As a patient at CFNC, your initial examination will include a targeted bedside neurological exam and additional in-depth diagnostic testing. As part of the exam and testing, the doctor will be looking at your eye movements. These tests require you to follow the doctor’s finger while it moves and/or follow a target on a screen while you wear VNG goggles. These tests allow the doctors to evaluate how your eyes move.
Why is this important?
Our eyes are one of the best windows into our brain and its function. The doctors at CFNC evaluate your pupil size, how well your eyes constrict and dilate with light, how well they track a target, the speed and accuracy of your eye movements and more.
Our eye movements alone can provide insight to the integrity and function of various areas of the brain, including but not limited to your autonomic system, brain stem, parietal and frontal lobes. At CFNC, oculomotor evaluations are very important and they are a crucial part of the examination process. This blog post will help to increase your understanding of why we look at eye movements on almost every patient and why it is a crucial part of our examination and rehabilitation process.
How do we evaluate eye movements?
In addition to our bedside neurological examination, our new patients will participate in additional diagnostic testing. At CFNC, we use Videonystagmography. This test consists of you wearing goggles and tracking various targets on a screen. In these goggles are tiny infrared cameras and software that provides the doctors with in-depth information about your eye movements.
This test is non-invasive, usually lasts about 12-15 minutes and a neuro assistant or physician will be present with you during the diagnostic testing to guide you through it.
What type of eye movements do we evaluate? And what do they tell us?
Gaze refers to how well your brain can hold your eyes on a target. When evaluating gaze, we are looking at how quickly your eyes will move to the target, how accurately they will land on the target and then how stable the eyes can remain on the target for a period of time.
To initiate the eyes to move to the target requires activation from our frontal cortex, more specifically our prefrontal eye centers. This initiates our eyes to begin a quick movement to the target. To land accurately on the target requires a communication between those prefrontal eye centers and the opposite cerebellum to control the eyes to land on the target. Then, depending on whether we are looking in the vertical plane or horizontal plane dictates other brain areas.
If we are looking up or down, we get information from our frontal eye centers and that communicates to the top of the brainstem at the junction of our thalamus and midbrain.This area has nuclei that send information to the cranial nerves that exit our brainstem and skull that control our eyes to lift up or bring them down.
To look right or left involves the frontal eye centers to communicate with the middle of the brainstem, specifically located in the parapontine reticular formation. This area is closely located with the nuclei that activate the cranial nerves that control horizontal eye movements. Like vertical eye movements, the cerebellum helps to make this movement as accurate as possible. Then keeping the eyes on the target is facilitated by very specific neurons in the pons called omnipause neurons. These specialized neurons facilitate gaze stabilization in conjunction with the cerebellum for gaze in all directions.
Just by assessing gaze, we are evaluating the integrity of the frontal lobe, our upper and middle brainstem and cerebellum. When patients have trouble with gaze this can produce symptoms such as losing your spot when reading, anxiety, headaches, eye strain, tired eyes, etc.
Gaze in Darkness
During the VNG testing, we begin the testing by putting a cover over the VNG goggles, and then have you look straight forward in total darkness. During this test there is no visible target, you are just asked to look straight ahead and hold your eyes still. This allows us to see if your eyes can remain stable with no target.
We can see a couple things with this test: we can see if you are unable to maintain gaze stability and we are able to see if there is any vestibular contamination. Our vestibular system and our visual system work together to complete accurate eye movements relative to our head position. If we do not have any visual targets and our head is neutral, this can bring out a vestibular dysfunction. Common things seen with this test is that the eye will drift in darkness to a side and then re-correct back to center. Patients who have difficulty with the test may experience dizziness, vertigo, anxiety, trouble focusing, difficulty reading, eye strain, headaches, migraines, etc.
Saccade is a verb that derives from the French word meaning to “jerk”. This term was used to describe ballistic eye movements. A saccade is a quick, simultaneous movement of both eyes in one direction to a target. This fast eye movements allow us to take in our environment very quickly. When evaluating saccades, we are looking to see how quickly your eyes begin to move once the target appears in your field of vision (initiation), how quickly your eyes move to the target (velocity), and how accurately your eyes land on the target and stay on the target until it moves again. We evaluate saccadic eye movements both in the horizontal and vertical planes because they utilize different areas of our brain.
