may jump from one face to another in a particular order.

Medical Conditions That Can Impact Saccadic Eye Movements

Saccadic eye movements can be affected by a variety of medical, eye-related, and neurological conditions. Here's a list of some conditions known to have an impact:

Progressive Supranuclear Palsy: Primarily affects vertical saccades
Traumatic Brain Injury: Can severely affect both speed and accuracy
Stroke: Depending on the affected brain area, can have a significant impact
Cerebellar Ataxia: Directly affects coordination and timing
Optic Neuritis: Can affect saccadic speed and accuracy
Strabismus: Affects coordination of eye movements
Retinal Diseases: Impair the visual input guiding saccades
Myasthenia Gravis: Fatigues the eye muscles, affecting saccades
ADHD
Autism
Childhood-onset schizophrenia

How does a Functional Optometrist Test Saccades?

A functional optometrist tests saccades, or quick eye movements, through various methods to understand how well a person's eyes are working. One commonly used test is the NSUCO oculomotor test, which is a quick and effective way to check the overall functioning of eye movements. In this test, the optometrist assesses four key factors:

Ability: How well the patient can stay on task.
Accuracy: The precision of the eye movements.
Head Movement: Whether the patient has to move their head excessively to follow the target.
Body Movement: How well the patient controls their body while their eyes are moving.

Some other tests that might be used include the Developmental Eye Movement (DEM) test and the King-Devick test. These look at reading speed, visual processing, and other linear visuomotor skills. Specifically, the DEM test can separate issues related to automatic eye movements from other factors, something the King-Devick test can't do.

Watch this video to learn more about the DEM test.

Advanced techniques, like the visagraph or readalyzer, use video-oculography to capture and analyze tiny eye movements. These high-tech tests can also provide an estimate of the patient's reading grade level.

Throughout all these tests, the optometrist will also observe for any compensatory actions like head movements or using a finger to guide reading, as these can indicate potential issues.

How Traumatic Brain Injuries Affect Saccadic Eye Movements

Vision Therapy for Saccades

Vision therapy is the treatment of choice for oculomotor dysfunction. Vision therapy offers various exercises specifically designed to improve saccadic eye movements. Here are some of the exercises and how they can benefit patients:

Targeted Saccadic Training

Individualized exercises help to directly train the eyes for quick, accurate movements.

Pencil Saccades: Patients focus on a word or letter on a pencil while it moves, honing their eye control and coordination.

Spatial Awareness

Strengthening the brain-eye connection for better awareness and positioning.

Hart Charts: Reading numbers or letters off a chart at varying distances and speeds can help in improving the precision of saccadic movements.

Horizontal and Vertical Drills

Training the eyes to move smoothly across both horizontal and vertical planes.

Wall Saccades: Patients focus on multiple targets on a wall, practicing quick shifts in eye focus without turning the head.

Letter Tracking

Enhancing the ability to keep track of symbols or letters during quick eye movements.

Ann Arbor Letter Tracking: This involves reading letters across a page as quickly and accurately as possible to boost saccadic tracking ability.

Adaptive Training

Improving the eyes' ability to adapt to new visual information.

Monocular Prism Jumps: Wearing prismatic lenses, patients practice quick focus changes, which trains the eyes to adapt to new visual scenarios swiftly.

Eye-Hand Coordination

Incorporating other body movements to enhance eye-hand coordination.

Marsden Ball: A suspended ball with letters or patterns is used. Patients track the ball's movement while reading or identifying the patterns, improving both saccades and eye-hand coordination. Learn more about Marsden ball.

Regular evaluations ensure that the therapy is tailored to each individual's progress, making vision therapy an effective approach to improving saccadic eye movements.

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