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question: abduction of the eye

Discussion in 'Step I' started by fizzbot, May 11, 2007.

  1. fizzbot

    fizzbot Member
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    The S.O. muscle abduct, introverts, and depresses the eye. Yet in FA it appears the the eye looks medially with the help of the superior oblique. I am a little confused, what exactly does abduction and adduction of the eye mean?
     
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  3. TheEleventhReel

    TheEleventhReel Dinkin flicka
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    The oblique muscles can be very confusing. Yes, the SO does all those things, but what it looks like clinically is that the SO rolls your eye down and in (like trying to look at your right nipple w/your left eye). Abduction and adduction are the same as with your appendages. For instance, in your left eye, the lateral rectus muscle will ABduct your left eye as if you were trying to look at your left ear. The medial rectus muscle of your left eye will ADduct your eye, as if helping you look at the bridge of your nose.
     
  4. rice_boy

    rice_boy Member
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    ^ I think the confusion here is what the SO does solely on its own and what it does in combination with the rest of the eye musculature.

    The combination of medial rectus + SO causes the eye to ADduct. This is what is shown in FA ( i assume).
     
  5. fizzbot

    fizzbot Member
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    ya but it looks like the arrow going into the eye is just labeled "SO" only, so the SO depresses, abducts, and introverts I guess they are showing us it introverts more than abducts and thus makes you look medially?
     
  6. blz

    blz Senior Member
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    Really the eye muscles involves some pretty deep physics and vector addition because the muscles are aligned in different axises. Plus, when you move certain groups, the brain automatically suppresses antagonists. What I would know about the eye are the main functions of each individual eye muscle and how you test them using the cardinal directions. The cardinal directions are just points in space that align a certain extraocular muscle in an axis that results in that muscle being the predominately used muscle.

    just a recap:

    medial rectus (MR)—
    moves the eye inward, toward the nose (adduction)

    lateral rectus (LR)—
    moves the eye outward, away from the nose (abduction)

    superior rectus (SR)—
    primarily moves the eye upward (elevation)
    secondarily rotates the top of the eye toward the nose (intorsion)
    tertiarily moves the eye inward (adduction)

    inferior rectus (IR)—
    primarily moves the eye downward (depression)
    secondarily rotates the top of the eye away from the nose (extorsion)
    tertiarily moves the eye inward (adduction)

    superior oblique (SO)—
    primarily rotates the top of the eye toward the nose (intorsion)
    secondarily moves the eye downward (depression)
    tertiarily moves the eye outward (abduction)

    inferior oblique (IO)—
    primarily rotates the top of the eye away from the nose (extorsion)
    secondarily moves the eye upward (elevation)
    tertiarily moves the eye outward (abduction)


    also, the SO and IO are used solely to depress and elevate the ADDUCTED eye (that's why you bring the penlight medially to test the function of the obliques). likewise, the IR and the SR are used to depress and elevate the ABDUCTED eye.

    Also, pay attention to how 4th (vertical diplopia, head tillted to side opposite palsied eye), 3rd (ptosis, down and out), and 6th nerve palsy (adducted palsied eye) present and what would likely cause each injury. Don't forget about the role of the abducens nucleus and the MLF in conjugate gaze - injuries involving this system resulting in internuclear opthalmoplegia (common in MS).
     
  7. fizzbot

    fizzbot Member
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    you are one of the nicest people on here, i hope you absolutely crush the boards.

    Also, so I guess the cardinal directions are flipped in terms of medial and lateral for the SR, IR, SO, IO (ie the SO ABducts and depresses yet the cardinal directions to test it in is MEDIAL and inferiorly).
     
  8. blz

    blz Senior Member
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    yea just remember when you adduct the eye, the SO and IO are aligned in a new axis in which they are the only muscles used to depress and elevate the eyes. it all really just has to do with the physics of the vectors.
     
  9. w0ggy

    w0ggy New Member

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    I was getting confused myself, but as it turns out, it's actually an error in FA...hopefully this helps...

    "345--swap SR with IO at the top, and IR with SO at the bottom"

    http://forums.studentdoctor.net/showthread.php?t=282105&highlight=aid+2006+errata
     
  10. blz

    blz Senior Member
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  11. theTruth_97

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    this is bringing up a really old thread.....but to make sure I actually understand it- so if I wanted to test a patients Left Superior Rectus muscle functional ability then I would have them look towards the left and up?
     
  12. pd1112

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  13. FlashTime_91

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    thanks for bringing up this old thread! very useful
     

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