3 - visual pathway and defects lecture

Question 1

what are the 2 main types of photoreceptors?

Answer 1

> RODS (roughly 100 million)
- vision in low lighting conditions, peripheral vision, low resolution

> CONES (roughly 6 million)
- detailed vision, colour vision, brighter light

Question 2

what is in the fovea? (centre of the eye)

Answer 2

cones only

Question 3

what forms the optic nerve?

Answer 3

axons of ganglion near inner surface of retina

Question 4

what do ganglion cells do?

Answer 4

transmit the visual signal out of the eye as a series of impulses

Question 5

what are horizontal and amacrine cells?

Answer 5

laterally interconnecting neurons that modify the visual signal

Question 6

what do bipolar cells do?

Answer 6

connect (usually multiple) photoreceptors to ganglion cells

Question 7

what 4 subcortical regions does the retina project to?

Answer 7

> primary visual pathway (image forming vision):
1) lateral geniculate nucleus

> secondary visual pathway:
2) superior colliculus - eye movements
3) hypothalamus - circadian rhythm
4) pretectum - pupil

Question 8

light from nasal side hits ______ retina and light from below hits _____ retina

Answer 8

nasal side hits TEMPORAL side
light from below hits SUPERIOR retina

Question 9

nerves from what aspect of the eye cross over/dessucate at the optic chiasm?

Answer 9

nasal aspect of eye

Question 10

where do retinal ganglion cell axons synapse?

Answer 10

lateral geniculate nucleus

Question 11

describe the 2 parts of optic radiation

Answer 11

• some bits have a straighter path — go through PARIETAL lobe — have fibres from SUPERIOR retina
• some fibres loop into TEMPORAL lobe and contains fibres from the INFERIOR retina
• both bits of optic radiation end up in the visual cortex

Question 12

what is the blind spot?

Answer 12

• where the optic disc is — no photoreceptors
• it is where the ganglion have all converged
• it sits nasally, therefore blind spot is temporal

Question 13

what are some retinal causes of visual field defects?

Answer 13

• vascular — retinal artery occlusion, retinal vein occlusion
• retinal detachment
• macular lesion — central defect

Question 14

what are some causes of visual defects from the optic nerve?

Answer 14

> glaucoma
optic neuritis — inflammation of nerve eg. in MS
optic atrophy
optic nerve compression — thyrotoxicosis, tumour

Question 15

what are some causes of visual defects from a lesion at chiasm?

Answer 15

tumours — esp pituitary tumour

Question 16

what are some causes of visual field defects from a lesion after the chiasm?

Answer 16

• stroke
• tumour

Question 17

what are some causes of visual field defects from the occipital cortex?

Answer 17

• stroke
• tumour

Question 18

is there is a retinal detachment superonasally, where is the defect?

Answer 18

inferotemporally

Question 19

what does a lesion at the optic chiasm result in?

Answer 19

a bitemporal hemianopia

Question 20

what fibres cross at the optic chiasma?

Answer 20

nasal

Question 21

what happens if the optic nerve is completely bisected?

Answer 21

lose vision in that eye

Question 22

lesion in visual cortex — can tell its more likely to be in the visual cortex than radiation due to ______?

Answer 22

macula sparing

Question 23

macula sparing — lesion likely to be in _____?

Answer 23

visual cortex

Question 24

what are 2 theories of macula sparing?

Answer 24

1. macula represented in really large region of the visual cortex. it is detailed, important therefore massive infarct needed to wipe it out
2. the area of the visual cortex that has macula vision has 2 blood supples — middle and posterior cerebral arteries — both would be need to be blocked to wipe out its supply

Question 25

PITS acronym?

Answer 25

P arietal lesion cause
I nferior defect
T emporal lesion causes
S uperior defect

Question 26

inferior visual field loss — optic radiations in _____ affected?

Answer 26

parietal lobe

Question 27

superior visual field loss — optic radiations in ________ affected?

Answer 27

Meyer’s loop (temporal lobe)

Question 28

visual field defects summary

Answer 28

Question 29

a patient presents with a right sided homonymous hemianopia. where is the lesion likely to be?

Answer 29

left optic tract or left optic radiation (it affects both divisions of the radiation)

Question 30

name 2 conditions that can cause a right sided homonymous hemianopia

Answer 30

• stroke
• tumour

Question 31

a patient is found to have a bitemporal hemianopia. where is the lesion likely to be?

Answer 31

optic chiasm

Question 32

which medical condition can cause a bitemporal hemianopia?

Answer 32

acromegaly

Question 33

if a patient has an inferior retinal detachment, what kind of visual field defect will they have>?

Answer 33

superior visual field defect

Question 34

you notice a patient has macula sparing when he has formal visual field testing done. where is the lesion likely to be?

Answer 34

visual cortex

Question 35

what type of photoreceptor is responsible for colour vision?

Answer 35

cones

Question 36

if a patient has a left inferior quadrantanopia, where is the lesion?

Answer 36

right optic radiation in the parietal lobe