As part of my vision rehab evaluation with patient I always ask about motion sensitivity (or car sickness). The answer can give cues to the functioning of the ambient (magnocellular)visual system.
What is motion sickness?
The semicircular canals within the ears (vestibular system) tell the body that it is motion. The magnocellular visual pathway also “confirms” this motion as movement is observed. But when the system is less aware of magnocellular output (such when one is reading or playing a game in the car) then the vestibular and the magnocellular system get different information. When this happens nausea and rest follow.
The magnocellular system
The magnocellular system is responsible for visual input that affects gait, posture and balance. It also helps us track during reading as it gives the brain the ability to see the line peripherally as the eyes focus on the words being read. There was some discussion that magnocellular problems were associated with dyslexia as well.
Treating the Magnocellular system
To improve 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 toughed. I will have patient do this while wearing glasses with binasal occlusion or base up or down prism depending on posture. This can also be helpful with idiopathic toe walking.
More recently, motion coherence tests have been developed which help to quantify magnocellular function. In these computer based tests, dot 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.
Using the system as tool
The magnocellular system can be a powerful tool in improving posture and balance. The altered visual input quickly re-aligns posture without cueing and makes use of the brain natural ability.