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MBBS II HNNS > L45 - Eye movement > Flashcards

L45 - Eye movement Flashcards

1
Q

Importance of eye movement?

A
  1. Highvisualacuityisrestrictedtothefovea

2. Eyemovementscandirectthefovea to newobjectsofinterest-“foveation”

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2
Q

Pathways for pupillary constriction and dilation?

A

In bright light:

  • parasympathetic stimulation on circular (constrictor) muscle of iris runs circularly
  • pupillary constriction

In dim light,

  • sympathetic stimulation on radial (dilator) muscle of iris runs radially
  • pupillary dilation
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3
Q

List the 5 types of eye movements? Classify into 2 categories?

A

Gaze-shifting movements (voluntary/ attention)
(1)Saccades (2)Smoothpursuit (3)Vergence

Gaze‐stabilizing movements (Reflexive)
(4)Vestibulo‐ocularreflex (5)Optokineticreflex

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4
Q

Innervation of the extraocular muscles?

A

Superior oblique = CN IV Trochlear

Lateral rectus = CN VI Abducens

All the rest: Superior rectus,Inferior rectus, Medial rectus, Inferior oblique = CN III Oculomotor

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5
Q

Describe saccadic eye movement? Is it voluntary or not?

A

Voluntary Rapidmovements ofbotheyes in the same direction betweentwophasesof fixation(conjugateeyemovement)
+
Verysmallmicro‐saccades(involuntary) to prevent fading

Drivenmainlybypositionsignals

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6
Q

Time course of saccadic eye movement?

A

Timecourse:200‐250ms

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7
Q

Describe smooth pursuit movement? Is it voluntary or not?

A

Slow,smootheyemovementsusedtotrackmoving objectsoncefoveation isachieved

Quasi-voluntary:
 Can choose whether or not to track a moving stimulus, but
 Cannot voluntarily generate smooth pursuit in the absence of a moving target

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8
Q

2 basic response phases of smooth pursuit eye movement?

A
  1. Pursuit initiation (= open-loop phase ~0.1s: catchup saccade)
  2. Pursuit maintenance (driven by velocity error / retinal slip: alternative focus + out-of-focus)
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9
Q

Describe Vergence eye movement? Is it voluntary?

A

disconjugate movements used to converge the eyes onto targets at different distances

Reflexive + voluntary components

  • Convergence of lines of sight of each eye to see an object that is nearer
  • Divergence of lines of sight of each eye to see an object that is father away
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10
Q

What drives vergence eye movements?

A

binocular disparity of a target to be fixed

> > align the fovea of each eye with targets located at different distance

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11
Q

Which of the gaze-shifting eye movements are opposite in action?

A

Vergence = Disconjugate eye movement

Saccadic = conjugate eye movement

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12
Q

Function of vestibular-ocular reflex?

A

stabilize the eyes on a target during rapid head movements

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13
Q

Describe the eye movements in vestibular-ocular reflex?

A

Vestibular system detects brief, transient changes in head position

> > Eye moves in opposite direction to head

> > preserves image on the center of visual field

> > physiologic nystagmus

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14
Q

What are the 2 forms of vestibular-ocular reflex and which organs are involved?

A
  1. Rotational VOR: driven by signals from the semi-circular canals which sense head rotations
  2. Translational VOR: driven by signals from the otolith organs which sense linear head acceleration
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15
Q

Describe the reflex arc in vestibulo-ocular reflex?

A
  1. Stimulus = head movement
  2. Afferent = vestibular nerve
  3. Center = vestibular nucleus
  4. Efferent = oculomotor nerves, abducens nerves
  5. Effector = extra-ocular muscles
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16
Q

Describe the neuronal control pathways in the right semi-circular canal when the head turns right?

A

endolymph turns from right to left due to inertia

> > depolarize hair cells
action potential to nerve, Scarpa’s ganglion
medial part of ipsilateral vestibular nucleus
medial longitudinal fasciculus:

Contralateral abducens nucleus (VI) = stimulate contralateral lateral rectus

Ipsilateral oculomotor nucleus (III) = stimulate ipsilateral medial rectus

> > > > > Eyes focus on left

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17
Q

Describe the neuronal control pathways in the left semi-circular canal when the head turns right?

A

endolymph turns from right to left due to inertia

> > hyperpolarize hair cells
less action potential to nerve, Scarpa’s ganglion
medial part of ipsilateral vestibular nucleus
through medial longitudinal fasciculus

Contralateral abducens nucleus (VI) = inhibit contralateral lateral rectus

Ipsilateral oculomotor nucleus (III) = inhibit ipsilateral medial rectus

> > > > > Eyes focus on left

18
Q

Describe the VOR suppression test?

A

Visual fixation on outstretched hands + rotate chair from side-to-side

Normal = eyes remain fixed on outstretched hands

Abnormal = eyes move in opposite direction to rotation with catch-up saccades to re-fix gaze on outstretched hands

19
Q

Describe the Caloric reflex test for comatose patients?

A

 Head tilted back 60o

 horizontal canals of reclining patient are nearly vertical

 Warm water on right causes ampullofugal flow in right horizontal duct = action potential

 Cold water on left causes ampullopetal flow in left horizontal duct = less action potential

20
Q

Function of Optokinetic eye response? Is it voluntary?

