As part of my vision rehab evaluation with a patient I always ask about motion sensitivity (or car sickness). The answer can give cues to the functioning of the ambient (magnocellular) visual system and give us clues as to how well the brain is attending to this information
What is motion sickness?
The semicircular canals within the ears (vestibular system) tell the body that it is motion. The magnocellular visual pathway “confirms” this motion the movement in the peripheral vision also send signals confirming that the organism is in motion and adjust posture appropriately.
But sometimes, the magnocellular input does not agree with the vestibular input. If one is riding in a car and reading or looking at a phone, the brain becomes less aware of the peripheral (magnocellular) input and sends a signal that the body is not moving. This disagrees with the vestibular systems reports of movement forward and so the person may become a bit nauseous. They lift their head and look outside for a few minutes and the two systems once again sync and nausea goes away.
In cruise ship cabin this becomes more difficult as the enclosed cabin may not have a window to help “sync ” the input so systems do not sync and a person gets sick.
Treating the Magnocellular system
To improve awareness of magnocellular input, we do activities on a balance board while performing visual scanning tasks that emphasize keeping the head still and maintaining balance as targets are tough. Patients will do this while wearing glasses with binasal occlusion or base up or down prism depending on posture.
More recently, motion coherence tests have been developed which help to quantify magnocellular function. In these computer-based tests, dots move randomly and the patient must decide which direction most of the dots are moving. Devices like the Neuro-tracker also work on magnocellular function.
Improving Motion Sensitivity
People suffering from chronic motion sensitivity problems may benefit from binasal occlusion or a trip to the neuro optometrist for base in prism glasses. In some, the elimation of no line progressive lenses may help with this as well.