Internuclear ophthalmoplegia

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dfib slim

dfib slim

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So if you have a lesion in the right abducens nucleus both eyes deviate to the left at rest due to the right lateral rectus and left medial rectus not contracting.

So why with a lesion to the left MLF the left eye stays forward at rest and not deviated to the left? Since the left MLF connects the right abducens nucleus to the left oculomotor nucleus shouldn't a lesion in either the right abducens nucleus or the left MLF lead to the same left eye position at rest?
 
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I'm guessing your body auto-corrects against double vision in the INO scenario, but not in an abducens (or presumably PPRF?) lesion because both eyes are deviating together. That said, I have never heard of the deviation you speak of (regarding the right abducens lesion)-are you sure this is correct? And fwiw I don't think this sort of info matters in the slightest for Step I. Cool that you like digging deeper though.
 
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with a lesion to the left MLF, meaning you cant connect the abducens nerve on the right with the CN3 nucleus on the left. The abducens nerve on the right is still normal, so the right eye will still look to the right initially, brain will interpret this as an error and you'll get the fast component of the nystagmus in the normal eye(right eye) to the opposite side(the left). The left eye stays forward bc of the power of the superior and inferior obliques i believe which are weak abductors will pull it in the foward(central) direciton
 
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dfib slim said:
So if you have a lesion in the right abducens nucleus both eyes deviate to the left at rest due to the right lateral rectus and left medial rectus not contracting.

So why with a lesion to the left MLF the left eye stays forward at rest and not deviated to the left? Since the left MLF connects the right abducens nucleus to the left oculomotor nucleus shouldn't a lesion in either the right abducens nucleus or the left MLF lead to the same left eye position at rest?
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Lesion in OD (right) CN VI -> both eyes will NOT deviate to the left. The OD eye will deviate to the left b/c there's no LR to pull it towards the right. OD eye will also not be able to look to the right when the OS eye is looking; ie no abduction of the OD eye.

Lesion of Left MLF -> this connects the OD LR (CN VI) to the OS MR (CN III) so that when you look towards the right, the OS eye follows the OD eye. With a lesion in the Left MLF (Left INO), the OD eye can still look right, but the OS eye cannot. You will get nystagmus in the OD eye as the CN VI overfires to try to stimulate OS's CN III, but is unable to since there's a lesion in the left MLF. However, at rest, there are no problems with either of the nuclei or their neurons, so they are still innervating their respective muscles LR and MR.
 
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Not to go off topic, but I just noticed that Internuclear Ophthalmoplegia would be a great band name.
 
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syoung said:
Lesion in OD (right) CN VI -> both eyes will NOT deviate to the left. The OD eye will deviate to the left b/c there's no LR to pull it towards the right. OD eye will also not be able to look to the right when the OS eye is looking; ie no abduction of the OD eye.

Lesion of Left MLF -> this connects the OD LR (CN VI) to the OS MR (CN III) so that when you look towards the right, the OS eye follows the OD eye. With a lesion in the Left MLF (Left INO), the OD eye can still look right, but the OS eye cannot. You will get nystagmus in the OD eye as the CN VI overfires to try to stimulate OS's CN III, but is unable to since there's a lesion in the left MLF. However, at rest, there are no problems with either of the nuclei or their neurons, so they are still innervating their respective muscles LR and MR.
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I wasn't referring to a lesion in the abducens nerve which would result in the ipsilateral eye medially deviated at rest. I was referring to a lesion in the abducens nucleus which has inputs to both eyes.

Going down the circuit.
Lesion in the left FEF --> eyes deviated to the left at rest
Lesion in the right PPRF --> eyes deviated to the left at rest
Lesion in the right abducens nucleus --> eyes deviated to the left at rest
Lesion in the left MLF --> eyes straight at rest

I understand the clinical findings with INO and all that jazz, I was just curious about why the resting eye position changes as you progress through the circuit. In my neuroanatomy class we were given hypothetical situations to explain the movements but maybe it was an oversimplification.
 
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err maybe then b/c of the lesion in the CN VI nucleus, there is unopposed traction from the other CN VI nucleus; the nucleus has 2 motor neurons, one for the ipsilateral LR and one that crosses midline to the contralateral occulomotor nucleus to control the contralateral MR

sorry i forgot about the nucleus.
 
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aspiringmd1015 said:
well during rest, arent your eyes in the middle anyways?
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That was the point of my original question. Why the eyes are straight with a MLF lesion and not with any of the others in the pathway. Not step relevant, just curious. I think cs24 correct about the compensation for diplopia.
 
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dfib slim said:
That was the point of my original question. Why the eyes are straight with a MLF lesion and not with any of the others in the pathway. Not step relevant, just curious. I think cs24 correct about the compensation for diplopia.
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did my second reply make sense or no?
 
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syoung said:
did my second reply make sense or no?
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Yes, that's my understanding of an abducens nucleus lesion. My original question was why the MLF lesion doesn't cause the ipsilateral eye to deviate laterally at rest due to the MR getting knocked out.
 
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I think w/ a MLF lesion the MR is NOT knocked out.
Does my first post make sense? I think I spoke about MLF lesion. The MLF only really fires when the ipsilateral eye wants to abduct to pull the contralateral eye adduct (same direction as the ipsilateral one)
 
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Hello all, I am not a doctor I have INO for 7 months now and have been searching the web for help. I was diagnosed by my Neuro Ophthalmologist with INO both eyes and MS. I have not found much if anything for relieving this. I did get three infusions of steroids that stopped the "out of control" dizzy episodes. The infusions have not helped much more. It only seems to be getting worse. Any hope? I do see my MS Neuro on monday, can you offer any advice as to what to ask? Thanks for your time.

Oh cs24 awesome Dr Steve Bruhl avatar
 
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