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Neuro OBG > Visual Pathways and Control of Eye Movements > Flashcards

Visual Pathways and Control of Eye Movements Flashcards

1
Q

What are the main landmarks of the visual pathway?

A 
Eye 
Optic Nerve  
Optic Chiasm 
Optic Tract  
Lateral Geniculate Nucleus  
Optic Radiation 
Primary Visual Cortex (Striate Cortex)
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2
Q

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

A

Lateral Geniculate Nucleus

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3
Q

Where is the lateral geniculate nucleus found?

A

Thalamus

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4
Q

What are the fibres leaving the lateral geniculate nucleus called?

A

Optic Radiation

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5
Q

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

A

4th Order Neurones

They terminate in the primary visual cortex

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6
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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7
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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8
Q

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

A

53%

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9
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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10
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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11
Q

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

A

High light sensitivity

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12
Q

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

A

Fine visual acuity

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13
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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14
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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15
Q

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

A

Affects only ONE eye

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16
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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17
Q

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

A

Bitemporal hemianopia

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18
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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19
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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20
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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21
Q

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

A

Superior homonymous quadrantopia

22
Q

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

A

Inferior homonymous quadrantopia

23
Q

What is homonymous hemianopia typically caused by?

A

Strokes and other cerebrovascular accidents

24
Q

Where is the primary visual cortex located?

A

Along the Calcarine Fissure in the occipital lobe

25
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

26
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 a dual blood supply (from both right and left posterior cerebral arteries) meaning that it is less vulnerable to ischaemia

27
Q

What are the two (visual) pathways of the extrastriate cortex and what are they responsible for? if damaged what occurs

A

Dorsal Pathway (primary vis cortex–>posterior parietal cortex)– deals with motion detection- damage leads to motion blindness

Ventral Pathway (primary vis cortex–> inferotemporal cortex)– handles detailed object recognition and face recognition- fine central vision/colour vision- damage leads to cerebral achromatopsia

28
Q

Describe what happens to the eyes in the light.

A

Iris circular muscle contracts

Constriction of pupillary aperture

Reduced rate of photopigment bleaching

Increased depth of field

29
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

30
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

31
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

32
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

33
Q

What test would you do to identify RAPD? What would you expect to see in a patient showing a RAPD?
(Relative Afferent Pupillary Defect )

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 eye

34
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

35
Q

What is the term for the elevation of one eye?

A

Supraduction

36
Q

What is the term for the depression of both eyes?

A

Infraversion

37
Q

What is the technical term for right gaze?

A

Dextroversion

38
Q

What is the technical term for left gaze?

A

Levoversion

39
Q

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

A

Saccade – short fast burst

Smooth Pursuit – sustained slow movement

40
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

  • smooth pursuit + fast paced reset saccade
  • shows ability to perceive motion
41
Q

State which nerve innervates each of the extrinsic eye muscles.

A

Lateral Rectus = Abducens (CN VI)
Superior Oblique = Trochlear (CN IV)
Medial Rectus, Superior Rectus, Inferior Oblique, Inferior Rectus and Levator Palpebrae Superioris = Oculomotor (CN III)

42
Q

Where do all the rectus muscles originate?

A

Common tendinous ring at the apex of the orbit

43
Q

Where do the rectus muscles insert?

A

Into the sclera anterior to the globe equator

44
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

45
Q

Explain why this (why you adduct the eye to test oblique muscles) is with respect to the anterior-posterior axis of the eye.

A

The anterior-posterior axis of the eye is aligned with the axis of the vertical recti when the eye is abducted

If the eye is adducted, the axes are not aligned and contraction of the vertical recti would cause torsion

46
Q

Where do oblique muscles attach to the eye?

A

Into the sclera posterior to the globe equator

47
Q

The oculomotor nerve has two branches. State what each of these branches innervates.

A

Superior Oculomotor Nerve
 Superior Rectus
 Levator Palpebrae Superioris

Inferior Oculomotor Nerve  
 Inferior Rectus 
 Medial Rectus 
 Inferior Oblique 
 Parasympathetic nerve that causes pupil constriction
48
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

49
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

50
Q

Describe and explain what you would see in a patient with 6th nerve 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

51
Q

What structure in the brainstem acts as a synchronising link between the eyes, allowing paired eye movements?

A

Medial Longitudinal Fasciculus

52
Q

What can damage to the MLF cause?

A

Internuclear Opthalmoplegia

E.g. right abduction wont be accompanied by left adduction

Could be accompanied by nystagmus on right gaze

Neuro OBG (20 decks)

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