Amblyopia

Question 1

what is Strabismic amblomyopia?

Answer 1

Eye misalignment. when you’ve got the
two eyes out of alignment.
This causes some issues from the brain perspective because our
eyes share a common visual direction.
So our eyes, when they’re both pointing straight ahead when
we’re actually looking at something, we’re fixating on something.
The image images for each eye will fall on the
phobia of each eye.
And as far as the brain is concerned, the phobia
represents straight ahead. Causes double vision

Question 2

Mono-ocular deprivation

Answer 2

Strabismic = Eye misalignment
Anisometropic = Image aneisokonia
stimulus deprivaiton

Question 3

Anisometropic

Answer 3

Image aneisokonia. you have a difference in
the glasses prescription between the two eyes.
So you’ve got one eye that may be relatively more
plus or minus than the other.
And so you know, there’s obviously asymmetrical levels of image
blur between the two eyes.

Question 4

stimulus deprivation amblyopia.

Answer 4

So you can have as a child, you can have
like, a droopy lid, or you can have, um, a
cataract in one eye and not the other.
Um, anything that stops the light from getting to the
back of the eye can also cause amblyopia.
Um, so you know those are examples of what
we call monocular amblyopia.
OK, so it only affects one eye and not the
other well,

Question 5

bin-ocular types of amblyopia?

Answer 5

So another big angiogenic risk factor is refractive error.
So any kind of glasses prescription, if it’s big enough,
can actually cause that underdevelopment of the connections between the eye and the brain.
So if you have binocular image blur, then you can
actually get a form of amblyopia that affects both eyes.
The connect between the eye and the brain are just
not that well developed because you don’t have a very
good quality visual image.

Question 6

Spatial frequency

Answer 6

visual acuity

Question 7

Vernier acuity

Answer 7

Vernier acuity, which is where you
show somebody a line in relation to another line, and
you ask them to figure out whether the line is
in alignment or not.
Is it in line, or is it out of line
and if so, which direction?

Question 8

How is contrast sensitivity affected?

Answer 8

For strabismic amblyopia, there is a drop off in contrast sensitivity deficit. There is a higher spatial frequency deficit. But for Ansiometropic amblyopia
and stimulus deprivation
amblyopia, it’s actually any spatial frequency that you get that
change.
there is that drop off for any spatial frequency.

Question 9

How are vernier and grating acuities affected?

Answer 9

Both are impacted and decrease.

Question 10

what is the main aspect of ablomyopia?

Answer 10

binocular vision is one of the primary mechanisms of
amblyopia

Question 11

what do characterisitcs of different types of amblyopia show as evidence?

Answer 11

Limited differences within groups of amblyopia.
Early evidence for the role of decorrelated Binoocular vision.

Question 12

Diff btw strasbic amblomyopia and Anisometropic amblomyopia?

Answer 12

But the actual main difference between these two groups is
that the strasbics , the ones with the eye misalignment, don’t
have as much impaired contrast sensitivity Ihowever impaired visual acuity) compared to the asinometropes and other non strasbics that aren’t associated with that eye misalignment.
So that’s pretty interesting. So you’ve got a bit of a dichotomy here.

Question 13

Treatment affects what aspects of amblomyopia? What things does it not treat soemtimes?

Answer 13

when we treat amblyopia, we address the
local deficits, the primary contrast sensitivity and visual acuity deficit.
OK, those things get better when you treat amblyopia.
But actually we have deficits in other areas (global) in amblyopia
as well. Such as

Motion processing
Form processing
Veridical perception
Stereopsis

Question 14

How do global defects result?

Answer 14

Local’ deficits cascade to affect processing in
extrastriate visual cortex, but improving high contrast visual acuity does not always translate into complete resolution of ‘global’ deficits in motion processing, Form processing, Veridical perception, Stereopsis

Question 15

What are the cortical changes in response to amblomyopia?

Answer 15

we get cortical changes **( V2 AND V3) **in relation to
the areas that are responsible for disparity detection.
And disparity is one of our crucial, um, mechanisms for
stereopsis. lOSS OF STRIPES IN VISUAL CORTEX

Question 16

What is the relationship between behavioural and

Answer 16

Behavioural losses exceeds that explained by physiological changes in numbers of visual cortical cells driven by the deprived eye, i.e. cortical neurons driven by amblyopic eye responded to Contrast Sensitivity and Spatial Frequencies not detected psychophysically.

Question 17

In severe amblomyopia what changes occur to eye dominance?

Answer 17

Number of cortical cells driven by one eye.
There is profound bias btw the two eyes. But in less severe amblomyopia there may be less significant skews. So the cases that had the most significant loss of input of amblyomyopic eye to cortex.

Strasbics skew wasn’t so significant.

Question 18

how do underactivation of straite cortex impact extrastriatal cortices?

Answer 18

Underactivation of striate cortex seems to be correlated with underactivation in extra-striatal cortices as well.

Question 19

Can contrast senstivity deficits predict whats happening?

Answer 19

We’ve got this V 1 activation deficit, which then correlates
quite nicely with the extra striate deficits.
But actually, the contrast sensitivity deficit alone is not enough
to actually predict what’s going on with that

Question 20

2 theories that explain amblomyopia?

Answer 20

Neural disarray
-Mislabelled cortical projections
-Cell responding to stimulation in one area of visual space -> retinotopic representation of different, nearby area of space
-Fundamental distortion positional
**Undersampling **
- receptive field size/spacing in central field = normal peripheral retina
- Increased positional uncertainty/distortion, temporal instabilities

Question 21

What is a limitation of Levi’s theory?

