Eye movements are unique in that each eye movement has a different pathway through the brain. The eyes are like puppets, and the brain like the puppeteer. In other words, someone’s eyes only do what their brain tells them to do. As providers, this is our window through which we can see how various aspects of the nervous system are functioning. Simply put, the eyes are the windows to the nervous system. We can use eye movements both diagnostically (to determine which areas of the brain are impacted) and therapeutically (to exercise parts of the nervous system).
Types of Eye Movements
Type | Definition | Example |
Gaze | Your ability to steadily keep your eyes on a sedentary (non-moving) target. | Looking at a stop sign. |
Pursuits | Your ability to follow a single moving target. | Watching a plane fly by. |
Saccades | Quick eye movements in which you look from one target to another. | Quickly shifting your focus from the receiver to the quarterback during a football game. |
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. | Seeing the world move by through a window of a moving car. |
Convergence | Your eyes' ability to synchronously move inward to focus on a close target. | Looking at your phone within arm’s length. |
Divergence | Your eyes' ability to synchronously move outward to focus on a far away target. | Looking at a distant object like a television. |
Visual Disturbances
The majority of dysautonomia patients have dysfunction in the 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 reduced blood flow to the eyes (which can affect their ability to stay moist), difficulty for the eyes to maintain stable focus (which can make your eyes feel tired and contribute to dryness), or lack of parasympathetic output to the lacrimal glands which produce tears and keep the eyes moist.
Light Sensitivity: This is a big issue for many dysautonomia patients. The main function of the brain is to filter our surroundings so that we are only taking in a limited/selective amount of information at a time. When the brain is not functioning as well, its “filter” weakens, causing it to let in excess information, including light. The top part of the brainstem, called the midbrain, receives visual information from the retina (a light-sensitive layer of tissue in the back of the eye that's responsible for visual processing) and sends the information to various regions of the brain to be processed. This lack of filtration of sensory information intake can lead to visual symptoms like light sensitivity, visual ripples, glares, sunburst appearance around lights, and more. Light sensitivity is also known as photophobia.
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; this is called gaze stabilization. When your eyes are not able to fixate on a target (not able to engage in gaze stabilization), they might make quick, involuntary movements known as square wave jerks. Square wave jerks occur due to dysfunction in neurons in the middle region of the brainstem called omnipause neurons. Omnipause neurons are normally supposed to control the burst neurons that cause the eyes to make rapid movements in the first place. When omnipause neurons don’t work properly, they fail to inhibit (suppress the activity of) these burst neurons, leading to excessive eye movements. 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 when checked by an eye doctor but still have blurry vision or trouble reading.
Visual Snow: Dysfunction in the autonomic nervous system can affect blood flow, leading to inadequate circulation to structures responsible for vision and processing visual information, such as the eyes and the occipital lobes. This reduced blood flow can impact visual function and overall vision quality. Visual snow is one example of such an impact. This can also be from a common area of dysfunction for POTS patients, called the midbrain. The midbrain is the top part of our brainstem, and has many important functions including regulating the sympathetic nervous system. The midbrain has four small projections - two of them are called the superior colliculi. The primary role of the superior colliculi is to receive information from the retina, and send the information to be processed to different parts of the brain. With dysfunction of this area, our midbrain does not inhibit the amount of light coming in, which can cause us symptoms like visual snow, ripples, light sensitivity, etc.
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. These functions are closely interconnected, which is why patients with dysautonomia often experience visual changes. Another reason could be that the body has trouble sending enough blood to the eyes. The constriction and dilation of all blood vessels is controlled by the sympathetic nervous system. When this system isn’t working correctly (when there is inappropriate output of the autonomic nervous system), blood might not be properly directed to different parts of the body, including the eyes. This means that the eyes might not get the nutrients, oxygen, and other substances they need to stay healthy.
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 blood to the brain: two carotids (in the front of the neck) and two vertebral arteries (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, which is crucial for blood flow to the eyes. In the eyes, there are special cells called cones and rods. Cones are responsible for detecting colors, while rods help us see in low light. When the blood supply to the eyes is reduced due to issues with these arteries, the cones don't get enough oxygen and nutrients. This can lead to changes in how we perceive colors.
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 three things: 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.
Nystagmus: The majority of the time, nystagmus (inability to focus on an object) and feeling dizzy are due to dysfunction in the brainstem. There is a good nystagmus and bad nystagmus. The good nystagmus is called an optokinetic nystagmus response. This is a reflex that your eyes should have while you are moving about the world. The bad nystagmus is a slow drift of the eyes followed by a quick correction, this is brought out when the eyes are supposed to be maintaining a steady position. With dysautonomia, there may be a diminished optokinetic nystagmus response, a pathological nystagmus found during the examination, or a normal response for both. Nystagmus is commonly seen with vestibular dysfunction, which has neural bodies residing in the brainstem and cerebellum. 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. Finally, in order to feel balanced we need visual, vestibular and proprioceptive input. When one or more of these systems are dysfunctional, we can experience symptoms of dizziness or feeling off balance.
CFNC'S Approach
At CFNC, we evaluate each patient as a whole. This means we look at all aspects of the body as a whole rather than just one isolated system. For example, we evaluate not only the function of the oculomotor system but also the autonomic nervous system, neural timing mechanisms, the cortex, balance, and more.
We focus on the patients’ eyes because eye movements use many different areas of the brain, therefore focusing on the eyes is our best way to get information on the functioning of the whole nervous system. For an overview of overall function, we use a bedside examination. To view more specific aspects of function in finer detail, we use diagnostic tests like a videonystagmography and computerized assessment of postural systems.
Treatment varies from person to person, but may include eye movement therapy. We can use eye movements to exercise parts of the brain that are dysfunctional and causing negative symptoms. If you or a loved one have any questions, please reach out to one of our clinics to schedule a consultation and discuss your individual case.