supra nuclear eye movement system
TRANSCRIPT
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SUPRANUCLEAR PATH WAYS OF EYE MOVEMENT DR AISHA JEEVAN
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SUPRANUCLEAR EYE MOVT SYSTEM Vestibular system Optokinetic system Smooth pursuit system Saccadic system Vergence system Position maintanace system
Vestibular and optokinetic – head movement
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SUPRANUCLEAR PATHWAY Cortical centre Subcortical centres Vestibular system Cerebellum MLF CORTICAL CENTERS Frontal eye field Supplimentry eye field
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Dorsolateral prefrontal cortexPost eye field
For pursuits
Middle temporal visual areaMiddle superior temporal visual
areaMT pass on to MST---dorsolateral
pontine nuclei---post vermis –flocculus –fastigeal nucleus of cerebellum—medial vest nuclei
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VESTIBULAR SYSTEM Vestibulo- ocular reflex- vestibular
system moves the eyeballs in the opposite direction to the head movt
Latency of about 10 m sec Semicircular canals record angular
acceleration Otolith organs record linear accleration
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CLINICAL TESTING
Caloric test- done by keeping the head flexed at an angle of 30-
Cold water into ext auditory canal- deviation to the same side – nystagmus in opposite direction
Warm water- opposite effect Abnormalities- vertigo; oscillopsia;
abnormal caloric test
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OPTOKINETIC SYSTEMTo hold the images on the retinae
during the sustained head rotation
Reflex get fatiguied after 30 seconds
Optokinetic reflex is tested by using the optokinetic drum or tape
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SMOOTH PURSUIT SYSTEMHelps to keep the image of a
moving object on the fovea constantly
Images moving away from the fovea- stimuli
Cannot follow objects that move faster than 30 or 40 per second
Latency of 125 msecDepend on alertness
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CLINICAL TESTING
Inadequate pursuit by the presence of catch up saccades
Parietal lobe lesion decrease the amplitude and velocity on the side of lesion
Constant drift of eyes to the normal side
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Imbalance of pursuit is seen in cerebellar disease
Loss of ipsilateral pursuit accompanied by “Cogan’s sign of spasticity of gaze”
In post cortical lesions the eye balls are displaced to the side opposite to the lesion
Associated with controlateral homonymous hemianopia and abnormal OKN
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SACCADIC SYSTEM To bring the image of an object quickly
on to the fovea a rapid eye movt- saccade
Visual stimulus; noise can elicit a saccade
Alertness is required Saccadic omission Are ballistic movt Delay 200msec Velocity- 100|sec to 700 \sec
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ANATOMY Pulse-sudden firing of the neurons to
the ocular muscle Step-tonic contraction of the muscle Eye movt is affected by “pulse-step
innervation” Brought by groups of neurons in the
brain stem controlled by higher centers
Excitatory burst neurons ; Pause cells ;Tonic neurons
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EXCITATORY BURST NEURONS
Seen in the PPRF just above the abducent nuclei
The cells for horizontal saccades in the PPRF discharge at high frequencies
Burst cells in the ri MLF in the mesencephalon project to vertical ocular motor neurons to produce vertical saccade
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PAUSE CELLS OR OPNS Located between the abducent nuclei
in the nuclie raphe interpositus They inhibit burst cells Prevent unwanted saccades
TONIC NEURONS Mediated by neural integrator Found just below the abducent nucleus
in the nucleus prepositus hypoglossi and medial vestibular nuclei
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S
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For horizontal saccades –impulses from the abducent n reach the lateral rectus of same side ; controlateral MR through the MLF
For vertical saccades from ri MLF for upwards pass through post commissure and for downward pass directly downwards
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HIGHER CONTROLTwo parallel systems control the
production of saccadesFrontal system- controls the
voluntary gaze-voluntary saccades
Collicular system-control gaze to stimuli appearing in the periphery of the visual fields-reflex saccades
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FRONTAL SYSTEM Impulses from frontal eye field pass
through the ant limb of int capsule; end high PPRF
HORIZONTAL SACCADES – impulses descend along the PPRF to end in the abducent nuclear complexe
VERTICAL SACCADES—reach PPRF ; through para MLF to mesencephalic reticular formation
riMLF coordinates down gaze
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Upgaze is mediated by riMLF and nucleus of Cajal project into the controlateral third n through the post commissure and pretectum
Collicular system
