The inner ears are busy sensors. We depend on them for hearing, they let us feel motion sensations, and they help control balance. One of the most important things they do is something most people aren’t aware of: they keep the eyes focused while we are in motion.
Imagine playing a game of ping pong. You have to keep your eyes on the moving ball while at the same time you jump back and forth to intersect it for your shot. This requires two major systems that control eye movements to be perfectly coordinated.
The first system is called smooth pursuit. Your eyes have the ability to track a moving object, like the ping pong ball, but they can only go so fast. At the baseball game, even if you stare hard at the ball when it is hit, it can seem to disappear for a few seconds because it’s moving too fast for your eyes to follow. Then it suddenly reappears far down the field as it slows. The means our pursuit system has limits based on speed and acceleration.
If we’re moving our heads slowly and steadily, we can use pursuit to keep our eyes on target, so that we don’t lose focus as we move. However, if we have to make quick moves, our pursuit ability is not enough because of these limits. That’s when the inner ears come into play.
The semicircular canals, the spinning sensors of the ear, control eye movements in response to head movement. They do this so perfectly that you can jiggle your head back and forth, and the screen will still be easy to read. There is a reflex pathway that tells your eyes to move opposite to your head movement at the precise speed and trajectory that will allow them to remain focused while moving your head. It is a high speed, high acceleration system.
If damage occurs to these pathways, then the focusing system stops working properly. Moving the head quickly can cause the world to shift and vision to smear like a bad video. In people with damage to one inner ear, there is just a small shift with quick head movements. If both ears are damaged, every head movement can cause the world to shift or jiggle. This problem, called oscillopsia, or video-camera vision, means it is hard to chew and read at the same time, or to walk and read a street sign. Every foot step can cause the world to jump up and down. It’s hard to drive on a bumpy road because the world shifts with every bump.
Oscillopsia also occurs when a person is very dizzy, because seeing the room spin is a form of oscillopsia. The room spins because the inner ear sensors tell the eyes to move in response to a spinning feeling. That is normal if the head is moving, but a problem if the head is not—when vertigo is happening.
Blurring of vision with head movement or dizziness is a sign of very serious inner ear damage. It can also happen with some brain balance diseases.
In my next post, I’ll go over how this intersects with balance.