Eye movements and Vertigo

One of the reflexes connected with balance is not learned, it is present at birth. That is the automatic control of eye movements during head turns, known as the the vestibulo-ocular reflex. In health, if you turn your head, your vision does not normally turn into a blur. You will focus very briefly on one view, then another, then another, until you have completed the head turn. To do this requires rapid, accurately controlled eye movements. Eye movements are controlled by muscle activity, under the control of an image stabilization system which receives information from the inner ear. There are good survival reasons why we have evolved this system. If you are a monkey swinging through the trees, you need to keep the ability to focus on the next branch while moving. Otherwise, pretty soon you'll be a dead monkey.
The control of eye movements is assisted by predictive reflexes from the inner ear balance organ.
If the brain receives a signal that you are turning rapidly to the right, it will automatically trigger a series of reflex actions designed to keep your vision in focus.
Your eyes will sweep across from right to left, at the same rotational speed as the surroundings, helping them to fixate on one point in the rotating view.
Just before the eyes reach their limit of movement within the eye socket, they are then sent flicking very fast to the right - much faster than the speed of rotation. For this split second only (instead of the whole length of time of the head turn) vision would be blurred.
The eyes then start another sweep to the left.
This repetitive horizontal jerking movement of the eyes, with a slow phase to one side and a fast phase to the opposite, is called nystagmus.
Nystagmus can be seen in normal life if you are sitting on a roundabout.
Nystagmus is usually seen in patients suffering acutely from vertigo.
If you have nystagmus, it will look to you as though your surroundings really are moving.
As well as the inner ear telling you that you are spinning, if you look at your surroundings with nystagmus, your eyes confirm that either you or the world around you is spinning.
Because the reflex control of eye movements is built in to the brainstem at such a low level, it can be difficult to stop nystagmus and vertigo from happening during very rapid head turns in someone with a damaged inner ear.
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