Ways Professionals Test Patients for Vestibular Dysfunction
Have you ever thought about how it's possible to see clearly even though our heads are moving? Most people think that the ears are just for hearing, but actually, there are nerve pathways between our inner ears and our eye muscles which drive our eye movements to keep things stable-looking when the head moves. This is called your Vestibulo-ocular Reflex (VOR). At anything other than very slow speeds, we need our inner ears to give the brain accurate information about head motion so that the brain can, almost instantaneously, tell the eye muscles what to do to keep images looking clear. If this information is not correct, things will appear blurry or jumpy when moving – there is a term for this: oscillopsia.
Try it! Look at a small number or letter at arm’s length in front of you and turn your head slightly back and forth quickly. If your inner ears are working properly, your eyes are being told to move the opposite way of your head movement, at the same speed as the head movement, so that your target still looks clear for you. A normal vestibulo-ocular reflex stabilizes your eyes no matter what movements your head is making.
How Vestibular Rehabilitation Professionals Evaluate the Vestibulo-ocular Reflex
There are ways that vestibular rehabilitation professionals can evaluate this reflex in patients. One is called the Head Thrust or Head Impulse Test. This is where we have you look at a distinct target (often just the tip of the tester’s nose) while the tester gives your head a very small but rapid and unpredictable movement. We look for how well you keep your eyes on the target, and if there is an error in a particular direction of movement, it suggests a problem with the reflex, and helps us figure out what part of the inner ear isn’t doing its job. Testing can also be done by testing what is called Dynamic Visual Acuity (DVA). This is where your ability to read a particular eye chart while the head is not moving, is compared to your ability when the head is being turned back and forth at at least 1 Hz (one back and forth per second). Depending upon how much your ability to read the chart worsens when moving, this can also indicate problems with the vestibulo-ocular reflex (VOR). There are also computerized versions of this type of testing for greater precision.Testing the VOR is only one of many things we evaluate in those with dizziness and balance disorders, but it is a key part of the testing. This is because it can give us an idea whether or not your ears are sending your brain accurate information about your head movements, and if not, how this is affecting your ability to see while you are moving – which is pretty important!
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