Saccade eye movements are generated by our frontal eye centers located in the frontal lobe of the brain. When evaluating horizontal saccades, our frontal eye centers communicate with the pons located in the middle of our brainstem and more specifically the parapontine reticular formation. This area then communicates with the nucleus of our 6th cranial nerve (abducens nerve) which controls the cranial nerve that moves our eyes to the side. This causes the eyes to look from one side to the other. The cerebellum and basal ganglia then work in conjunction with this pathway to make sure the eye movement is smooth and that our eyes land on the target accurately.
In the vertical plane, our saccadic eye movements are generated in the frontal eye fields, similar to the horizontal eye saccades. The frontal eye centers communicate with the posterior aspect of the midbrain and the nuclei of the 3rd cranial nerve (oculomotor nerve), located at the top of the brainstem. This area of the brain communicates with the 3rd cranial nerve which helps to move our eyes up and down. The cerebellum and basal ganglia then help to smoothly move the eyes to the target and to land on the target.
Saccades help us evaluate the integrity and function of the frontal lobe, the basal ganglia, cerebellum, pons, midbrain, 3rd and 6th cranial nerves. Unlike gaze, saccades show us how quickly the brain initiates movement and how fast your eyes are moving to a target. This also allows us to peer into higher cortical areas that control our movement.
Problems with saccade eye movements can result in brain fog, losing your place while reading a sentence, motivation, decision making, etc.
Smooth pursuit eye movements is a term that describes the eyes ability to remain fixated on a target while it moves. These are classified as slow eye movements. Our pursuit mechanisms are produced in our temporal lobe, parietal lobe and occipital lobe. These communicate to the same areas as our saccade eye movements. If we are moving our eyes horizontally, these centers will communicate with our parapontine reticular formation, located in the middle of our brainstem, our cerebellum and the 6th cranial nerve. If we are moving our eyes vertically, these centers will communicate with our midbrain, located at the top of the brainstem, our cerebellum and the 3rd and 4th cranial nerves.
Unlike gaze and saccade eye movements, we are able to evaluate different areas of our cortex such as the temporal, occipital and parietal lobe. These areas of the brain are used for spatial orientation, visual processing and memory centers. When patients have difficulty with pursuits they can experience memory difficulties, spatial awareness difficulties, memory difficulties, reading difficulties, dizziness, etc.
Optokinetic Nystagmus, also referred to as “OPKs,” are eye movements that occur when our field of vision is moving. This is a reflex in our brain that allows our eyes to follow objects in motion while the head is stationary. This consists of the combination of two tracking mechanisms: a smooth pursuit system and an alternate saccade mechanism. When evaluating these reflexes in the brain, it allows us to evaluate all of the areas of the brain we have talked about in addition to our reflexogenic systems.
Pupillary Light Reflex
Have you been to the doctor before and they have shined light in your eyes? This is called a pupillary light test. This test is designed to look at the constriction of your pupils when exposed to light. It is a natural response of the pupils that when exposed to light both of the pupils will constrict for about 2 seconds and then begin to dilate. This response is bilateral even when the light is exposed to one eye.
Not only are we looking to see if your pupils constrict, but as functional neurologists we are looking to see how much they constrict, how fast they constrict, does the eye stay constricted for more than 2 seconds, does the eye exhibit any difficulty with dilating, etc. Looking at how our eyes constrict and dilate and comparing bilaterally can tell us multiple things.
For our eyes to constrict, this is an activation of the parasympathetic nervous system, it is the opposite for dilation (a sympathetic response). If our eyes are having difficulty constricting, this indicates our autonomic integrity and also provides a look into our midbrain function. This is located at the top of the brainstem.
Another example that we see is when eyes constrict very quickly and then tire when trying to dilate in response to light. This is called hipus. This a rhythmic alteration of constriction and dilation in the eye and can indicate fatigue or reach of metabolic threshold for the patient. All of this is very important for providing information about the autonomic nervous system and the midbrain integrity during the examination. Patients who may have an abnormal pupillary light response may exhibit the following symptoms: sensitivity to light, overstimulation with light, headaches, sweating or anxiety when exposed to a lot of light.
The eyes are a window for our brain into the world. As functional neurologists, the eyes are our window to look into the brain and nervous system. Eye movement evaluation is a crucial part of our approach here at CFNC. Based on our findings, we utilize targeted rehabilitation and therapies to help create positive neuroplastic changes to enable healing and correct any eye movement discrepancies that may be found.