Another form of oculomotor dysfunction (for a review of oculomotor dysfunction check out our article: Understanding Oculomotor Dysfunction and Exercises to Treat) stems from an issue with saccades—or saccadic dysfunction.
What is Saccadic Dysfunction?
Saccades are eye movements in the same direction used to look left and right, to switch focus quickly from one thing to another, and track objects such as when reading or writing.
If saccadic eye movements are not properly tuned, it can lead to overshooting or undershooting of the eye movements, resulting in looking too far in one direction or not far enough. When the eyes overshoot or undershoot a correctional mini-saccade is induced to correct the error in movement and bring the object of focus into correct view.
While these errors may not cause too many problems when they occur infrequently, constant saccadic dysfunction can lead to many problems including difficulty reading, eye strain/fatigue, the appearance of words or letters “swimming” around on the page, headaches, and sometimes even misdiagnosis of dyslexia.
Think about it like this—let’s say a child with saccadic dysfunction is trying to learn how to read. The child is shown the word “dog”.
When the child tries to make small saccades to read the word letter by letter, his eyes overshoot, causing him to see the letter “g” first. The correctional mini saccade then shifts over to see the “d”.
Instead of interpreting this word as “d-o-g” this child sees it as “g-o-d”, a completely different word with a completely different meaning.
Or perhaps this individual is able to read individual words correctly, but due to saccadic dysfunction sentences shift around.
Instead of being able to read the sentence “the dog jumped over the fence and ran down the street”, the individual may read “dog over the jumped fence down the street ran”.
The second sentence, of course, makes no sense. In order to combat this jumbling of words, the individual may read excessively slow, need to use a finger to help guide themselves along the sentence, or even just avoid reading all together.
Individuals with saccadic dysfunction may have a difficult time explaining their symptoms, as this is a problem that is commonly seen post brain-injury (i.e. concussion) or congenitally (from birth, where the individual does not realize the problem is abnormal). Thus, this problem may go undiagnosed for many years unless a thorough eye exam is performed.
Testing for Saccadic Dysfunction
During the initial eye exam, the doctor will perform a variety of tests to help tease out the problem to see if it is truly a problem with saccades, or a visual information processing deficit.
Some of the most common tests for saccades are the NSUCO oculomotor test, Developmental Eye Movement (DEM) test, and the King-Devick Test.
The NSUCO oculomotor test is used to test both horizontal saccades and a separate ocular movement called pursuits.
To test saccades, the patient is asked to stand up. The examiner stands roughly 40 centimeters in front of the patient holding two targets (most frequently a small back steel wand and a small gold steel wand) that are held 20 centimeters apart. The patient is then asked to switch focus back and forth between the two targets and the examiner watches the eyes’ movements for accuracy.
The Developmental Eye Movement test (DEM) is a written exam that can be used to differentiate between a problem with saccades or visual information processing speed.
An individual is asked to read a column of vertically stacked letters as quickly as possible. The same is then repeated with horizontally stacked letters.
The examiner keeps track of any errors or letters skipped and records the errors and time to create a ratio score which is then compared to age-matched norms.
While we won’t get into the specifics of the ratio here, here is a basic understanding of the results:
A normal vertical response but an abnormal horizontal response indicates saccadic dysfunction.
An abnormal vertical response but a normal horizontal response indicates poor test reliability.
An abnormal vertical and abnormal horizontal response can indicate either a problem with random automaticity of naming (given the ratio is within normal limits) or a problem with both random automaticity of naming and saccadic dysfunction (given the ratio is outside of normal limits).
The King-Devick test is a verbal test in which an individual is show letters displayed horizontally on a card. He/she is asked to read off the letters as quickly as possible.
The examiner watches the patient’s eye movements and checks the accuracy of the patient’s ability to read off the letters on the card to determine if saccadic dysfunction is present.
How Can We Treat Saccadic Dysfunction?
Saccadic dysfunction is treated with vision therapy to try and lessen symptoms to improve reading time and comprehension. Vision therapy will aim on the patient moving his/her eyes to look at various objects while holding his/her head still.
There are many types of vision therapy exercises that can be performed to help improve saccadic accuracy including Hart Chart Saccades, Saccade Sticks, worksheets such as the Visual Tracking Worksheet series or Letter/Word Tracking Worksheet series, computer programs such as the VTS system, and even incorporation of popular childhood games (with modification of course).
Hart Chart Saccades involves a chart with random letters or numbers. The patient is asked to read a letter from the left side of the chart and then skip to read a letter on the right side of the chart.
This process is repeated several times to work on fine tuning the accuracy of the saccadic system.
To make the task more difficult, the individual may be asked to read letters that are more close together on the chart (i.e. the two letters located in the center of the chart). This is because fine movements are more difficult for the muscle system to complete accurately.
Saccade sticks work similarly to Hart Chart Saccades, but involve two large sticks with letters and pictures on them. The patient is asked to name the letter or picture on the left stick, and then shift his or her eyes over to the right stick to read the corresponding letter or picture.
Saccade sticks can be helpful because the distance between the objects (i.e. the size of the saccades) can be altered by moving the sticks closer together or further apart.
Worksheets can be used to improve saccadic dysfunction and are helpful for creating a “real world” situation to improve reading accuracy and speed.
Worksheets are specially designed to work the saccadic system. These are great for home therapy and illustrate improvement based on an increase in speed and accuracy of saccades over time.
The VTS system is a computer program loaded with various exercises for different oculomotor dysfunctions. It requires specialized computers and technology and is therefore usually reserved for in-office therapy sessions.
Depending on the patient’s age, the vision therapist or doctor can incorporate games the child likes to play to make vision therapy less intimidating and more fun.
The therapist will choose games in which the child is asked to search or compare images such as Spot It, Matching, Hidden Object Diagrams, etc. The therapist will remind the patient not to move his/her head and to only use his/her eyes to play the game.
Therapy activities are always customizable and will be dependent upon the patient and his/her abilities. The doctor will work with the patient to create a treatment plan best suited for his/her needs and goals, and can be adjusted at any time.