visual disorders

Question 1

amblyopia

Answer 1

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

Question 2

why does amblyopia occur?

Answer 2

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

Question 3

how do we cause monocular deprivation in animal subjects?

Answer 3

suturing one eye shut

Question 4

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

Answer 4

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

Question 5

why is the timing of monocular domination critical?

Answer 5

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

Question 6

Hubel and Wiesel Ocular dominance scale

Answer 6

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

Question 7

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

Answer 7

exclusively by the non deprived eye

Question 8

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

Answer 8

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

Question 9

amblyopia critical period cats

Answer 9

3-4 months

Question 10

amblyopia critical period macaque

Answer 10

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

Question 11

amblyopia critical period man

Answer 11

up to age 5-10
most pronounced during first year

Question 12

what are signals from the deprived eye suppressed by?

Answer 12

actively supressed by local interneurons

Question 13

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

Answer 13

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

Question 14

occlusive stroke

Answer 14

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

Question 15

what percentage of strokes are occlusive?

Answer 15

> 80%

Question 16

haemorrhagic stroke

Answer 16

due to rupture of a blood vessel
hypertension, aneurysm

Question 17

what is a scotoma

Answer 17

a blind or partially blind spot in the visual field

Question 18

what can cause scotoma?

Answer 18

stroke effecting V1

Question 19

absolute scotoma

Answer 19

no vision

Question 20

relative scotoma

Answer 20

some remaining vision

Question 21

hemianopic scotoma

Answer 21

one half of the visual field gone

Question 22

facultative/ suppression scotoma

Answer 22

in alternating foveation in squint conditions

Question 23

what artery supplies the V1 on each side?

Answer 23

the posterior cerebral artery

Question 24

occlusion of posterior cerebral artery can cause?

Answer 24

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

Question 25

homonymous hemianopia

Answer 25

loss of vision on the same side in both eyes

Question 26

homonymous hemianopia can be a result of?

Answer 26

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

Question 27

fixation of eyes homonymous hemianopia

Answer 27

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

Question 28

what is blindsight a result of?

Answer 28

extensive damage to the striated cortex

Question 29

what is blind sight a type of?

Answer 29

scotoma

Question 30

how does blindsight manifest?

Answer 30

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

Question 31

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

Answer 31

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

Question 32

mechanisms of blindsight guesses

Answer 32

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

Question 33

Cowey et al. task one

Answer 33

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

Question 34

cowey at al. task 2

Answer 34

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

Question 35

motion agnosia in Zihls patient

Answer 35

* 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)

Question 36

why is motion agnosia so rare

Answer 36

only occurs when damage to the V5 is bilateral

Question 37

neglect

Answer 37

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

Question 38

most extreme form of neglect

Answer 38

patient looses one half of the world

Question 39

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

Answer 39

they can only view the hemispace contralateral to their parietal lesion unlike hemianopes

Question 40

what does neglect effect other than vision? study example

Answer 40

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

Question 41

what frame is neglect seen in

Answer 41

supra retinal reference frame

Question 42

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

Answer 42

right side, loss of vision in left

Question 43

what may neglect be due to

Answer 43

competition or inability to disengage attention

Question 44

prosopagnosia

Answer 44

an object agnosia, unable to recognise objects

Question 45

agnosia

Answer 45

a loss of knowledge

Question 46

what causes prosopagnosia

Answer 46

stroke damage to the inferior temporal cortex

Question 47

prosopagnosia and facial recognition

Answer 47

* 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