sachin ppt neurophysio of eye movements
TRANSCRIPT
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DR. SACHIN ADUKIA
NEUROPHYSIOLOGY OF
EYE MOVEMENTS
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According to the Hering law of dual innervation, yoked muscles receive equal and simultaneous innervation while their antagonists are inhibited (the Sherrington law of reciprocal inhibition), thereby allowing the eyes to move conjugately and with great precision.
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Medial walls of each orbit - oriented in the sagittal planeLateral walls - oriented at 45 degrees lateral to the sagittal plane. Thus, with the eyes looking straight , axis of orbit is deviated 23 degrees laterally from the axis of the eyeball.
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Oculomotor nerve
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In the Cavernous sinus
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Parasympathetic component
Preganglionic fibres from E-W nucleus synpase in the ciliary ganglion
Post ganglionic fibres in the short ciliary
nerves supply -pupillary sphincter -ciliary muscle
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III Nerve lesion leads to
Deviation of the eyeball down and out
Pupillary dilatation and
Complete ptosis of the eyelid
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TROCHLEAR NERVESupplies the superior oblique muscleNucleus lies in the midbrain at the level of
inferior colliculus near the ventral periaqueductal gray matter.
Only CN to exit the brainstem posteriorlyLongest intracranial course.Has CL innervation
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ABDUCENS NERVE
Supplies lateral rectus muscle of eyeNucleus lies in the floor of 4th th ventricle
within caudal pons.Axons pass ventrally through the pons without
decussating.
COURSEBrainstem - anterior to the pons – pierces the dura overlying basilar portion of occipital bone - Runs up to petrous portion of temporal bone - from its apex, lateral wall of Cavernous sinus.
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INTERNUCLEAR CONNECTIONSMedial Longitudinal Fasciculus. -runs in midline in dorsal tegmentum of brainstem. -extends from midbrain to upper thoracic spinal cord.Coordinates lateral gaze, connects III nerve on one side to CL
VI nerve Nucl.
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Physiological Eye movements
Gaze- horizontal, verticalSaccadesPursuitsVestibuloocular reflexnystagmus- vestibular, optokinetic Disconjugate gazeAccomodation reflex
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Gaze is the coordinated, synergistic movement of both eyes to a target
Directs the projection of a target onto area of highest visual acuity in the retina, the fovea.
Is coordinated by centers in cortex and brainstem, which project to the motor neurons of CNs III, IV, and VI----extraocular muscles
Horizontal gaze center – PPRFLesion in pons leads to deficit in horizontal gaze due to damage of
PPRF.
Vertical gaze center - midbrain reticular formation, pretectal area. Lesion of midbrain leads to deficit in vertical gaze due to damage
these structures.
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Saccades - rapid eye movements that redirect gaze to an object of interest and result in projection of that
object onto fovea.
Saccades- result of cortical and subcortical input to PPRF cortical areas - frontal eye fields (FEFs).
Reflexive saccade or prosaccades - visually guided, in response to external cues. Superior colliculus provides the main input Most superficial layer receives visual input from retina via
lateral geniculate nucleus of thalmus. Deeper layers have motor neurons that project to PPRF and
initiate saccades. sensory and motor are directly linked via synaptic contact
Volitional or intentional saccade- independent of visual stimulus. requires higher order processes like spatial memory, analysis of contextual cues.
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Volitional saccades: 3 typesAnti-saccade:involve making a decision to avert the eyes and
require simultaneous inhibition of the reflexive saccade that would direct the eyes to the stimulus
Memory saccadeCan voluntarily direct gaze to where an object or a
visual cue had beendepend on intact working memory, spatial
orientation.
Predicitve saccadeeye is directed to where target is expected to be
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Smooth pursuit used when tracking a slowly moving object
Aim is to keep that object on the fovea of both eyes
3 questions
Coursecortex---P-C-V---abducen
Cerebellum
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Vestibuloocular reflexVOR rapidly adjusts eye movements to head movements so that gaze can remain fi xed on an object even though the head is moving.
keep an image stable on the retina despite movement.
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Nystagmus Rapid, rhythmic, back-and-forth eye
movements
consists of a rapid component (quick “flick” of eyes) in one direction
And slow component (slow drift) in the opposite direction. is named for the rapid component. MC type- horizontal nystagmus vestibular nystagmus and optokinetic nystagmus, both
physiological. Rotation of the head---- activates vestibular apparatus ---activates
the VOR. When head rotation is greater than what can be compensated by
VOR, the eyes reset with a rapid movement in the same direction as the rotation,
and then compensatory movement of the VOR can happen again. This rapid reset followed by the slow movement mediated by the
VOR; this is vestibular nystagmus
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Caloric testingCOWSCold opposite; warm same
Cold water caloric testing
Hot water caloric testing
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Vertical gaze center
midbrain reticular formation and the pretectal area (just rostral to the superior colliculus)
Anterior portion mediates downgaze,
Posterior portion mediates upgaze
Input - FEFs and visual association areas via superior colliculus
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DISCONJUGATE GAZEConvergence – b/l III nrDivergence - b/l VI nr
Information about an object -near or far – relayed to both occipital lobes via the two lateral geniculate nuclei
In the occipital lobes, the information is integrateddecision to converge (for near objects) or diverge (for far
objects) is made-----relayed to vergence centers in the rostral midbrain near the CN III nucleus.
CN III is activated bilaterally------innervate both medial rectus muscles for convergence, or
CN VI is activated bilaterally------ innervate both lateral rectus muscles for divergence.
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AccommodationConvergence: Both eyes adduct
refractive power of the lens increases by increasing curvature of lens.
Pupils must constrict to increases the depth of field. These 3 components of accommodation response are termed the
NEAR TRIAD.
Accommodation is coordinated through supraoculomotor area (SOA) in the rostral midbrain by sending excitatory projctions
Input- visual cortex
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Lesions of the MLF
INTERNUCLEAR OPHTHALMOPLEGIA
-Eye fails to adduct on the affected side.
-Nystagmus in the abducting eye.
-Causes: Infarction, Demyelination, Syringobulbia, drug toxicity(phenytoin)
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ONE AND A HALF SYNDROME
a conjugate horizontal gaze palsy in one direction and INO in the other
Cause: PPRF or Abducen nucleus and MLF lesion on the same side.
Pontine hemorrhage tumors MS Tuberculoma
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EIGHT AND HALF SYNDROMEOne and half syndrome + LMN Facial weakness
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