L5 - Visual Pathway Flashcards Preview

Clinical neuroscience > L5 - Visual Pathway > Flashcards

Flashcards in L5 - Visual Pathway Deck (28)
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1
Q

3 layers of the eye

A

Sclera
Uvea - pigmented vascular layer
Retina - neural layer

2
Q

Sclera

A

Tough and fibrous

Continuous with the dural sheath of the optic nerve

3
Q

Uvea

A

Choroid

Ciliary body and iris

4
Q

Retinal layers

A

Retinal pigment epithelium:

  • absorbs light therefore prevents light from bouncing around in the eyeball causing flare
  • anchor photoreceptors - converts light into action potential

Neural layer:

Photoreceptors

Bipolar cells:

  • first order sensory neurones that receive input from photoreceptors
  • connect photoreceptors to axons of ganglion cells

Ganglion cells:

  • receives input from bipolar cells
  • axons of the ganglion cells form the optic nerve
5
Q

Horizontal cells

A

Connect bipolar cells which assists with enhancing edges via lateral inhibition

6
Q

Amaurosis fugax

A
  • Occlusion symptoms occurs of the central retinal artery (branch of the ophthalmic artery)
  • curtain coming down obscuring vision
  • symptom of stroke
7
Q

How to visualise retinal layers

A

Optical coherence tomography (OCT)

8
Q

Blind spot

A

Optic disc

9
Q

What can fundoscopy detect?

A
  • Retinopathies - due to hypertension or diabetes
  • Vascular occlusion - amourosis fugax
  • macular degeneration
  • optic disc - papilloedema
10
Q

Fovea

A

Small distance between the nerve fibre layer and the retinal pigment layer therefore high acuity vision

11
Q

Nasal and temporal fibres at the optic chiasm

A

Nasal fibres decussate

Temporal fibres remain ipsilateral

12
Q

Lateral geniculate nucleus

A

Receive optic tracts

13
Q

Superior optic radiations

A
  • continuation of the nasal and temporal superior quadrant fibres
  • Baum’s loop
  • Travel via parietal lobe
  • run to the primary visual cortex
14
Q

Inferior optic radiations

A
  • continuations of the inferior nasal and temporal quadrant fibres
  • Meyer’s loop
  • travel via the temporal lobe
  • run to the primary visual cortex
15
Q

Visual field

A

Area that is visible by each eye

16
Q

Binocular vision

A
  • Area of visual field overlap between both eyes

- Allows depth perception

17
Q

Temporal visual field

A

Temporal visual field detected by the nasal retinal fibres

As light travels in straight lines

18
Q

How are visual field defects named

A

By the area of visual field loss

19
Q

Optic nerve lesion

A
  • both temporal and nasal fibres on the ipsilateral side are affected as has not decussated
  • therefore both the nasal and temporal visual fields affected
  • monocular blindness
20
Q

Optic chiasm lesion

A
  • left and right nasal optic fibres are affected
  • therefore temporal visual field loss in both eyes
  • bitemporal hemianopia
  • commonly caused by pituitary tumours and aneurysms that can compress the chiasm
21
Q

Left optic tract lesion

A
  • left temporal fibres (ipsilateral) and right nasal fibres (contralateral) affected
  • therefore left nasal visual field and right temporal visual field affected
  • homonomous hemianopia

-

22
Q

Superior radiations

A

Inferior quadrant visual field detected by the superior optic radiations

  • project into parietal lobe
23
Q

Quadrantanopias - right superior optic radiation

A
  • Lesion affecting the superior right temporal fibre and superior left nasal fibre
  • Therefore the inferior right nasal visual field (ipsilateral) and inferior left temporal visual field (contralateral) is affected
  • Homonomous inferior quadrantanopia
24
Q

Lesion of the right inferior optic radiation (temporal lobe)

A
  • lesion of the right inferior temporal fibre (ipsilateral) and left inferior nasal fibre (contralateral)
  • therefore the right superior nasal visual field affected and left superior temporal visual field affected
  • homonomous superior quadrantanopia
25
Q

Lesion in right superior and inferior radiations

A
  • due to e.g. stroke affecting the parietal and temporal lobe
  • superior and inferior right temporal fibres affected and superior and inferior left nasal fibres affected
  • therefore superior and inferior right nasal visual field affected and superior and inferior left temporal visual field affected
  • homonomous hemianopia
26
Q

Macular sparing

A

Occipital lobe has a dual blood supply:

  • posterior cerebral artery
  • middle cerebral artery (occipital pole)

In a stroke affecting the posterior cerebral artery most of the occipital lobe will be lost but the middle cerebral artery supplies the occipital pole which represents the macula

Therefore macula vision i.e. central vision will be spared

27
Q

Pupillary light reflex

A
  1. Light stimulates the afferent optic nerve
  2. It gives off a branch that synapses in the pretectal area onto the interneurone
  3. The interneurone travels to the brain stem which supplies the Edinger Westphal nucleus
  4. The preganglionic fibres run with the occulomotor nerve and synapses in the ciliary body.
  5. Postganglionic fibres run with the trigeminal nerve to the constrictor pupillae and ciliary muscle
  6. Both occulomotor nerves are stimulated to cause direct and consensual pupillary constriction.
28
Q

Accommodation reflex

A
  • light from near objects refract more exceeding the limit of the lens

Therefore the accommodation reflex causes:

  • convergence
  • pupillary constriction
  • lens becomes more convex - increases refractive power via the ciliary muscle
  1. Reflex follows the lateral geniculate nucleus to the visual cortex for image analysis
  2. Fibres sent from the primary visual cortex to the midbrain to the EDW nucleus and occulomotor nerve
  3. Stimulation causes parasympathetic pupil constriction and ciliary muscle contraction for lens thickening and medial rectus contraction to adduct eye inwards towards the midline