Saccades are eye movements that quickly shift the eye’s focus between two fixed points. They are used any time that your gaze moves from one point of gaze fixation to another. For example, if you are reading a book when you move from word to word or transition from the end of a line to the start of the next one.
In an ideal scenario, saccades are quick and accurate movements. Healthy brains and eyes can normally saccade to a new target in 1/10th of a second or less. However, brain injuries and damaged neural pathways can lead to irregular saccadic eye movements (which we discussed in a past blog).
Watch the fourth video in our Introduction to PCS Management series to find out more about saccades and how they are related to brain injuries:
In this blog, we will talk about two different types of saccades, the importance of saccades to everyday activity, and the impact of brain injuries on saccades. Please leave a comment below if you have any questions.
Types of Saccades
There are a number of different types of saccades, but our discussion will focus on the two highlighted below:
- Volitional Saccades
- Predictive Saccades
- Memory-Guided Saccades
- On Command Saccades
- Reflexive Saccades
- Express Saccades
- Spontaneous Saccades
- Quick Phases of Nystagmus
A reflexive saccade occurs when your eyes look at something new that appears in your field of vision, or when you hear something that causes you to react. These saccades are largely unconscious, driven by functions lower down in the brainstem.
Reflexive saccades can be overridden or inhibited by higher cortical areas of the brain. In practical terms, this means that the brain can choose to ignore things that it knows are unimportant. This ability is an important part of healthy brain function, which we discussed in more depth in this blog on post-concussion syndrome depression and anxiety.
Volitional saccades occur when we are reading words on a page, scanning an area looking for something, or taking in our environments. These saccades are under our conscious control, driven from the frontal lobes of the brain. Volitional saccades can be used to retrain impaired brain function, but only under very specific conditions.
The Importance of Saccades
Unconscious Collicular Map
Our brain uses saccadic eye movements to create a constantly updated, unconscious map of our body in relation to its environment. Visual stimuli from our eyes will produce neural activity in a part of our brain called the superior collicus, which is why this unconscious map is called the ‘collicular map’.
This unconscious map allows us to reach for objects outside our field of vision, avoid obstacles and balance as we move. However, if our brain is injured, then this map will be wrong — causing us to become clumsy, bump into things, or get lost when reading.
Impact of Brain Injuries
Brain injuries can have a number of effects on the quality of both reflexive and volitional saccades. The good news is that your saccades can also help us diagnose the site of the injury.
At Northoak Chiropractic, we can measure the speed and accuracy of saccades. Frontal lobe injuries can lead to slow or late saccades. Cerebellar injuries can cause inaccurate saccades, that fall short or go past their targets. If saccades are bad in one direction and good in another, this can also help us identify what brain areas are injured.
The way to free yourself from these problems is to carefully drive neuroplasticity in the injured brain pathways, where function has been lost. This is done indirectly at first, then directly as function improves. Depending on the injury, pursuits and reflexive saccades can be used to improve plasticity — but it is very important to correctly diagnose the injury first.
If you have experienced a past brain injury and want help recovering, please give us a call at (905) 338-5951 or contact Dr. Jay at Northoak Chiropractic.