Eye movements are unique in that each eye movement has a different pathway through the brain. The eyes are like a puppet, and the brain like the puppeteer. The eyes only do what the brain tells them to do. As providers, this is our window to see how various aspects of the nervous system are functioning. We can use these eye movements to narrow down which areas are impacted, and then we can use the eye movements therapeutically to exercise parts of the nervous system.Â
Types of Eye Movements
Gaze: This is your ability to hold your eyes steady on a target. An example of this would be looking at a stop sign.
Pursuits: This is your ability to follow a single moving target. An example of this would be watching a plane fly by.
Saccades: These are quick eye movements in which you look from one target to another. An example of this would be shifting your focus from a quarterback to the receiver.
Optokinetic Nystagmus: This is a reflexive eye movement, in which your eyes perform a pursuit and then a saccade. This is elicited by tracking a moving field. An example would be if you were driving a car and saw the world move by.
Convergence: This is your eyes ability to move together inward to focus on a close target. An example of this would be if you were to look at your phone within arm's length.
Divergence: This is your eyes ability to move together outward to focus on a far away target. An example of this would be looking at a distant object like a television.
What are some examples of visual disturbances?
The majority of dysautonomia patients have dysfunction in their brainstem, which is the main control center for the autonomic nervous system. Consequently, there are a multitude of visual symptoms that patients may experience.
Dry Eyes: This can be from lack of blood flow to the eyes, instability of the eyes to fixate resulting in your eyes feeling tired, or lack of parasympathetic output to the lacrimal glands which keep the eyes moist.
Light Sensitivity: This is a big issue for many dysautonomia patients. The main function of the brain is to inhibit our surroundings so that we are only taking in a limited amount of information. When the brain is not functioning as well, it lets in excess information, including light. The top part of the brainstem, called the midbrain, receives visual information from the retina and sends the information to various regions of the brain to be processed. This lack of inhibition can lead to visual symptoms like light sensitivity, visual ripples, glares, sunburst appearance around lights, and more.
Blurry Vision: It is not uncommon for dysautonomia patients to suddenly need reading glasses because their vision is blurry. The brainstem is responsible for keeping your eyes steady on a target, called gaze stabilization. When your eyes are not able to fixate on a target (gaze stabilization), there are often square wave jerks to blame. Square wave jerks are quick eye movements (saccades) which are brought out with gaze stabilization. This is often due to dysfunction of the omnipause neurons, which are nuclei responsible for inhibiting burst neurons that cause the eyes to move in the first place. Omnipause neurons are found in the middle region of the brainstem. If there is dysfunction in the brainstem and the eyes are not able to maintain gaze, then the world may appear blurry due to excess eye movements. This is one of the reasons that some patients have 20/20 vision but still have blurry vision or trouble reading.
Visual Snow: With dysfunction in the autonomic nervous system, blood flow is also affected, causing inadequate blood flow to structures responsible for vision such as the eyes and occipital lobes. This can lead to patients experiencing visual snow, due to the inadequate blood supply to the eyes and the occipital lobes which process visual information.
Worsening Vision: More than 50% of the brain is dedicated to visual processing. The brain and brainstem not only control eye movements, but also regulate the autonomic nervous system. There is a lot of overlap of function, which is why dysautonomia patients often have complaints of visual changes. Another reason may be due to the body’s inability to properly shunt blood to the eyes themselves. The constriction and dilation of all blood vessels are controlled by the sympathetic nervous system. When there is inappropriate output of the autonomic nervous system then nutrients, oxygen, hormones, and neurotransmitters are not able to reach the tissues and organs in need. This includes the eyes.Â
Changes in Color Saturation: With dysautonomia, there is a change in efficiency of blood flow and the body’s ability to send blood to the brain. There are four main arteries that supply the brain, the carotids which are in the front of the neck, and the vertebral arteries which are in the back of the neck. The vertebral arteries have branches that supply the occipital lobes, which are in the back of the brain and responsible for processing color. The carotids branch off into numerous divisions, but the very first branch that comes off is called the ophthalmic artery. This supplies the majority of the eye. Your eyes contain cones, which are responsible for color vision. So when this area is not getting adequate blood supply, neither are the cones.
Dizziness with Certain Eye Movements: It is not uncommon for patients to report feeling dizzy when moving the eyes quickly, looking back and forth between objects, or making eye contact. In order to feel stable in our environment, we need visual input, proprioceptive input, and vestibular input. When one or more of these systems are dysfunctional, it causes us to feel dizzy or off balance. Moving your eyes requires a multitude of areas to work together in the nervous system. Most notably, we require our eyes to be stable so that when we move our eyes to a target, we are able to focus on the object. The stability of our eyes on an object largely requires the middle portion of the brainstem, called the pons. With instability throughout the movement and instability at the end of the movement, then we feel dizzy.Â
CFNC'S Approach
At CFNC, we evaluate our patients as a whole. This means that not only are we looking at the function of the oculomotor system, but we are also evaluating the autonomic nervous system, cortex, neural timing mechanisms, balance, and more. We focus heavily on the eyes, because eye movements use many different areas of the brain. This is our best way to get information on the functioning of the whole nervous system. We use a bedside examination for a gross overview of function, as well as diagnostic tests like a videonystagmography and computerized assessment of postural systems to examine the patient under a microscope.Â
Treatment varies from person to person, but it may include eye movement therapy. We can use the eye movements to exercise parts of the brain that are dysfunctional and resulting in symptoms. If you or a loved one have any questions, reach out to one of our clinics to schedule a consultation and discuss your individual case!