Extraocular Muscles

Written by Travis M. Moore
Last edited 16-Feb-2021

The Eyes Have It

Wondering why there's an entire module on eye muscles in an audiology guide? What do eye muscles have to do with hearing? First of all, there actually is a connection between eye muscles and hearing. Think spatial hearing. If you're in the woods and you hear a branch snap, what do you do? You focus your eyes in the direction of the sound without even thinking about it. So yes, there are connections between the auditory system and the ocular motor system. But this isn't really why we care about eye muscles as clinicians.

The truth is, the main reason we study eye muscles as audiologists has more to do with balance and vision than hearing. Thought audiology only dealt with hearing? It turns out there's an entirely separate system attached to the cochlea in the inner ear that senses our movements: the vestibular system. The vestibular system senses angular motion (turning), linear motion (going forward and backward), and tilt. Our vestibular system contributes to our sense of balance.

What is perhaps not emphasized enough is that the vestibular system is also vital to proper vision. Not in the sense of processing visual information, but in the sense of keeping objects in focus. Here is where the extraocular muscles come into play. Because the vestibular system is sensitive to motion, it can automatically adjust the position of our eyes to keep objects on the most sensitive part of the retina (the fovea). We don't have to think about these movements. When we walk our heads bob up and down, yet we can maintain a clear image because the vestibular system adjusts our eyes as we bob. In fact, because the visual system has reflexive control over our eye muscles, eye movements are a great way to measure the health of the vestibular system.

As discussed in the Vestibular Assessment module, the vast majority of the test battery for assessing the vestibular system is done indirectly through measuring eye movements in response to vestibular stimulation. Therefore, it is extremely important that the vestibular clinician understand the muscles that move the eyes: the extraocular muscles. In this module, we'll cover the basic anatomy, as well as some important laws governing how the eyes move and the cranial nerve nuclei responsible for initializing eye movements.

Extraocular Muscles