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LCRS 2 > Visual Pathways and Control of Eye Movements > Flashcards

Visual Pathways and Control of Eye Movements Flashcards

1
Q

Where do retinal ganglion axons coming down the optic nerve synapse?

A

Lateral Geniculate Nucleus

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2
Q

Where is the lateral geniculate nucleus found?

A

Thalamus

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3
Q

What are the fibres leaving the lateral geniculate nucleus called?

A

Optic Radiation

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4
Q

Which order neurones are optic radiation and where do they terminate?

A

4th Order Neurones

They terminate in the primary visual cortex

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5
Q

What are the first, second and third order neurones in the visual pathway?

A

First Order – photo-receptors (rods and cones)
Second Order – bipolar cells
Third Order – retinal ganglion cells

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6
Q

What happens as the retinal ganglion cells enter the optic nerve, which improves the transmission of the signal?

A

They become myelinated

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7
Q

What percentage of retinal ganglion cell fibres crosses the midline at the optic chiasma?

A

53%

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8
Q

Describe the convergence and receptive field sizes of rods and cones.

A

Rods have high convergence and large receptive fields

Cones have low convergence and small receptive fields

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9
Q

Describe how the convergence of the rod system differs across different parts of the retina.

A

The rod system near that macula has lower convergence than in the peripheral retina

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10
Q

What is the benefit of having high convergence and a large receptive field?

A

High light sensitivity

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11
Q

What is the benefit of having low convergence and a small receptive field?

A

Fine visual acuity

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12
Q

Retinal ganglion cells can be described as on-centre or off-centre. What do these two terms mean?

A

On-centre – they are stimulated by light falling on the centre of the receptive field and inhibited by light falling on the edge of the receptive field
Off-centre – they are stimulated by light falling on the edge of the receptive field and inhibited by light falling on the centre
This is important in contrast sensitivity and enhanced edge detection

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13
Q

Where do the fibres that decussate at the optic chiasma originate?

A

The nasal part of the retina

These fibres are responsible for the temporal half of the visual field

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14
Q

What effect do lesions anterior to the optic chiasm have on vision?

A

Affects only ONE eye

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15
Q

What effect do lesions posterior to the optic chiasm have on vision?

A

Affects BOTH eyes
Right-sided lesion: left homonymous hemianopia
Left-sided lesions: right homonymous hemianopia

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16
Q

What is the effect of a lesion at the optic chiasm?

A

Bitemporal hemianopia

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17
Q

Which part of the brain does the upper division of the optic radiation travel through and which parts of the visual field is it responsible for?

A

Parietal Lobe

Responsible for the inferior visual quadrants

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18
Q

Which part of the brain does the lower division of the optic radiation travel through and what part of the visual field is it responsible for?

A

Temporal Lobe

Responsible for the superior visual quadrants

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19
Q

The lower division loops inferiorly and anteriorly before going posteriorly towards the primary visual cortex. What is this loop called?

A

Meyer’s Loop

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20
Q

What would be the consequence of a lesion in Meyer’s loop?

A

Superior homonymous quadrantopia

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21
Q

What would be the consequence of a lesion of the upper division of the optic radiation?

A

Inferior homonymous quadrantopia

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22
Q

What is homonymous hemianopia typically caused by?

A

Strokes and other cerebrovascular accidents

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23
Q

Where is the primary visual cortex located?

A

Along the Calcarine Fissure in the occipital lobe

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24
Q

Describe which parts of the primary visual cortex are responsible for the different fields of vision.

A

The macula has a disproportionate representation in the primary visual cortex
The left primary visual cortex is responsible for the right visual field from both eyes
The right primary visual cortex is responsible for the left visual field from both eyes
Visual cortex above the calcarine fissure is responsible for the inferior visual field
Visual cortex below the calcarine fissure is responsible for the superior visual field

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25
Q

How is it possible for the macula to be spared by a stroke in the primary visual cortex leading to homonymous hemianopia?

A

The area representing the macula in the primary visual cortex has adual blood supply (from both right and left posterior cerebral arteries) meaning that it is less vulnerable to ischaemia

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26
Q

What are the two pathways of the extrastriate cortex and what are they responsible for?

