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Year 2 Neuro > 12 - Neurology of the visual system > Flashcards

12 - Neurology of the visual system 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

What is the visual pathway?

Where does it transmit to in the brain - anatomically, where is this?

A

the neurological pathway, where by vision is converted to neurological impulses, to be transmitted from the eye to the visual cortex, the posterior part of the brain

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3
Q

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

A

Lateral Geniculate Nucleus

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4
Q

Where is the lateral geniculate nucleus found?

A

Thalamus

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5
Q

What are the fibres leaving the lateral geniculate nucleus called?

A

Optic Radiation

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6
Q

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

A

4th Order Neurones

They terminate in the primary visual cortex

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7
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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8
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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9
Q

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

A

Around half (53%)

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10
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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11
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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12
Q

What is the benefit of having high convergence and a large receptive field?
Which type of photoreceptor does this relate to?
What is the disadvantage of these types of photoreceptors?

A

High light sensitivity - reacting to rods

BUT have a coarse visual acuity

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13
Q

What is the benefit of having low convergence and a small receptive field?
Which type of photoreceptor does this relate to?
What is the disadvantage of these types of photoreceptors?

A

Fine visual acuity - relating to cones

BUT have low light sensitivity

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14
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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15
Q

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

Where do fibres that don’t decussate at the optic chiasm originate?

A

The nasal part of the retina
These fibres are responsible for the temporal half of the visual field

Originate from temporal retina.
They are responsible for nasal visual field.

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16
Q

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

A

Affects only ONE eye

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17
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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18
Q

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

A

Bitemporal hemianopia

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19
Q

What is a bitemporal hemianopia typically caused by?

A

enlargement of the pituitary gland tumour

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20
Q

What is homonymous hemianopia typically caused by?

A

Strokes and other cerebrovascular accidents

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21
Q

Give another name for the primary visual cortex and state where it is located?

A

Striate cortex

Located along the Calcarine Fissure in the occipital lobe

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22
Q

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

A
  • 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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23
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 so, it is less vulnerable to ischaemia

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24
Q

What is the extrastriate cortex?

A

The Primary Visual Cortex (striate cortex) relays visual information to the Extra-striate Cortex, a region adjacent to the Primary Visual Cortex, for further higher visual processing.

  • Area around PVC within the Occipital Lobe
  • Converts basic visual information, orientation and position into complex information
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25
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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26
Q

Describe the dorsal pathway, what is it responsible for and what damage to to will cause

A
  • Primary Visual Cortex -> Posterior Parietal Cortex
  • function in Motion Detection and Visually-Guided Action
  • Damage results in Motion Blindness
27
Q

Describe the ventral pathway, what is it responsible for and what damage to to will cause

A
  • Primary Visual Cortex -> Inferiotemporal Cortex
  • function in Object Representation, Face Recognition and detailed fine central and colour vision
  • Damage may result in 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 what happens to the eyes in the dark.

A
  • pupil dilation due to radial muscle contraction

- increased light sensitivity

30
Q

Describe the Afferent pathway for the pupillary reflex

A

• Photoreceptors synapse on Bipolar Cells, which synapse on Retinal Ganglion Cells - they send axons via the optic nerve
• Pupil-specific ganglion cells exit at posterior third of optic tract before entering the LGN
(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)
• Synpases at Brain Stem (Pretectal Nucleus)
• Afferent (incoming) pathway from each eye synapses on Edinger-Westphal Nuclei on both sides in the brainstem

31
Q

Describe the efferent pathway for the pupillary reflex

A

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

32
Q

Summarise the pathway that is responsible for the consensual light reflex (afferent and efferent)

A

Retinal Ganglion Cell -> Pretectal Nucleus -> Edinger-Westphal Nucleus -> Ciliary Ganglion -> Short Ciliary Nerves -> Sphincter Pupillae

33
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

34
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

35
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

36
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 eye

37
Q

Define duction

A

Movement of one eye

38
Q

Define version

A

Simultaneous movement of both eyes

39
Q

define vergeance

A

Simultaneous movement of both eyes in opposite directions

40
Q

define convergeance

A

Simultaneous adduction of both eyes when viewing a near object

41
Q

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

A

Saccade – short fast burst

Smooth Pursuit – sustained slow movement

42
Q

Name the 6 extra ocular muscles

Where do they originate from?

