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BRS Y2 > Pathways of the Visual System > Flashcards

Pathways of the Visual System Flashcards

1
Q

Describe the order of the visual pathway

A 
Eye
Optic nerve
Optic chiasm
Optic tract
Lateral geniculate nucleus
Optic radiation
Primary visual cortex
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2
Q

What happens to fibres at the optic chiasm?

A

50% of them cross over

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3
Q

What synapses at the lateral geniculate nucleus?

A

The ganglion nerve fibres

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4
Q

Where is the primary visual cortex found?

A

Within the occipital lobe

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5
Q

In the retina what are the 1st order neurons?

A

Rod and cone retinal photoreceptors

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6
Q

In the retina what are the 2nd order neurons?

A

Retinal bipolar cells

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7
Q

In the retina what are the 3rd order neurons?

A

Retinal ganglion cells

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8
Q

What will lesions anterior to the optic chiasm affect?

A

The visual field of one eye

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9
Q

What will lesions posterior to the optic chiasm affect?

A

The visual field of both eyes

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10
Q

What visual field are crossed fibres responsible for?

A

The temporal visual field

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11
Q

What visual field are uncrossed fibres responsible for?

A

The nasal visual field

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12
Q

Where do crossed fibres originate from?

A

The nasal retina

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13
Q

Where do uncrossed fibres originate from?

A

The temporal retina

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14
Q

What will a lesion at the optic chiasm affect?

A

Both visual field, it will cause a bitemporal hemianopia

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15
Q

What is a homonymous hemianopia?

A

The patient sees only the left or right visual field in BOTH eyes

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16
Q

What is a bitemporal hemianopia?

A

Loss of peripheral visual field in BOTH eyes

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17
Q

What is a quadrantanopia?

A

Loss of visual field in one quadrant of both eyes

18
Q

What is macular sparring?

A

When there is loss of visual field eg left visual field of both eyes BUT the very centre of the visual field is preserved

19
Q

What is the most common cause of bitemporal hemianopia?

A

Compression of the optic chiasm due to pituitary enlargement

20
Q

What is the most common cause of homonymous hemianopia?

A

Stroke/ cerebrovascular accident

21
Q

When does homonymous hemianopia with macular sparring occour?

A

If there is damage to the primary visual cortex eg due to stroke

22
Q

What does the pupil regulate?

A

How much light is let into the eye

23
Q

What happens to the pupil when its exposed to light?

A

It constricts

24
Q

What does constriction of the pupil do?

A

Decreases glare
Increases depth of field
Reduces bleaching of photo pigments

25
Q

What nerve carries out constriction of the pupil?

A

Parasympathetic nerve (CN III)

26
Q

What muscles contract to cause pupil constriction?

A

Circular muscles

27
Q

What happens to the pupil in the dark?

A

It dilates

28
Q

What does dilation of the pupil achieve?

A

Allows increased sensitivity to light by allowing more light into the eye

29
Q

What nerve carries out dilation of the pupil?

A

Sympathetic nerve

30
Q

What muscles contract to allow dilation of the pupil?

A

Radial muscles

31
Q

Describe the afferent pathway starting at rod and cone photoreceptors

A

Rod and cone photoreceptors synapse on bipolar cells
These synapse on retinal ganglion cells
Ganglion cells exit at posterior third of optic tract before entering lateral geniculate nucleus
Synapses on Edinger-Westphal nuclei on both sides of the brainstem

32
Q

Describe the efferent pathway starting at the Edinger Westphal nucleus

A

Edinger Westphal nucleus goes to oculomotor nerve efferent
Synapses at the ciliary ganglion
Short posterior ciliary nerve goes to pupillary sphincter

33
Q

What are the 2 pupillary reflexes?

A

Direct and consensual

A normal reflex will illicit both

34
Q

What is the direct pupillary reflex?

A

Constriction of the pupil in the eye that is stimulated by light

35
Q

What is the consensual pupillary reflex?

A

Constriction of the pupil in the other eye (not the one that is stimulated by light)

36
Q

If there is a right afferent defect, how will the pupillary reflex be affected?

A

No constriction in either pupil when light is shone in the right eye
Constriction in both pupils when light is shone in the left eye

37
Q

If there is a right efferent defect, how will the pupillary reflex be affected?

A

No constriction in the right pupil when either eye is stimulated
Constriction in the left eye when either pupil is stimulated

38
Q

If there is a unilateral afferent defect, how will the pupillary reflex be affected?

A

Whichever eye is damaged will not constrict when it is stimulated, it will constrict when the undamaged is stimulated
The undamaged eye will always constrict despite which eye is stimulated

39
Q

If there is a unilateral efferent defect, how will the pupillary reflex be affected?

A

Whichever eye is damaged will not constrict when either eye is stimulated
The undamaged eye will constrict when either eye is stimulated

40
Q

Which test is used to check the afferent and efferent eye pathways?

A

The swinging torch test

BRS Y2 (85 decks)

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