apple guava asked in HealthOptical · 1 decade ago

How to isolate out cranial nerve 4 (trochlear nerve) lesion please?

My aim is to show this person who cannot look at their nose, has CN4 lesion.

To look down at your nose, you can use medial rectus to adduct first, then use superior oblique muscle (trochlear nerve) to depress. There, the eyes are looking at nose.

Or you can adduct (again, using medial rectus), then add in inferior rectus to depress. Result the same, looking at your nose.

So if a person cannot look at their nose, it's means CN3 and/or CN4 is/are impaired. Don't which combination but can be just one of them or can be both of them impaired.

Just by asking the person to look at their nose, you cannot isolate out CN4 by itself.

You need another test. For example, when someone is confirmed cannot look at their nose (they get diplopia or whatever), ask now the person to look up and out. To look up and out this, you got to have CN3 intact. Reason being this, to look out and up you can either:

Use your lateral rectus (CN6) + superior rectus (CN3) together. That will look out and up.

OR, you can use "superior oblique CN4 and/or inferior oblique CN3 (to abduct)" then PLUS "superior rectus (CN3) or inferior oblique (still CN3)". This will also get you to look out and up.

In short, you have to have your CN3 intact to look up and out, whatever combination of pulleying you choose to use, CN3 plays a part.

So in summary, if a person cannot look at their nose, this tells me their CN4 may be impaired (but so may their CN3 be impaired also, cannot be sure yet). This test is meaningful under the presupposition that CN3 is intact to adduct the eye into alignment for CN4 to then depress the eye ball. But we cannot just assume things. Need to show that CN3 is indeed intact.

Check if CN3 is indeed intact, by asking the person to look up and out.

Let's say they can indeed do that, this means ie. their CN3 is fine.

So come back to their inability to look at their nose which can be caused by CN3 and/or CN4 lesion, and CN3 is shown now to be fine, therefore their inability to look at nose is due to CN4 alone.

There I've isolated CN4 out.

How does that sound as an approach to isolating out CN4 lesion?

Please comment. Thanks very much. I think I got it right, but just need to double check it with someone good. Thanks.

5 Answers

  • 1 decade ago
    Favorite Answer

    CN 4 supplies superior oblique

    so if SO is paralyzed .....loss of intortion, depression ,abduction,

    due to unopposed action of inferior oblique i think the eye will more adducted elevated i think he can see his nose.......with help of medial rectus

    sorry if am wrong!!!!

  • Anonymous
    4 years ago


    Source(s): Neuropathy Treatment
  • hurd
    Lv 4
    4 years ago

    Trochlear Nerve Lesion

  • Anonymous
    5 years ago

    For any movement - one muscle must contract whilst the other relaxes. If there is a problem with the muscle, both movements will be affected

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  • Anonymous
    1 decade ago

    what the!!?

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