sethigulshan
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What does frontal eye field do?
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| ssrpk
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conjugate horizontal gaze centres in frontal lobe (Brodman's area 8)
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| sethigulshan
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What happens if there is a lesion of the left frontal eye field. how do you distinguish if you have a right abducent nucleus lesion
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| ssrpk
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vestibulo-ocular reflex remains intact
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| kingsofke
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Conjugate Horizontal Gaze is controlled by PPRF. Which causes eyes to turn ipsilatelly by stimulating ipsilaterla 6th and contralateral 3rd nucleus through MLF. While Frontal eye Field controls CONTRAlateral PPRF so stimulating eyes to look contrallaterally.
So IF ON ATTEMPTED GAZE :- both eyes cant look Lesion is either in ipsilaterla PPRF or Contralarel FEF. (usually if FEF of one side is damaged it will result in over powering of other FEF and causing eyes to deviate towards lesion. If (not usually) lesion of PPRF results in deviation it will be towards lesion.)
what IF ON ATTEMPTED GAZE ONE EYE TURNS OTHER DONT: Well if its an ABDUCTION defect (ie the eye which have to abduct is not moving like right eye in gazing to right ) then its a ABDUCENT nucleus lesion Other WIse if its an ADDUCTION defect (ie left eye not moving to right ) its a MLF lesion (of the left side ).
p.s. it all accounts for CONJUGATe horizontal gaze. not isolated eye movements.
p.p.s Vestibular Nucleus DOES NOT use PPRF to give vestibulo-occular reflex . It controls 3rd and 6th n nucleus on its own (through MLF)
I hope some i was understandable.
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| sethigulshan
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What I meant was if we have a left frontal eye field lesion, the eyes will slowly deviate towards the lesion side. which is left side.( As you said the left frontal eye field should move the eyes towards the right, so in a lesion, there is paralysis of the contralateral lateral gaze and so a secondary effect of that will be the eyes slowly drifting towards the ipsilateral side)
In this scenario, if we have a right abducent nucleus lesion, there is a paralysis of ipsilateral lateral gaze, because there is a an interruption of the supply to the ipsilateral lateral rectus and there is also an interruption of the supply to the contralateral occulomotor nucleus as the pathway thru the MLF is interrupted.
So, in the right abducent nucleus lesion, there is paralysis of right lateral gaze, and so the eyes slowly drift towards the left.
In both the cases, the eyes will be on the left side.
So how do you decide whether it is the left frontal eye field affected or right abducent nucleus?
I hope you get my question?
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| ssrpk
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well, CN VI is closely a/s with PPRF therefore due to the lesion involving PPRF or frontal eye field, there wil be deviation of eyes.
realize tht in case the lesion is in the frontal eye fields, there be loss of contralateral horizontal conjugate gaze (as with PPRF) ;but unlike lesion involving PPRF , CN VI will remain intact in the lesions involiving frontal eye field! Now, tht intact CN VI can be stmulated via vestibulo-ocular reflex through MLF! clearly this will not be the case when the CN VI has been lesioned!
therefore vestibulo-ocular reflex will remain intact in case of lesion involving frontal eye fields!
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| sethigulshan
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ya right, the vestibulo ocular reflex is intact.
well there was another way I was thinking. Tell me how do you perceive this.
Whenever we have a lesion of the frontal eye field, it rarely presents as an isolated lesion, any lesion of this area of the cerebral cortex involves the surrounding areas too, eg the premotor cortex etc. so the lesion will present as contralateral spastic paralysis and ipsilateral lateral gaze paralysis, so the eyes deviate away from the paralysed side of the body.
In Abducent nucleus lesions any strokes of that part of the brain stem are likely to involve the corticospinal tracts too. and if you think logically then it turns out that the eyes deviate towards the paralysed side.
vestibular ocular reflex is of course intact. Thanks for this.
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| sethigulshan
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How do you correlate the slow and fast phases of nystagmus with cerebral cortex or brain stem lesions?
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| ssrpk
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there should'nt be any fast phase of nystagmus in lesions involving cerebral hemisphere, unlike brain stem lesions
by the way, that distinction b/w CN VI and frontal eye field was cool, more likely presentation on the boards!
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| sethigulshan
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ya right, the slow phase of the nystagmus is due to the brainstem and the fast phase is due to the cerebral cortex.
So in brainstem lesions there is no slow phase, so we understand that there should be no fast phase as well. the eyes dont move at all, or they move in all sorts of bizzarre directions.
In cerebral cortex, the slow phase is intact , but there is no fast phase.
You were right. Keep it up!
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