DR. SACHIN ADUKIA

NEUROPHYSIOLOGY OF

EYE MOVEMENTS

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.

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.

Oculomotor nerve

In the Cavernous sinus

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

III Nerve lesion leads to

Deviation of the eyeball down and out

Pupillary dilatation and

Complete ptosis of the eyelid

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

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.

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.

Physiological Eye movements

Gaze- horizontal, verticalSaccadesPursuitsVestibuloocular reflexnystagmus- vestibular, optokinetic Disconjugate gazeAccomodation reflex

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.

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.

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

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

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.

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

Caloric testingCOWSCold opposite; warm same

Cold water caloric testing

Hot water caloric testing

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

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.

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

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)

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

EIGHT AND HALF SYNDROMEOne and half syndrome + LMN Facial weakness

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