Input from the frontal eye field and parieto –occipital cortex amd output goes to PPRF
Blind sight’- utilises the extrastrial pathway via sup colliculus
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ROLE OF CEREBELLUM
Vestibulo cerebellum –flocculus helps to stabilize gaze holding
Lesion cause post saccadic drift; gaze evoked nystagmus; downbeat nystagmus; rebound nystagmus
Modulus- lesion produce downbeat nystagmus and positional nystagmus
Dorsal vermis and fastigial nucleus-for adjustment of saccadic pulse amplitude
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CLINICAL TESTINGSaccades are tested by asking the
pt to quickly look at a particular direction
Electronystamography- ask to look quickly at the bulb that glows at the extremes of a series of bulbs arranged on a stright line
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ABNORMALITIES OF SACCADE
1. impaired initiation---increased latency Seen in frontal lobe lesions; PSP;
Alzhemier’s disease
2. Abnormal saccadic velocity Fast saccades- in myasthenia slow—lesion involving burst cells
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3. inaccurate saccades under shoot or overshoot seen in lesions of dorsal vermis ; fastigeal
nucleus and brain stem In Wallenberg syndrome- saccades overshoot
to the side of lesion Undershoot away from the side of lesion Post saccadic drift seen in vestibulocerebellar
lesion Hypometric saccades with post saccadic drift
seen in internuclear ophthalmoplegia; myasthenia
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4. Inappropriate saccades (saccadic intrusions) - interferes with visual fixation
a) square wave jerks- it takes the eyes from the target and is followed by a corrective saccade after 200msec
Seen in cerebellar disease and Supranuclear palsy
b) Macrosquare wave jerks- larger amplitude. Seen in MS
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c) Ocular flutter- to and fro horizontal saccades without inter saccadic interval
d) Opsoclonus- similar to flutter but are multidirectional
Due to disorder of pause cellsSeen in encephalitis;
neuroblastoma; tumours and head injury
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VERGENCE SYSTEM To keep the image of an object on the
corresponding points of the fovea by controlling the visual axis of the eyeballs
Convergence with miosis ;accomodation– near triad “
Vergence movts are very slow dysconjugate movts
Latency is 160 msec
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ANATOMY A group of neurons in the
mesencephalic reticular formation ;dorsal and caudal to the third nerve nuclear complex
ABNORMALITIES Convergence is affected by lesions in
the pretectal area It may be associated with pupillary
abnormalities ; upgaze palsy; convergence retraction nystagmus
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POSITION MAINTENANCE SYSTEM To maintain a specific gaze position By rapid micromovts called flicks Slow micromovts called ‘drifts ‘ This system cordinates with other
system The same anatomical pathways for
saccadic and pursuit system
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GAZE PALSIES It can be divided into two types1. Conjugate gaze palsy2. Dysconjugate gaze palsy Conjugate gaze palsya) horizontal gaze palsyb) vertical gaze palsy
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HORIZONTAL GAZE PALSYFrontal lesions produce gaze palsy to the opposite
side eyes are deviated to the side of lesion away from the side of hemiparesis VOR is normal Smooth pursuit is intact
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Pontine lesions gaze palsy to the same side eyes are deviated away from the side
of lesion towards the side of hemiparesis-
“Wrong way eyes” VOR is impaired smooth pursuit is affected
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VERTICAL GAZE PALSYUpgaze palsy seen in lesions in the pretectal
region and post commissure accomodation is usually spared Downgaze saccades and downward
vestibular reflexes are spared Seen in tumours’
hydrocephalus;haemorrhages
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Downgaze palsy it is seen in ventral midbrain lesions
involving ri MLF Ischaemic infarction in that area is the
common cause
Dysconjugate palsy1. inter nuclear ophthalmoplegia2. One and a half syndrome
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Perinaud dorsal midbrain syndrome
Signs:Stright eyes in the primary positionSupranuclear up-gaze palsy defective
convergenceLarge pupilsLid retraction [collier sign ]Convergence retraction nystagmus
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Causes In children – acqueduct
stenosis ;meningitis and pinealoma In young adults –demyelination;
trauma; arteriovenous malformations In elderly- midbrain vascular
accidents;mass lesions
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PROGRESSIVE SUPRANUCLEAR PALSY
Steele –Richardson- Olszewski syndrome
Severe degenerative disease Present in old age Supranuclear gaze palsy affects
downgaze Later upgaze is also affected Horizontal movts get impaired Eventually gaze palsy develops
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THANK YOU