Author: Dr. Aaron Nichols
Excel Neuro-Optometric Clinic
Do you experience motion sickness while driving a car or motorcycle, or riding as a passenger?
Motion sickness is a common problem experienced after a traumatic brain injury (TBI) and can be felt during various activities that require you to shift focus from close to far objects.
Everyday activities that may cause motion sickness include:
- Riding as a passenger
- Reading in the car, train, or bus
What causes motion-sickness?
The balance mechanism in our brain is built on three systems:
- Vestibular (balance)
- Somatosensory (proprioceptive, touch feedback)
With specific regards to the visual system, our brain processes vision through two pathways:
- Parvocellular – central “focal” vision, or visual acuity
- Magnocellular – ambient vision, or peripheral side vision.
In particular, the magnocellular system communicates neurologically with the vestibular system telling us “where” we are in space, which is necessary to keep us balanced while walking or moving, and even driving.
The magnocellular system is sensitive to motion, and following a brain injury, or a concussion, our magnocellular pathway is often affected.
When this happens, our threshold is lowered and our sensitivity to processing our side vision, particularly motion, becomes higher.
When this part of the visual system is damaged, the patient can feel out of balance with their surroundings.
A term for this is “focal binding”, where the patient has trouble with their magnocellular pathway (peripheral) and uses more of their parvocellular pathway (focal). This mismatch can cause difficulty with walking, driving, and even just moving their head.
Often, patients may receive one form of therapy, such as vestibular therapy, and then hit a plateau, where their improvement does not seem to be increasing. This may be because their visual system is not functioning properly, and creating a barrier for other professionals to fully rehabilitate the patient.
Given that the systems work together in the brain, it is important to determine the etiology of the symptoms, in order to properly create a therapy program or proper referral.
In order to fully understand how your visual system is functioning, a comprehensive binocular vision assessment should be completed by an optometrist who is trained in neuro-optometric rehabilitation or optometric vision therapy.
Optometrists with specific post-graduate training in this field are able to assess the patient’s complaints, and determine if the problem is visual, vestibular, or a combination of visual-vestibular.