E.N.G. Electronystagmography

The Brain has two hemispheres that are not mirror images of each other, neither in structure nor in function.  Any asymmetric output results in aberrant function.  In chiropractic neurology we call this hemisphericity. Obvious examples may be seen in the after effects of stroke or a movement disorder. One side will be seen to tremor, or will demonstrate a characteristic gait or posture, pointing to the origin in the opposite cerebral hemisphere.  These are obvious signs of dysfunction. More subtle problems, such as balance disorders, require indepth knowledge of the nervous system, as well as occasional sophisticated diagnostic equipment to determine the level and location of a functional lesion. 

One of the best and most reliable windows of brain function is seen when examining the opposing reflexogenic constriction and dilatation of the pupils of the eyes in light and in darkness.  With Micromedical RealEyes(tm) one is able to compare and quantify hemispheric asymmetry (hemisphericity) in percentages, by measuring the amplitude and speed of pupillo-constriction (parasympathetic nervous system) in light, and pupillo-dilatation in dark (sympathetic).  The nuclei responsible for constriction of the pupils are located in the midbrain (mesencephalon). They are representative of the reticular activating system, which lights up the entire brain, when functioning normally.  Pupillodilatation is representative of the sympathetic nervous system (“fight – flight” mechanism), which is usually dampened, or inhibited, by the brain via the ipsilateral pontomedullary reticular formation. When we see an inequality of pupillary diameter in either scenario, or a difference in the speed at which one side contracts or dilates, we can conclude an aberrant push – pull relationship between the two systems. This can not always be seen by the naked eye, making this technology invaluable. The test protocol allows for visual observation of the eyes while the patient is in total darkness. Additionally, visual observation allows recording of eye movements in all directions, using infra-red video recordings.

The eyes are also the window to the vestibular system. They provide information about vestibular (balance) function as well as information regarding the ability to generate efficient voluntary eye movement necessary for maintaining visual contact with one’s environment. The peripheral vestibular apparatus consists of matched pairs of sensors that are stimulated by any type of movement, with specific sensors responsible for specific movements. There are six of them, and they are mirror images of each other. There are three on each side in the inner ear, called semicircular canals. They are all perpendicular to each other, so that any movement in any direction will automatically deactivate the opposing sensors on the other side. This is all well and good when they are functioning at the same frequency in a resting state. When this “see – saw” mechanism goes out of balance, a sensory mismatch occurs, and one becomes disoriented.

The vestibular nerves are intimately connected to the the cerebellum and to the muscles that move the eyes. Any prolonged deactivation
(deafferentation) from one side of the body; i.e. an arm in a cast, disuse due to chronic pain, decreased range of motion toward one side when turning the head, repetitive use of ice packs, etc, will alter the frequency of firing to all post synaptic cerebellar pools, including the muscles that move the eyes, resulting in an asymmetric response to head movement, and a probability of dizziness, nausea and / or vertigo. Similarly, the system can be thrown out of balance when habitually repeating the same motion, as in turning the head always to the same side when swimming, allowing one side to become more efficient, with similar results. Oculomotor tests done with computerized ENG analysis software allows for sensitive and documented evaluation of volitional and non-volitional (reflexogenic) movements, such as tracking, smooth pursuit and fixation.