S4) The Retina and Central Visual Pathways Flashcards

1
Q

Identify the structures observed in the retina in a cross-section of the eyeball

A
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2
Q

What are rod cells and what do they do?

A

Rod cells are photoreceptor cells in the retina which function in low intensity light and are responsible for black and white vision

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3
Q

What are cone cells and what do they do?

A

Cone cells are photoreceptor cells in the retina which function in high intensity light and are responsible for high acuity vision (detects colours)

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4
Q

What are bipolar cells and what do they do?

A

Bipolar cells are cells which exist between photoreceptors in the retina and act indirectly/directly to transmit signals from the photoreceptors to the ganglion cells

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5
Q

What are horizontal cells and what do they do?

A

- Horizontal cells are the laterally interconnecting neurons which help integrate and regulate the input from multiple photoreceptor cells

  • They also allow the eyes to adjust to see well in both bright & dim light conditions
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6
Q

What are amacrine cells and what do they do?

A

Amacrine cells are inhibitory neurons and project their dendrites to the inner plexiform layer to interact with retinal ganglion cells and/or bipolar cells

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7
Q

What are ganglion cells and what do they do?

A

A retinal ganglion cell is a type of neuron in the retina which receives visual information from photoreceptors via bipolar cells and amacrine cells

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8
Q

Identify the seven structures observed in a fundoscopy of the eye

A
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9
Q

Illustrate the layout of the visual pathway

A
  • Temporal fibres run ipsilateral
  • Nasal fibres decussate at the optic chiasm
  • Optic tract runs to the lateral geniculate nucleus
  • Optic radiations split into superior and inferior and runs to the primary visual cortex
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10
Q

Briefly, describe the layout of the visual fields

A
  • Nasal fibres are responsible for our temporal field of vision
  • Temporal fibres are responsible for our nasal field of vision

Lesions at any point in the pathway will correspond to a pattern of visual loss

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11
Q

How are visual field defects named?

A

These are named based on the area of visual loss rather than the site of the lesion

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12
Q

Describe the pattern of visual field loss at the following locations:

  • Before the optic chiasm
  • At/after the optic chiasm
  • After the optic chiasm
A
  • Before the optic chiasm: signs are unilateral and ipsilateral
  • At/after the optic chiasm: signs are bilateral
  • After the optic chiasm: signs will be bilateral and contralateral
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13
Q

What is the general cause of monocular blindness?

A

Monocular blindness is caused by a lesion of the optic nerve (right)

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14
Q

Identify some of the underlying pathological causes of monocular blindness in children and adults

A
  • Optic nerve glioma or retinoblastoma (children)
  • Optic sheath meningiomas (middle aged)
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15
Q

What is the general cause of bitemporal hemianopia?

A

- Bitemporal hemianopia is caused by a lesion at the optic chiasm

  • It affects both nasal fibres, and thus, both temporal fields lost
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16
Q

What is the general cause of left homonymous hemianopia?

A
  • Left homonymous hemianopia is caused by a lesion of the right optic tract
  • It affects the right temporal and left nasal fibres
17
Q

What is the general cause of right homonymous hemianopia?

A
  • Right homonymous hemianopia is caused by a lesion of the left optic tract
  • It affects the left temporal and right nasal fibres
18
Q

Identify some of the underlying pathological causes of right/left homonomous hemianopia

A
  • Vascular causes (stroke – common)
  • Neoplasia
  • Trauma
19
Q

What is a quadrantanopia?

A

A quadrantanopia is an anopia affecting a quarter of the field of vision, associated with a lesion of an optic radiation

20
Q

Localise a quadrantopia observed in the following visual fields:

  • Left field
  • Right field
  • Superior field
  • Inferior field
A
  • Left field → Right hemisphere
  • Right field → Left hemisphere
  • Superior field → Inferior radiations
  • Inferior field → Superior radiations
21
Q

The occipital lobe has dual blood supply.

Identify these arteries

A
  • Posterior cerebral artery
  • Middle cerebral artery (occipital pole)
22
Q

In four steps, explain the concept of macular sparing after a stroke

A

⇒ Stroke can affect the posterior cerebral artery

⇒ Most of occipital lobe will be lost

Middle cerebral artery supplies the occipital pole (represents the macula)

Macular function (central vision) will be spared

23
Q

In four steps, describe the nervous pathways involved in the light reflex

A

⇒ Light stimulates the afferent nerve in the pathway (CN II)

⇒ Afferent nerve synapses in pretectal area

⇒ Gives rise to neurones supplying Edinger Westphal nuclei bilaterally

⇒ Both CN III are stimulated to cause direct and consensual pupillary constriction (parasympathetic fibres)

24
Q

Describe the three aspects of the accommodation reflex as well as the structures involved

A
  • Convergence (medial rectus)
  • Pupillary constriction (constrictor pupillae)
  • Convexity of the lens to increase refractive power (ciliary muscle)
25
Q

Briefly, explain how the cerebral cortex is involved in the accommodation reflex (image analysis)

A

The reflex follows the visual pathway via the lateral geniculate nucleus to the visual cortex