A

stabilizetheeyesduringheadmovements

Drivenbyretinaslip(likepursuit)but reflexiveandinvoluntary.

21
Q

Optokinetic eye response work with which other eye movement?

A

TheVORandoptokineticsystems actinacomplementary.

Operateeffectivelyinresponsetoslow (below1Hz)headmovements,wheretheVORhaslowgain.

Together,theykeepthe eyesontarget

22
Q

Describe optokinetic nystagmus?

A

alternatingslowandfastmovement oftheeyesinresponsetoanystimuli

23
Q

Which side of the cortex processes which side of the visual field?

A

Left half of visual cortex receives information from the right half of the visual field/ left half of retinal yield of both eyes

Right half of the cortex receives information from the left half of the visual field/ right half of retinal field of both eyes

24
Q

Describe the motor neuronal activity in saccadic eye movement? (think is the AP constant?)

A

‘Burst-tonic’ neuronal firing pattern

Abducens neuron fires a burst of activity that precedes the movement > move eye into position

In between saccades, these neurons have tonic firing > maintain static eye position

25
Q

Which 3mainbrainareasare involvedinselectingvisual targetsforsaccadesand planningthemovements?

A

(a)Superiorcolliculus (b)Frontaleyefields (c)Lateralintraparietalarea

26
Q

What are the 2 ‘fields’ processed in the visual pathway brain regions?

A

spatially overlapping:

(a) Visual receptive field: region of space in which visual stimuli activate cell
(b) Movement field: a region of the visual field for which the neuron responds BEFORE execution of a saccadic eye movement

27
Q

Compare the brain areas that modulate visual signals vs sensory and attentional signals?

A
  • Visualsignals = dorsalspatialvisionpathway in occipital lobe
  • Sensoryandattentionalsignals = frontaleyefield near frontal lobe
  • Initiation andcoordinationofeyemovement = superiorcolliculus + oculomotorcentersinreticular formation +vestibularnuclei
28
Q

Describe the place code for saccade vectors and the 3 types of neuronal response to onset of visual target?

A

InSC,FEF,thesaccadevectorproducedbymicrostimulation
=sameindependentof startingeyeposition

3typesofresponsesofneuronsinallthreeareas
(a)Visualneurons: respondbrisklytoonset

(b) Visual/movementneurons: brisk responsetovisualtarget+burstof activitybeginningrightbeforesaccade
(c) Movementneurons: novisualresponsebut clearburstofactivityaroundsaccade

29
Q

Describe the visual neuron response to onset of visual target? Activity before saccadic eye movement?

A

respondbrisklytoonsetof visualtargetinreceptivefield

Noburstofactivityaroundtimeofsaccade

30
Q

Describe the visual/ movement neuron response to onset of visual target? Activity before saccadic eye movement?

A

brisk responsetovisualtargetandalsoburstof activitybeginningrightbeforesaccade

31
Q

Describe the movement neuron response to onset of movement target? Activity before saccadic eye movement?

A

novisualresponsebut clearburstofactivityaroundsaccade

32
Q

Relate the layers of the superior colliculus to the neurons involved in saccadic eye movement

A 
Superficial = visual neurons 
Intermediate = Visual/ movement neuron 
Deep = movement neuron
33
Q

Which brain area do saccade planning and generation?

A

Superior colliculus = planning the particular metrics (amplitude, direction)of a saccade.

Frontal eye field = higher level role in target selection for saccade

34
Q

Damage to one of SC or FEF causes permanent loss of saccadic eye movement. T or F?

A

False
Lesions made to the SC alone or the FEF alone cause transient deficits with saccades, but these largely recover

lesions are made to both SC and FEF = permanent loss

35
Q

Frontal eye field send signals to which brain region for processing horizontal movement?

A

Horizontalmovement–ParamedianPontine ReticularFormation(PPRF)

2 pathways:
1) Indirect:byprojectionstotheipsilateral SuperiorColliculus,whichinturnprojectsto thecontralateralPPRF.

2)Direct:byprojectionstothecontralateral PPRF

36
Q

Describe outflow tracts of the Paramedian Pontine Reticular Formation. (For horizontal eye movement)

A

1) Ipsilateral Lateral rectus (abducen)

2) Medial longitudinal fascilulus > Contralateral oculomotor nucleus > Contralateral Medial rectus

37
Q

Part of brain affected: Gazetotheright impaired.

A

Lesion upstream to right abducens nucleus

38
Q

Part of brain affected: Impairedadductionof lefteye.

A

Lesion in left medial longitudinal fasciculus

39
Q

Part of brain affected: Impairedadductionof lefteyeandptosis.

A

oculomotor nerve palsy (common)

40
Q

Part of brain affected: Eyescannotbemovedto right.Intactleftpontine centermoveseyestoleft

A

Lesion upstream to right pontine gaze center

41
Q

Which brain area integrates sensory input (sound, vision)?

A

Angular gyrus of parietal-temporal-occipital association cortex

MBBS II HNNS (57 decks)

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