Cheatography
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CN III, IV, IV and their disorders
This is a draft cheat sheet. It is a work in progress and is not finished yet.
CN III
Pathway: |
Nucleus in ventral periaqueductal grey matter @ superior colliculus |
Nerve passes through interpenducular cistern to PCA into cavernous sinus (lateral wall) |
Passes into orbit, divides into superior + inferior branches |
Dysfunction S&S
Eye is down and out with pupil dilation + ptosis |
Patient cannot move eye up and in |
Diplopia is greatest when patient moves eye towards weak side |
Concomitant vs Paralytic Squint
Concomitant |
Paralytic |
Congenital |
Affected eye shows limited movement |
NO DIPLOPIA |
Angle of eye deviation + diplopia greatest when looking in the direction controlled by the weak muscle |
Extraoccular muscles + nerves intact |
Outer image always produced by the weak eye |
Full movement of eyes when tested seperately |
DIPLOPIA IS ALWAYS PRESENT |
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Head tilt posture present in opposite direction to eye - minimises diplopia |
CN IV
Pathway: |
Nucleus @ midbrain- level of inferior colliculus near ventral periaqueductal grey matter |
Decussates in dorsal aspect of BS |
Emerges laterally around cerebral peduncle |
Enters into the cavernous sinus (lateral wall) |
Passes through superior orbital fissure |
Dysfunction S&S
Eye up and in |
Pt cannot move eye down and out |
Diplopia is greatest when patient moves eye towards weak side |
Disorders of Gaze
Seizures |
During a seizure, the eyes deviate towards affected limbs in a jerking fashion |
Themipareisis |
Tonic deviation of eyes away from hemiparetic limb |
Lesion in frontal lobe, ipsilateral to direction of eye |
Damage to PPRF |
Tonic deviation of eyes towards |
Lesion in pons, contralateral to direction of eye |
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Vertical gaze palsy |
Midbrain/pontine lesions |
Perinaud syndrome |
Impaired upwards eye movements, convergence, response to light + accommondation impaired |
Dorsal midbrain lesion - IIIrd Ventricle tumour, pineal region tumours, hydrocephalus, wenicke's encephalopathy, encephalitis |
**Internuclear ophthalmologia |
Disconjugate gaze palsy, sawtooth nystagmus (back and forth) |
Damage to ML bundle, MS |
Webino |
Bilateral IOP + exotropia + loss of convergence, conjugate gaze palsy to one side |
Midbrain lesion, PPRF/abducens nucleus + adjacent ML bundle |
Occular apraxia |
Does not move to command but has ful range of random eye movements |
Bilateral prefrontal motor cortex damage |
CN VI
Pathway: |
Floor of IV ventricle |
Axons pass ventrally through pons, overlies basilar portion of occupital bone |
Runs up petrous part of temporal bone |
Enters lateral wall of cavernous sinus |
Thin nerve, very vulnerable to increased ICP + superior pressure from tentorial cerebellar lesions |
Dysfunction S&S
Can occur with CN III palsy |
Eye position would be medial |
Pt would not be able to move eye outwards |
Diplopia is greatest when patient moves eye towards weak side |
Eye movements
Middle gyrus of frontal lobe |
Fast rapid eye movements |
Occipital cortex |
Slow movement of eyes to ipsilateral side |
Frontal + Occipito-mesencephalic pathway |
Project to III, IV, VI nucleus |
Pursuit |
Slow movement that fixed image on macular area |
Saccadic |
Rapid - aligns new target on macular area |
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