In the field of Functional Neurology, we often say that “the eyes are the window into brainfunction.” This means that how your eyes move and track, how they perceive motion, the shape of your pupils, the response to light as well as ability to hold them steady in the dark and while focusing on a target -all indicate how specific regions of the brain and brainstem are functioning. The eyes are used for assessment as well as treatment in conditions with complaints of dizziness.
Evaluating eye movements in management of dizziness:
To understand how eye movements impact brain function consider the following symptoms below:
Nystagmus, which is a rhythmic and rapid involuntary movement of the eyes, often is seen in cases of patients who complain of dizziness. It contains a slow phase, followed by a quick phase of correction. The nystagmus is labeled by the fast/ correction phase of eye movement.
This nystagmus can be caused by a dysfunction within the inner ear (peripheral) or from the brain (central nervous system). There are many contributing causes to nystagmus and can include BPPV (calcium deposit in an ear canal), congenital contributions, or as a result of sleep deprivation or brain injury and concussion. Most often when nystagmus is present, the patient may complain of vertigo. Vertigo is the perception that the room is spinning and can learn to balance difficulties, risk of falls and injury and overall lower quality of life due to inability to
perform daily tasks of living.
Motion sickness is a common complaint amongst patients sometimes lifelong or post concussion or brain injury. Due to no known treatments for this, patients adapt by learning to live with these symptoms and set limitations on where they sit in the car, how long they spend time in a grocery store or may even limit watching activities that involve fast movements such as sports games. Just as we have reflexes in our arms and legs (ex: patellar reflex) we also have automatic reflexes
in the eye. These Optokinetic Reflexes allow for us to view motion without feeling like we are moving with the target. When performing VNG (Videonystagmography) testing, in patients with reports of motion sickness- often these automatic reflexes do not fire appropriately, fatigue quickly or are overactive.
Gaze stability is the ability to keep your eyes fixed on a target in different positions. This is extremely important in symptoms of dizziness because the patient may present with SWJ (square wave jerks) which are oscillating movements of the eyes while fixed on a target. Even though patients' heads may not be moving, due to the uncontrolled movement of the eyes- motion is perceived which can lead to a variety of symptoms such as eye strain, neck pain, chronic headaches, blurry vision, difficulty with reading comprehension and dizziness.
Impaired Vestibulo-Ocular Reflex:
Vestibulo-Ocular Reflex (VOR) is a reflex we use on a daily basis whether we are walking around, turning around or picking up a dropped object. When we move our head to the L, our eye muscles automatically create an opposite and equal eye movement to the R. This allows us to maintain our balance as well as keeps objects in focus. The impairment of this reflex can be seen in older patients or those with previous brain injuries who are unable to separate head and eye
An impaired VOR is a common cause of oscillopsia. Oscillopsia causes blurred vision and movement based dizziness because when the head is moving, objects appear to be bouncing. The brain perceives motion where there is no motion.
Impaired Cervico-Ocular Reflex:
Cervico-ocular reflex (COR) is responsible for the connection between the cervical spine (neck muscles) and eye movements. This reflex involves the above mentioned reflexes as well (VOR and OPK). This is important to understand in cases where a patient may be complaining of dizziness as well as associated neck pain, neck injury or muscle spasms. The cervical, vestibular and visual systems work together and dysfunction in the communication between these systems
can lead to feelings of dizziness.
The eyes are an important part of any neurological examination, especially when the patient presents with symptoms of dizziness. Dizziness is a complex condition to manage due to the various involved reflexes, pathways in the brain and contributing factors. During a new patient examination at CFNC, the patient is evaluated with diagnostic equipment called VNG (Videonystagmography). This allows us to analyze the eyes in depth by recording in real time to
check eye stability, speed, accuracy, movement and reflexes.