A

Dorsal Pathway – deals with motion detection

Ventral Pathway – handles detailed object recognition and face recognition

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27
Q

Describe what happens to the eyes in the light.

A

Iric circular muscle contracts
Constriction of pupillary aperture
Reduced rate of photopigment bleaching
Increased depth of field

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28
Q

Describe the pathway that is responsible for the consensual lightreflex.

A

Retinal ganglion cells from the retina send they axons back via the optic nerve
The fibres that are responsible for the pupillary reflex will get passed the optic chiasm and then leave the posterior 1/3 of the optic tract before it reaches the LGN
The axons then go to the pretectal nucleus in the dorsal brainstem
The afferent pathways from each eye then synapse on the Edinger-Westphal nuclei on both sides of the brainstem.
A parasympathetic nerve from the Edinger-Westphal nuclei to the ciliary ganglion forms the efferent pathway Short ciliary nerves travel from the ciliary ganglion to the pupillary sphincter
Summary:
Retinal Ganglion Cell –> Pretectal Nucleus –> Edinger-Westphal Nucleus –> Ciliary Ganglion –> Short Ciliary Nerves –> Sphincter Pupillae

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29
Q

What would the consequences be of a right afferent defect?

A

Light shone in right eye: no direct or consensual response

Light shone in left eye: direct and consensual response present

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30
Q

What would the consequences be of a right efferent defect?

A

Light shone in right eye: no direct response, consensual response present
Light shone in left eye: direct response, no consensual response

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31
Q

What does RAPD mean?

A

Relative Afferent Pupillary Defect
A partial pupillary response is still present despite damage to an eye and its pupillary reflex pathway – there is some degree of constriction

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32
Q

What test would you do to identify RAPD? What would you expect to see in a patient showing a RAPD?

A

Swinging Torch Test
When the light is shone on the good eye, there will be a direct and consensual response
When the light is then swung and shone at the bad eye, there will be a paradoxical dilation of the iris in the bad eye
This is because the constriction response elicited by the bad eye is weaker than the consensual response elicited by the good eyes

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33
Q

Define:

a. Duction
b. Version
c. Vergeance
d. Convergeance

A 
a. Duction 
Movement of one eye 
b. Version 
Simultaneous movement of both eyes 
c. Vergeance  
Simultaneous movement of both eyes in opposite directions
d. Convergeance  
Simultaneous adduction of both eyes when viewing a near object
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34
Q

What is the term for the elevation of one eye?

A

Supraduction

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35
Q

What is the term for the depression of both eyes?

A

Infraversion

36
Q

What is the technical term for right gaze?

A

Dextroversion

37
Q

What is the technical term for left gaze?

A

Levoversion

38
Q

What are the two types of eye movement and how are they different?

A

Saccade – short fast burst

Smooth Pursuit – sustained slow movement

39
Q

What reflex is used to assess visual acuity in preverbal children?

A

Optokinetic Nystagmus Reflex

It is a form of physiological nystagmus triggered by the presentation of a constantly moving grating pattern

40
Q

State which nerve innervates each of the extrinsic eye muscles.

A

Lateral Rectus = Abducens (CN VI)
Superior Oblique = Trochlear (CN IV)
Superior rectus and lid elevator (CN III sup)
Inferior rectus, medial rectus, inferior oblique and parasympathetic nerve for pupil constriction = CNIII inf

41
Q

Where do all the rectus muscles originate?

A

Common tendinous ring at the apex of the orbit

42
Q

Where do the rectus muscles insert?

A

Into the sclera anterior to the globe equator

43
Q

In what position would the eye have to be to get maximum elevation/depression due to:

a. Superior and Inferior Recti
b. Superior and Inferior Obliques

A

a. Superior and Inferior Recti
Abducted
b. Superior and Inferior Obliques
Adducted

44
Q

How would you test the extraocular muscles?

A

Isolate the muscle to be tested by maximising its action and minimising the action of the other muscles
E.g. to test the superior rectus, make the patient abduct and elevate their eye

45
Q

Describe and explain what you would see in a patient with 3rd nerve palsy.

