Oculomotor (eye movement) dysfunction provides a precise window into central and peripheral nervous system pathology. Videonystagmography (VNG) assesses several types of eye movements including pursuits, saccades, optokinetics, and involuntary nystagmus (to-and-fro movements of the eyes at rest). These eye movements are intimately related to the functionality of specific regions of the brain. For example, upon recording the speed (velocity) and acceleration (latency) of a saccadic eye movement (rapid jerk-like movement of the eye that redirects the visual axis to a new location) we can determine if any functional deficiencies lie in the frontal lobes of the brain. Therefore, the practitioner has an objective number which to compare to after treatment to ascertain the degree of improvement.
What is Video Nystagmography?
Video Nystagmography testing (VNG) is the gold standard in the assessment of physiological lesions in the central nervous system and the vestibular system. The examination protocol itself involves a series of tests designed to ascertain the ability of a person to follow visual objects with the eyes. Each test incorporates a different type of eye movement that is known to be a direct indicator of a specific region within the brain. For example, when testing saccades (eye movements in which the eyes jump from target to target) we know that the area of the brain being measured is the frontal lobe. Another example would be putting the individual in what is termed a Dix-Hallpike maneuver (rapidly moving the head from an upright position when seated to a head hanging position with the individual lying on their back and head off the table with one ear 45 degrees to the side) and looking at the position of the eyes. We know that there should not be any spontaneity of eye movement in this position and if there is so it is an indicator of a calcium carbonate crystal in the inner ear and thus benign paroxysmal positional vertigo (BPPV). All of this information is of upmost importance to the chiropractic neurologist because it allows for pin-point diagnostics as to what side the problem is on and where in the brain the problem can be found. Therapeutic outcomes are subsequently improved drastically.
Why is a VNG Assessment Necessary?
The information from the VNG assessment and from the other diagnostic tests utilized at the Conde Center is gathered and a working, functional diagnosis is generated. A targeted treatment plan is then created with emphasis on the deficient regions of the brain. The goal is to promote neuroplasticity, the brain’s ability to reorganize itself by forming new neural connections in response to targeted stimuli, in the areas that are under functioning. Thus, a patient presenting to our clinic after having suffered a stroke may exhibit positive VNG test results exhibited as dysmetric (lack of coordination) pursuit eye movements. The coordination of the pursuit eye movement system is reflective of activity in the parietal lobes and the cerebellum. After proper rehabilitation of these regions, reexamination utilizing the VNG should demonstrate normal pursuits.