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Athletic development specialists dedicated to the art and science of excellence in movement

The Eyes Have It Part II: Cranial Nerves and Movement Implications

Go HERE for Part I.

Vision is largely an underexploited territory in the athletic performance world.   Through our work with Paralympians and other specialized populations, we’ve been fortunate to team with vision professionals and other “non-athletic” therapists to help bridge the gap between medicine and performance.  The great thing about vision is that organic vision improvements come with very little need for physical recovery and have nearly zero risk of injury.   

Consider this summary from Henriques (2001) when describing the interaction of the body and eyes during a reaching task…

The brain uses information about body geometry to guide movements. When you reach for an object, vision may reveal that your hand is 20° right of its target, but this information alone cannot tell you how you should move your joints, or whether you should activate or relax various muscles. For that, you also need proprioceptive or motor information about the current angles of your eyeball, your head, and your arm joints, as well as stored data about the geometry of the bones and muscles in the linkage from eyeball to fingers. The brain must contain a representation, or model, of body geometry.

Understanding vision’s role begins with reviewing our cranial nerves.  There are twelve types of cranial nerves, all of which factor in the equation at least indirectly, but here we’ll focus on three.

Optic (II).  The optic nerve is directly responsible for transmitting visual images to the brain. 

Vagus (X) – Containing parasympathetic nerve fibers, the vagus nerves are responsible for heart rate, breathing, digestion.

Accessory (XI) – These innervate the sternocleidomastoid (responsible for rotating the head), and upper trapezius (flexion and extension of neck), shoulder movements. 

Using vision is encoded into our primitive movement habits (Clopton 2002) (see for example, the Asymmetric Tonic Neck Reflex).  More graphically, if you see a giant ball rolling toward you in the temple of doom your eyes will signal the brain that it’s high time to mobilize a sympathetic nervous system response.  This an extreme example of the vision driving the nervous system, which in turn drives a musculoskeletal response…if you don’t want to get rolled over!

However, in working with completely blind athletes, it’s clear they don’t have the same visual stressors we have.  They may have stressors from balance, sound, temperature, but things that can’t be seen simply won’t change these individuals’ nervous state.  In contrast, partially blind athletes often have heightened visual stress, since they can see just barely enough to be emotionally affected by their incomplete perspective.  Lacking a complete visual of the world can add a constant low grade of stress to the nervous system. 

For the rest of us, many eye issues don’t arise to the level of clinical impairment.  Convergence, alignment, and symmetry are a few other issues that affect our visual state yet can still be improved through visual treatments.  Many forget we actually have reflex programming that predisposes us to seek levelness in our world.  Without us consciously thinking about it, the brain will automatically seek to restore levelness and clarity (Troiani 2005).  To accomplish this task, we’ll call on the muscles in the head, neck eyes, muscles of respiration, and pretty much anything else connected to these (aka, the whole body!).  Set your computer at an awkward angle and/or look behind a set of misfit glasses…how does your neck feel?

What does this have to do with the other nerves?  Start with the vagus nerve…imagine going through life with the world twisted on its side due to a visual dysfunction.  How well do you think you’d control emotions?  Probably get a bit frustrated…(perhaps for another day we can discuss the burgeoning research linking ADD as a VISION problem!...yes, that’s correct, rather than drugging kids up with Ritalin..what they really need is an eye professional who specializes in developmental conditions and not someone who’s just going to slap a set of contacts on them!).   What happens when we get frustrated…heart rate, breathing, and digestion are affected in some way. 

Let’s not forget the accessory nerves, which control head and neck movements.  Let’s say you’re constantly trying to tilt your head one way or bend it forward or backward to get the world into your center of vision (gets even trickier if the eyes are significantly asymmetrical…).  How well do you think the structures of your head, neck, and jaw would like being balanced perpetually off center?  And since we know the entire body is connected, any deviations in these structures when repeated for days, weeks, months, and years can have cascading effects down the body, especially into the shoulders.

The effects are not limited to resting position.  An athlete trying to perform a task will constantly.  What are often seen as musculoskeletal faults (“bad form”) may actually be compensatory movements.  This is particularly noteworthy in running.  Ultimately, it bespeaks the hubris of some “biomechanics” coaches who think you can fix form simply by looking at structure.  Likewise, many therapists (or wannabe therapists) would have us endlessly mashing on noncompliant tissues to remove restrictions, when in fact the real “restriction” may be some higher level sensory input from the eyes requiring compensations at the musculoskeletal level. 

Conclusion

Unless addressed, eye mechanics can have a profound effect on overall body movement and psychology.  That’s fine if nothing is wrong, but if underlying conditions are not addressed there may be implications elsewhere.   Admittedly, these are not always obvious problems, but neither is a slow leak in a wall or dam.  It is the accumulation of low grade stress that can impair resting neurological state and the ability to optimally acquire higher level skills.  Keep the sensory component at the forefront when choosing among interventions. 

References

Henriques DY, Crawford JD.  Role of eye, head, and shoulder geometry in the planning of accurate arm movements.  J Neurophysiol. 2002 Apr;87(4):1677-85.

Clopton, N, Duvall, T, Ellis, B, Musser, M, Varhese, S. Investigation of Trunk and Extremity Movement Associated With Passive Head Turning in Newborns.  PHYS THER. 2000; 80:152-159.

Troiani D, Ferraresi A, Manni E.  Head-body righting reflex from the supine position and preparatory eye movements.  Acta Otolaryngol. 2005 May;125(5):499-502.

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