A 
4 rectus muscles:
- Superior rectus
- Inferior rectus
- Lateral rectus
- Medial rectus
2 oblique muscles:
- superior oblique
- inferior oblique

5 of the 6 muscles come out of a cone from the back of the orbit. The inferior oblique comes in nasally.

43
Q

What is the term for the elevation of one eye?

A

Supraduction

44
Q

What is the term for the depression of both eyes?

A

Infraversion

45
Q

Where are the vertical rectus muscle attached? How do they move the eye?

A

attach anterior to the globe equator, and pull backwards and nasally

Superior rectus
Attached to the eye at 12 o’clock, moves the eye up.
Inferior rectus
Attached to the eye at 6 o’clock, moves the eye down.

46
Q

Where is the lateral rectus attached? How does it move the eye?

A

It attaches on the temporal side of the eye

It moves the eye toward the outside of the head (toward the temple)

47
Q

Where is the medial rectus attached? How does it move the eye?

A

It attaches on the nasal side of the eye

It moves the eye toward the middle of the heard (towards the nose)

48
Q

Describe the attachment and the path of the superior oblique muscle
How does it move the eye?

A
  • Attached high on the temporal side of the eye.
  • Passes under the Superior Rectus.
  • Moves the eye in a diagonal pattern – down and in.
  • Travels through the trochlea
49
Q

Describe the attachment and the path of the inferior oblique muscle
How does it move the eye?

A
  • Attached low on the nasal side of the eye
  • Passes over the Inferior Rectus
  • Moves the eye in a diagonal pattern – up and out
50
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)

51
Q

Where do all the rectus muscles originate?

A

Common tendinous ring at the apex of the orbit

52
Q

Where do the rectus muscles insert?

A

Into the sclera anterior to the globe equator

53
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
54
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

55
Q

Define supraversion

A

The elevation of both eyes

namely simultaneous right and left eye supraduction.

56
Q

Define infraversion

A

Depression of both eyes

namely simultaneous right and left eye infraduction.

57
Q

What is dextroversion?

A

right gaze

involves simultaneous right eye abduction, and left eye adduction

58
Q

What is levoversion?

A

left gaze

involves simultaneous left eye abduction, and right eye adduction

59
Q

What is torsion?

A

rotation of eye around the anterior-posterior axis of the eye

60
Q

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

A
  • affected eye pointing down and out
    due to the unopposed contraction of lateral rectus and superior oblique
  • Ptosis – loss of innervation of levator palpebrae superioris
61
Q

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

A
  • deficit in abduction in the affected eye
    This is made apparent when the patient is asked to abduct the affected eye, eye stops around the midline
    This is because the lateral rectus isn’t functioning and can’t abduct the eye
  • affected eye deviates inwards (unable to abduct)
  • Double vision worsen on gazing to the side of affected eye
62
Q

What is Optokinetic Nystagmus?

A

Form of physiological nystagmus (oscillatory eye movement), triggered by the presentation of a constantly moving grating pattern.

Smooth Pursuit + Fast Phase Reset Saccade

63
Q

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

  • may want to reword
A

Optokinetic Nystagmus Reflex is useful in testing visual acuity in pre-verbal children by observing the presence of nystagmus movement in response to moving grating patterns of various spatial frequencies

Presence of Optokinetic Nystagmus in response to moving grating signifies that the subject has sufficient visual acuity to perceive the grating pattern

Year 2 Neuro (16 decks)

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