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13 Cards in this Set
- Front
- Back
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abnormal, jerky pursits (saccadic pursuits) are generally localized to
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lesion in the ipsilateral parietal-occipital-temporal lobe
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where are saccades initiated
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frontal eye field
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Describe the pathway of signals used to complete a saccad to the right
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1. left eye field sends impulse to Right PPRF 2. Right PPRF sends signal to a)Right abducent nerve to right lateral rectuus and b)Right abducent nucleus to left oculomotor nuclus via the left MLF to left medial rectus\
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Where would a patients eyes deviate if an eye field is hypoactive.
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Towards the affected eye FIELD. For example, if the left field is hypoactive, the right field will signal to the left PPRF which will activate the left lateral rectus (via the left abducent nucleus) and the right medial redctus (left abducent, right MLF, right CN III). This will cause the eyes to deviate towards the left
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IN which directions would a patient's eyes deviate if an eye field is hyperactive
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Away from the affected eye field. For example, if the left field is hyperactive, it will send impulses to the right PPRF. The right PPRF will signal the right abducent nucleus which will activate the right lateral rectus and the left medial rectus (via the right abucent and left MLF). This will cause the eye to look right, away from the affected eye.
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What structures are damaged in "right away eyes". What might cause this lesion
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Damged to the ipsilateral frontal eye field and motor cortex usually lesions of the cerebral hemisphere. For example, damage to the left side would lead cause the eyes to deviate to the left (because the right field takes over activating the left PPRF and the left abducent =>left lateral rectus, right medial rectus). there would also be damage to the left motor cortex causing right hemiparesis
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what structures are damged in "wrong way eyes"
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Eyes are deviated right and right hemiparesis. A lesion in CN6 or PPRF causes the eye deviation and cortical spinal tract casues hemiparesis. This pattern may be caused by a pontine lesion, thalamic hemorhhage (deep coma) or seizure disorder
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What strucutres would you expect to be damaged if a pt has wrong way eyes right eye deviation, right hemiparesis
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Since the eyes are looking right and the right side is paralyzed you know the left cortical spinal tract is dmaged and the left CN6 or PPRF is damaged
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How can damage beteween the abducent and PPRF be distinguished
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Check the VOR, if the VOR is intact you know CN6 is working so the lesion must be in the PPRF
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What is the cause of ION? What sxs are expected?
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ION is caused by a lesion in the MLF. You would expect the ipsilateral eye to not fully adduct due to interuption of the signal to the medial rectus. You could also see nystagmus of the contralateral eye. Note that ION is named for the side of wak adduction. Can be caused by MS, plaques, pontine infarct
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What sxs would you expect with an isloated lesion of the CN6 nucleus
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Ipsilateral lateral gaze palsy. For example if you lesion the right abducent nucleus you will lose signal to the right lateral rectus and the left medial rectus, imparing you ability to look right. The VOR will also be messed up.
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What lesion produces 1 1/2 syndrome? What sxs are expected
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Leson of the MLF and abducent nucleus on one side. The ipsilateral eye cannot move laterally at all and teh contralateral eye can only ABduct. For example if you have a lesion of the right MLF and abducent you will lose the ability to ADduct your right eye because of disruption of the right MLF and signals from left abducents to the right medial recuts. you will lose the ability to ADDuct your right eye because of disruption of the signals to the right lateral rectus form the right abducents. You will not be able to ABduct the left eye because of loss of signals to the left medial rectus from the right abducents via the left MFL. ABduct of the left eye is ok because the left abducent is ok
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What is the common cause of locked in syndrome? What structures are usually damaged
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usually an infarct in the anterior pons. damage to the corticospinal tracts and CN6 nerve fascicles. CNs 3 and 4 and the reticular formation in the posterior brainstem are ok. The patient is away but completley paralyzed except for upward and downward eye movement
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