A

Their affected eye would point down and out
This is because of the unopposed contraction of lateral rectus and superior oblique
Ptosis – because of the loss of innervation of levator palpebrae superioris
Pupil dilation – loss of parasympathetic innervation to the eye via CN III

46
Q

Describe and explain what you would see in a patient with 6thnerve palsy.

A

When asked the abduct the affected eye, they eye will stop around midline
This is because the lateral rectus isn’t functioning and can’t abduct the eye
This can lead to blurred vision

47
Q

What is the extra striate cortex?

A

Area around visual cortex within occipital lobe responsible for converting basic visual, orientation and positional info into complex info

48
Q

What are 6 extraocular eye muscles?

A 
Superior rectus 
Inferior rectus
Lateral (external) rectus
Medial rectus
Superior oblique
Inferior oblique
49
Q

Role of superior rectus

A

Moves eye up

50
Q

Role of inferior rectus

A

Moves eye down

51
Q

Role of lateral rectus

A

Moves eye towards temple

52
Q

Role of medial rectus

A

Moves eye towards middle of head

53
Q

Role of superior oblique

A

Moves eye diagonally downwards and in

54
Q

Anatomical features of superior oblique

A

Attaches high and laterally on eye
Passes under superior rectus
Travels through trochlea

55
Q

Role of inferior oblique

A

Moves eye diagonally up

56
Q

Anatomical features of inferior oblique

A

Attaches low on nasal side of eye

Passes over inferior rectus

57
Q

First order neurones in visual pathways

A

Rod and cone retinal photoreceptors

58
Q

Second order neurones in visual pathway

A

Retinal bipolar cells

59
Q

Third order neurones visual pathway

A

Retinal ganglion cells

60
Q

What is the receptive field of a neuron

A

Retinal space within which incoming light can alter the firing pattern of a neuron

61
Q

Difference in rod and cone system convergence

A

Rod system is greater than cone

62
Q

Difference in convergence between centre and periphery of eye

A

Higher peripheral convergence

63
Q

What does high convergence mean

A

Many photoreceptors per ganglion cell

64
Q

Differences between high and low convergence

A

High convergence means:
Larger receptive field
Broad visual acuity
High light sensitivity

65
Q

Difference in distribution of rod and cone receptors

A

In periphery more rod cells so better for processing fine movement

66
Q

Benefit of having on and off centre ganglion cells

A

Contrast sensitivity

Edge detection

67
Q

Common cause of bitemporal hemianopia

A

Pituitary gland tumour

68
Q

Location of primary visual cortex

A

Along culcarine sulcus in occipital lobe

69
Q

Other name for primary visual cortex

A

Striate cortex

70
Q

How is the cortex characterised

A

Distinct stripe of myelinated optic radiation projection into cortex

71
Q

Representation of visual field in cortex

A

Macula on lateral side of brain in very large area

Superior below culcarine fissure

72
Q

Route of visual ventral pathway

A

Primary visual cortex to inferiotemporal cortex

73
Q

Dorsal pathway visual cortex

A

Primary visual cortex to posterior parietal cortex

74
Q

Role of extrastriate cortex

A

These are areas around primary visual cortex in occipital lobe
Important in converting basic visual information to complex information

75
Q

Nerve supplying lid elevator

A

Superior branch of CN3

76
Q

Supply of superior rectus

A

Superior branch of CN3

77
Q

Supply of inferior and medial rectus

A

Inferior branch of CN3

78
Q

Supply of inferior oblique

A

Inferior branch of CN3

79
Q

Parasympathetic supply to constrict pupil

A

Inferior branch of CN3

80
Q

Supply of superior oblique

A

CN4

81
Q

Suplly of lateral rectus

A

CN6

82
Q

Nystagmus definition

A

Oscillatory eye movement

83
Q

Optokinetic nystagmus

A

Fast phase reset saccade

84
Q

Optokinetic nustagmus reflex use

A

Used in pre- verbal children to test their visual activity

85
Q

WhT is the Optokinetic nustagmus reflex

A

Observes presence of nystagmus movement in response to moving grating patterns

LCRS 2 (44 decks)

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