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ESA 5 - Nervous System > The Retina and Central Visual Pathways > Flashcards

The Retina and Central Visual Pathways Flashcards

1
Q

What are the important layers of the retina?

A
  • Choroid
  • Pigemented layer
  • Neural layer
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2
Q

What cells are contained within the neural layer of the retina?

A
  • Photoreceptor cells
  • Bipolar cells
  • Horizontal cells
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3
Q

What does the pigemented layer of the retina contain?

A

Melanin

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4
Q

What are the functions of the pigemented layer of the retina?

A
  • Reduces refraction of light
  • Acts as an anchor for photoreceptor cells
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5
Q

Why is it important that the pigmented layer of the retina reduces the refraction of light?

A

Prevents the light from being too bright

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6
Q

What are the types of photoreceptor cells?

A
  • Rod cells
  • Cone cells
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7
Q

What are rod cells good for?

A
  • Black and white
  • Low levels of light
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8
Q

What are cone cells good for?

A
  • Colour vision
  • Higher acuity vision
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9
Q

What is the function of horizontal cells?

A

They are inhibitory cells that are employed so you don’t get too many conflicting messages from photoreceptors

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10
Q

Which part of the retina is responsible for central vision?

A

The macula lutea

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11
Q

What is found within the macula?

A

The fovea centralis

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12
Q

What is significant about the fovea centralis?

A

It has the highest concentration of cone cells, and therefore allows you to see details when looking straight ahead

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13
Q

How can the retina be visualised?

A

Fundoscopy

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14
Q

What can fundoscopies be useful to visualise?

A
  • Retinopathies
  • Vascular occlusions
  • Macula
  • Optic disc
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15
Q

What retinopathy can be caused by vascular occlusions?

A

Amaurosis fungax

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16
Q

What is amaurosis fugax?

A

A usually transient condition characterised by a ‘curtain coming down’ over vision

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17
Q

What optic disc pathology can be seen on fundoscopy?

A

Swelling of the optic disc, called papilloedema

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18
Q

What is papillodema a sign of?

A

Raised ICP

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19
Q

Other than fundoscopy, what investigations can be done on the eye?

A

Optical coherence tomography

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20
Q

Which fibres of the optic nerve run ipsilaterally?

A

The temporal fibres

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21
Q

Which fibres of the optic nerve decussate at the optic chiasm?

A

The nasal fibres

22
Q

Where do the optic tracts run?

A

From the optic chiasm to the lateral geniculate nucleus

23
Q

What happens to the optic radiations?

A

They split into superior and inferior portions, and run into the primary visual cortex

24
Q

What field of vision are the nasal fibres responsible for?

A

The temporal

25
Q

What field of vision are the temporal fibres responsible for?

A

The nasal

26
Q

What is the clinical relevance of knowing the pathway of the optic nerve?

A

Becasue lesions at any point in the pathway will correspond to a pattern of visual loss, and so the pattern of loss can localise the lesion

27
Q

What are visual fields named based on?

A

The area of visual loss, not the site of the lesion

28
Q

What does a visual loss that is unilateral and ipsilateral suggest?

A

The damage has occured before the optic chiasm

29
Q

What does a bilateral visual loss suggest?

A

The damage occurs at or after the optic chiasm

30
Q

What does a visual loss that is bilateral and contralateral suggest?

A

The damage occurs after the optic chiasm

31
Q

What is monocular blindness?

A

Blindness in one eye

32
Q

What is monocular blindness caused by?

A

A lesion of the optic nerve

33
Q

Give two examples of things that might cause a lesion of the optic nerve in children

A
  • Optic nerve glioma
  • Retinoblastoma
34
Q

Give an example of a condition that can cause an optic nerve lesion in adults

A

Meningiomas

35
Q

What is bitemporal hemianopia?

A

A loss of vision in both temporal fields, also known as tunnel vision

36
Q

What causes bitemporal hemianopia?

A

A lesion at the optic chiasm, therefore affecting both nasal fibres and so loss of both temporal fields

37
Q

What can cause a lesion at the optic chiasm?

A

Pathology of the pituitary gland or anterior communicating artery

38
Q

What causes a left homonomous hemianopia?

A

A loss of the right temporal and left nasal fibres due to a lesion of the right optic tract

39
Q

What can cause a lesion of the optic tract?

A
  • Stroke
  • Neoplasia
  • Trauma
40
Q

What causes a right homonomous hemianopia?

A

Loss of the left temporal and right nasal fibres, caused by a lesion of the left optic tract

41
Q

What is the blood supply of the occipital lobe?

A
  • Posterior cerebral artery
  • Occipital part of the middle cerebral artery

Has a dual blood supply

42
Q

What happens in a stroke affecting the posterior cerebral artery?

A

Most of the occipital lobe will be lost, however the middle cerebral artery supplies the occipital pole, which represents the macula. Therefore, macula function will be spared

43
Q

Describe the pathway of the light reflex

A
  1. The light stimulates the afferent nerve - CN II
  2. The nerve synpases in the pretectal area, which gives rise to neurones supplying the Edinger-Westphal nuclei bilaterally
  3. The pre-ganglionic parasympathetic fibres and then post-ganglionic parasympathetic fibres of both oculomotor nerves are stimulated to cause direct and consenual pupillary constriction
44
Q

What is the accomodation reflex required for?

A

Near vision

45
Q

What aspects does the accommodation reflex consist of?

A
  • Convergence
  • Pupillary constriction
  • Change in convexity of the lens to increase its refractive power
46
Q

What muscle is responsible for convergence in the accomodation reflex?

A

Medial rectus

47
Q

What muscle is responsible for pupillary constriction in the accomodation reflex?

A

Constrictor pupillae

48
Q

What muscle is responsible for the change in convexity of the lens to increase the refractive power in the accomodation reflex?

A

The ciliary muscle

49
Q

Why must the cerebral cortex be involved in the accomodation reflex?

A

Because it is related to image analysis

50
Q

What is the result of the accomodation reflex involving the cerebral cortex on the pathway it must take?

A

The visual pathway goes via the lateral geniculate nucleus to the visual cortex

51
Q

Where does the accomodation reflex pathway go from the visual cortex?

A

It is common with the light reflex pathway, via the Edinger-Westphal nucleus

ESA 5 - Nervous System (18 decks)

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