Answer 21

because under sampling
is only really effective at explaining like a limited number
of types of amblyopia.
Um, because it doesn’t, it doesn’t really account for detection.
Um, deficits.
It’s literally only about that discrimination side of things.

Question 22

How did Levi change his theory?

Answer 22

So later on, he was like, Oh, maybe instead of
it just being fundamental under sampling, maybe it’s more like
irregular sampling.
So you’ve still got this loss of cortical cells.
But it’s just that you’ve also got a little bit
of this, this disarray going on as well.

Question 23

Which theories work?

Answer 23

• you can get both types of anomalous
  processing in the same Amblyope
• Neither theory completely explains the behavioural deficits
• May depend on Amblyopia type

Question 24

What is the updated theory of these two ideas?

Answer 24

• demonstrated that both of these theories can come off
  the same sampling framework.
• • Neural disarray= spatial disorder without a loss of samples = irregular sampling
• Main contributer but still only at high Spatial frequencies
• Undersampling = fewer samples within regular or irregular array
• *Limited contributor *and only at high SFs

Question 25

So how can this distorted visual perception of some amblyopes be experienced in some but not others?

Answer 25

So, you know, for the under sampling side of things, you've got this larger, receptive field and lower sensitivity to the position of individual stimuli. And then for the neural disarray theory. You've just got stuff projecting to the wrong place, and you end up with this mixed up visual image.

Question 26

Limitation of these two theories in conjunction?

Answer 26

But the thing with these theories is that they don't actually explain why things like the Vernier deficit happen over a range of different contrasts. theory doesn't completely explain all of these **behavioural** **deficits** again because these theories are kind of about scrambled visual input rather than, you know whether or not a stimulus can be detected **so that sampling still occurs. assumingly ** So under that theory, you would still be able to detect the stimulus. And it's just the discrimination of it That's the issue. **Whereas actually, we know that there's both detection and discrimination deficits in amblyopia.**

Question 27

What is an example that can be explained by the theory?

Answer 27

Anisometropic Amblyopia. the level of perceptual visual distortions that can be recorded are similar in magnitude and type to those that can be induced in visually normal participants by blurring visual acuity using plus lenses. So this states that this high spatial frequency loss is sufficient to kind of describe that type of visual distortion in Amblyopia . all you need to do is just put up some refractive blur, then you know, it's kind of an under sampling theory is kind of sufficient to really kind of explain that because you've just got that loss of that loss of visual information.

Question 28

What is occuring at higher order visual areas that limits detection?

Answer 28

**have a detection deficit and that this is kind of associated with terrible pooling at V four. So V four is where a lot of the visual information gets integrated to make decisions about global stimuli.** *So your global motion and your global form perception is based on the integration of individual orientation and motion view across the entire image.* **integrating everything across the whole image, like regardless of whether it's correct or incorrect, then you can end up with those kind of detection deficits.**

Question 29

Internal noise theory?

Answer 29

iS IT EARLY OR LATE IN PROCESSING? idea that The primary contrast sensitivity deficit of V 1 is just being compounded later on by just mismatch templates, which is the neural disarray theory. And then combining all of that together with this noisy decision template and undersampling.

Question 30

Internal noise thoery

Answer 30

sampling anomalies in v1

Question 31

What does reconstruting images using amblyopia quantitative measurements of distortion demonstrate?

Answer 31

Quantitatively measiuring distrotions and constructing images. Amblyopes said that wasn't what it looks like.. research shows that there is something else going on that maybe there is this fundamental disconnect between what we measure quantitatively and what we actually perceive.

Question 32

if there is some capacity to interpret the visual image, is it possible to actually train the brain to make better use of that information?

Answer 32

Well, this also depends on how well we're actually using the information from the Amblyopic eye to begin with.

Question 33

Suppression or inattention?

Answer 33

CLosing fellow eye in strasbic , amblyopic eye resutled in undercounting (suppression) but when the the other good eye was opened undercounting was worse so perhaps good eye was inhibiting input from strasbic eye. In Anisometropic, there isn't much suppression but still undercounting perhaps due to attentional deficits.

Question 34

What could be causing the noise?

Answer 34

Perhaps input from amblyopic eye.

Question 35

What does the experiment involving undercounting indicate?

Answer 35

Perhaps suppression is just a type of anamalous binocular interaction

Question 36

Can we balance the eyes? How can we do so? What does this tell us about suppression?

Answer 36

the level of suppression is a affected by the level of stereopsis. So your level of stereopsis actually impacts on how likely you are to pay attention to that input from the Amic eye. so **contrast, balancing the two eyes can actually result in binocular rivalry in both eyes being used simultaneously, **

Question 37

What indicates that amblyopia is a binocular problem?

Answer 37

So for strasbic amblyopia the brain uses that eye more than we thought it did. And so if you balance the contrast, you could actually resolve some of these extra strite visual processing deficits. So what we sort of decided is that amblyopia? You know, we used to say it was a monocular condition, but actually it's a binocular problem. So amblyopia a period is a condition which renders a binocular system functionally monocular.

Question 38

Treatments for amblyopia?

Answer 38

Using a an eye patch to encourage amblyopic eye to work harder. Doesn't resolve higher order deficits. Videogames is a possible solution as you can spend more time allowing perceptual learning to take place. Perceptual leaning may improve many aspects of visual function but it requires many hours of training. Many things impact results: age, complaince, game used, previous treatment etc