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sensory systems > visual disorders > Flashcards

visual disorders Flashcards

1
Q

amblyopia

A

something that leads to an imbalance or mis-integration of the input to two eyes

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2
Q

why does amblyopia occur?

A

something has gone wrong at an early age which stops the two eyes working together

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3
Q

how do we cause monocular deprivation in animal subjects?

A

suturing one eye shut

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4
Q

what happens when one eye was sutured shut in a monkey soon after birth?

A

results in a wider ocular dominance columns from the non deprived eye

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5
Q

why is the timing of monocular domination critical?

A

the adjustment of ocular dominance columns reduces the older the animal, and the less time the eye is closed for
-large effect for age 2 and 5.5 closed 18 months
-smaller effect 10 weeks, only 4 months
-no effect 14 years for 14 months

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6
Q

Hubel and Wiesel Ocular dominance scale

A

quantifies electrophysical responses of V1 cells to stimuli applied to the left or right eye

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7
Q

following monocular deprivation, a vast majority of cells are driven…

A

exclusively by the non deprived eye

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8
Q

what drives segregation of retinal outputs? why does representation change with monocular deprivation?

A

co-ordinates waves of left or right retinal output
less firing in the deprived eye

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9
Q

amblyopia critical period cats

A

3-4 months

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10
Q

amblyopia critical period macaque

A

highly susceptible for the first 6 weeks
by 10 weeks more moderate, needs longer periods of deprivation
no effect if carried out after 1 year

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11
Q

amblyopia critical period man

A

up to age 5-10
most pronounced during first year

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12
Q

what are signals from the deprived eye suppressed by?

A

actively supressed by local interneurons

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13
Q

what can be done to induce low level responses from the deprived eye in V1 cells?

A

a blockade of local GABA signalling using Bicuculline (GABAa antagonist)

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14
Q

occlusive stroke

A

due to closure of a blood vessel
blood clot, embolism
atherosclerosis

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15
Q

what percentage of strokes are occlusive?

A

> 80%

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16
Q

haemorrhagic stroke

A

due to rupture of a blood vessel
hypertension, aneurysm

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17
Q

what is a scotoma

A

a blind or partially blind spot in the visual field

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18
Q

what can cause scotoma?

A

stroke effecting V1

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19
Q

absolute scotoma

A

no vision

20
Q

relative scotoma

A

some remaining vision

21
Q

hemianopic scotoma

A

one half of the visual field gone

22
Q

facultative/ suppression scotoma

A

in alternating foveation in squint conditions

23
Q

what artery supplies the V1 on each side?

A

the posterior cerebral artery

24
Q

occlusion of posterior cerebral artery can cause?

A

widespread loss of vision
e.g. across one full hemisphere

25
Q

homonymous hemianopia

A

loss of vision on the same side in both eyes

26
Q

homonymous hemianopia can be a result of?

A

often damage to the V1
can also be damage to other areas such as LGN, optic radiations
requires differential diagnosis/ scan

27
Q

fixation of eyes homonymous hemianopia

A

eyes fixate on everything in the scene but are only consciously aware of half of this area

28
Q

what is blindsight a result of?

A

extensive damage to the striated cortex

29
Q

what is blind sight a type of?

A

scotoma

30
Q

how does blindsight manifest?

A

patient ‘unaware’ of blind hemifield
when asked to locate a target they will protest they are blind

31
Q

what happens when a blindsight patient is asked to guess about a target located in their ‘blind’ hemifield?

A

they will do better than change
can identify orientation and some colour

32
Q

mechanisms of blindsight guesses

A

portions of V1 remain intact and active?
residual vision in higher cortices (routed through the superior colliculus/ pulvinar)

33
Q

Cowey et al. task one

A

striate cortex removed unilaterally in 4 macaques

animal fixates
fixation light goes out and 1 of 4 peripheral target comes on
animal touches the target

got a higher percentage of correct responses than chance

34
Q

cowey at al. task 2

A

striate cortex removed in 3 macaques

normal trials: target appears in one of the 5 locations in the good field – touch target

blank trials: no target appears – touch the outlined rectangle on the upper left

probe trials: a target appears in the blind field – touch this target

during probed trials monkeys responded as if no target had appeared: blindsight

35
Q

motion agnosia in Zihls patient

A
  • a patient with intact visual fields lost all perception of motion and could not distinguish between stationary and moving objects

loss of movement in all three dimensions

Due to bilateral damage of the human homologue of V5(MT)

36
Q

why is motion agnosia so rare

A

only occurs when damage to the V5 is bilateral

37
Q

neglect

A

error of the interpretation and interaction with objects in space due to parietal damage

38
Q

most extreme form of neglect

A

patient looses one half of the world

39
Q

what half of the world do neglect patients see? what is this different to?

A

they can only view the hemispace contralateral to their parietal lesion

unlike hemianopes

40
Q

what does neglect effect other than vision?

study example

A

memory of a space

patients asked to remember the names of the shops in the Piazza in Milan
-remembering the view facing south, they identified only the shops on their right
-remembering the view facing north, they name only the shops on their right

41
Q

what frame is neglect seen in

A

supra retinal reference frame

42
Q

what side of the parietal cortex is more often damaged with neglect

A

right side, loss of vision in left

43
Q

what may neglect be due to

A

competition or inability to disengage attention

44
Q

prosopagnosia

A

an object agnosia, unable to recognise objects

45
Q

agnosia

A

a loss of knowledge

46
Q

what causes prosopagnosia

A

stroke damage to the inferior temporal cortex

47
Q

prosopagnosia and facial recognition

A
  • can identify a face as a face, or parts of faces, or even emotions on faces
  • cannot recognise individual people, even close family members (potentially even own face)
  • identities are not lost, only the connections between particular faces and identities

sensory systems (17 decks)

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