4.1 Visual pathway

Question 1

functions of pigmented layer

Answer 1

main absorption of light
contains melanin to modulate amount of light received

anchors photoreceptor cell, as they’re embedded in pigmented epithelium

Question 2

functions of horizontal cells

Answer 2

inhibitory interneurones which do lateral inhibition (no signals from photoreceptors either side of the photoreceptor detecting impulse), prevents XS neural impulses to brain

so increases contrast and narrows light signals

Question 3

functions of bipolar cells

Answer 3

connect a few photoreceptor cells to bipolar neurone to axons of retinal ganglion cells to optic nerve

Question 4

amaurosis fugal

Answer 4

occlusion of (branch of) central retinal artery/vein or ICA

sudden transient loss of vision due to hypoxia of retina

‘curtain down over vision’

symptom of stroke

Question 5

papilloedema

Answer 5

swollen optic disc secondary to raised ICP, causing optic nerve compression

Question 6

retinal detachment: pathophysiology and symptoms

Answer 6

separation of photoreceptors from pigmented layer, fluid can enter space

sudden blurring/loss of vision
seeing stars

Question 7

benefits of fovea structure

Answer 7

ganglion cell axons are splayed, creating a dip

less distance for light to penetrate to reach cones = impulses easier, central vision

high density of cones = high resolution vision

Question 8

which lobe do superior optic radiations pass through?

Answer 8

parietal

Question 9

which lobe do inferior optic radiations pass through?

Answer 9

temporal

Question 10

how do we have binocular vision?

Answer 10

L+R visual fields overlap

Question 11

which retinal fibres are responsible for central vision?

Answer 11

temporal (via nasal visual fields)

Question 12

pattern of vision loss in CN2 lesion

Answer 12

ipsilateral temporal and nasal retinal fibres affected

so lose ipsilateral nasal and temporal visual fields

=MONOCULAR BLINDNESS

Question 13

pattern of vision loss in optic chasm lesion

Answer 13

ipsilateral and contralateral nasal retinal fibres affected

so both temporal visual fields lost

=BITEMPORAL HEMIANOPIA (tunnel vision)

Question 14

causes of bitemporal hemianopia

Answer 14

pituitary adenoma
anterior communicating artery aneurysm

Question 15

pattern of vision loss in optic tract lesion

Answer 15

ipsilateral temporal fibres affected, and contralateral nasal fibres

so loss of ipsilateral nasal visual field, and contralateral temporal visual field

=HOMONOMOUS HEMIANOPIA

Question 16

which optic radiations are responsible for inferior quadrant field of vision? via projection to which lobe?

Answer 16

superior

parietal lobe

Question 17

pattern of vision loss for right superior optic radiation lesion

Answer 17

ipsilateral superior temporal fibre + contralateral superior nasal fibre affected

so ipsilateral inferior nasal field and contralateral inferior temporal fields lost

= HOMONOMOUS INFERIOR QUADRANTANOPIA

Question 18

how to distinguish between a lesion affecting superior and inferior optic radiations e.g. stroke, vs optic tract lesion

Answer 18

history and symptoms

Question 19

is there cortical involvement in pupillary reflex (1), and accommodation reflex (2)?

Answer 19

1. no
2. yes due to image processing and analysis

Question 20

the optic nerve synapses on pre tectal nucleus, where is this?

Answer 20

tectum of midbrain

Question 21

accommodation reflex pathway

Answer 21

light stimulates afferent optic nerve

synapses in lateral geniculate nucleus

impulses to midbrain from PVC

then to 2 nuclei: edinger Westphal (parasympathetic fibres for sphincter pupillae and ciliary muscle contraction) and CN3 (contraction of medial rectus)

Question 22

what’s meant by the medial longitudinal fasciclus?

Answer 22

loads of connections between nuclei of CN3,4,6,8 and connections descending to spinal cord to coordinate movements (of head position: CN8)

Question 23

how does the medial longitudinal fasciclus play a part in looking left?

result if not?

Answer 23

coordinate L lateral rectus (L abducens nuclei) connects to R medial rectus (R oculomotor nuclei)

otherwise = diplopia

Question 24

internuclear othalmoplegia

Answer 24

paralysis of eyeballs due to loss of connections between cranial nerve nuclei