Amblyopia Lecture 12

Question 1

What is amblyopia commonly known as?

Answer 1

Lazy eye

Question 2

What is amblyopia?

Answer 2

A developmental disorder of vision

An imbalance between the two eyes

Question 3

Who does amblyopia affect and why?

Answer 3

Children and it affects them because it can not be corrected with spectacles.

Question 4

What is the most common causes of amblyopia?

Answer 4

anisometropia (blurring in one eye, other is sharp i.e refractive error b/w eyes)

Strabismic amblyopia (Misalignment between the eyes)

Question 5

What can cause amblyopia in third world countries?

Answer 5

Congenital cataract

deprivation amblyopia

Question 6

What are the implications of a child having amblyopia?

Answer 6

Once amblyopia has developed vision does not improve even if glasses correct the eye component (can do sometimes…)

I.e visual loss has a cortical basis

Question 7

Why may amblyopia cause cortical change?

In lay man terms

Answer 7

Because when the child is growing they receive a bad visual diet and this alters cortical structure in development,

Question 8

What is the nature of amblyopia impairment?

Answer 8

Impaired monocular vison:

• Acuity (poorer)
• Sensitivity to contrast (reduced)
• Spatial distorsions (i.e fractures in reproduced drawings of lines)

Question 9

For diagnosis of amblyopia using an letter chart what must occur?

Answer 9

There must be a two line difference between the impaired eye and the follow eye.

Question 10

What is the most diagnostic tool of amblyopia?

Answer 10

Crowding

(everyone experiences crowding which caused by less dedication to the peripheral field so it is in poor quality i.e can’t distinguish letters)

People with amblyopia experience crowding centrally in their affected eye.

Question 11

What has crowding been likened to?

Answer 11

Crowding is like seeing images as texture.

overall properties of things. i.e recognise a russian book as lines of writing.

Amblyopia is like crowded vision

Question 12

Are crowding and loss of acuity etc all seperate things?

Answer 12

No it is likely that they are all linked and a result of one another.

Question 13

How does amblyopia affected binocular vision?

Answer 13

• Impaired stereopsis (sense of depth)
• Suppression (cause or symptom?) (abnormal binocular input results in the the worse eye being ignored/ better eye being favoured, input of bad eye surpassed)

Question 14

what is suppression?

Answer 14

Intraoccular suppression is when one eye s output is suppressed and the others is favoured.

Question 15

In new zealand how many children have amblyopia?

Answer 15

3%

Question 16

What are the monocular treatments for amblyopia?

Answer 16

• Patching and atropine (eye drop)

Question 17

How often is acuity improved with patching and whats the compliance of patching?

Answer 17

70% reported acuity improvement

40-60% compliance (poor)

50% dont gain stereo vision back (proper binocular vision)

Question 18

Whats the concept of patching?

Answer 18

Patch the better seeing eye to make the amblyopic eye work harder and correct.

Question 19

How does atropine work?

Answer 19

Eye drops go into better seeing eye and it makes things blurry.

(has to wear off and can’t be taken off thus better compliance)

Question 20

What are the treatments for amblyopia in adults?

Answer 20

No treatments

Question 21

Why are there no treatments for adult amblyopia?

Answer 21

Beyond the critical period. (deprivation drives loss and treatments don’t really work as not so plastic any more)

Question 22

What part of the cortices are first looked disrupted in amblyopia?

Answer 22

The LGN

Question 23

What is a histological feature of amblyopia in the LGN?

Answer 23

Cell body shrinkage in cells that receive input from the amblyopic eye.

Question 24

How doe the LGN function in amblyopia?

Answer 24

Normal or only slightly abnormal function

Question 25

Why is there a light function and histological discrepancy in the LGN in amblyopia?

Answer 25

Minority of cells ~6% feed forward, most are modularity.

Anaesthesia affects LGN studies….. (so these rat studies are unreliable but we can use MRI..)

Question 26

What does MRI of amblyopia in the LGN show?

Answer 26

Reduced grey matter in strabismic amblyopes. (quite reduced)

Question 27

What does a functional (blood flow) MRI show in the LGN of someone with amblyopia?

Answer 27

Reduced LGN activation when driven by the amblyopic eye. (substantial difference between the eyes)

Question 28

Does amblyopia affect a particular parallel l processing pathway in front he LGN?

Answer 28

Parvocellular loss would be consistent with a loss in visual acuity.

Question 29

How would you measure if the parallel pathways were affected?

Answer 29

Accesse funtional activation for stimuli targeting different pathways. (m, p, k)

Question 30

Using stimuli to access parallel pathway processing, what dot he results indicate?

Answer 30

selective loss of the parvocellular response at the LGN in adult amblyopes.

Question 31

How else can parallel pathways function be assessed?

Answer 31

By using high (parvo) vs low (magno) contrast stimuli. you can assess function by measuring activation of these pathways.

Question 32

What is seen using contrast stimuli in amblyopic patients ?

Answer 32

Only a small loss of low contrast response for the amblyopic eye. (low difference)

But

There is a big difference in activation for high contrast response that is a high loss of response in the amblyopic eye for high contrast stimuli. - consistent with a parvocellular deficit.

Question 33

What is the idea of patching?

Answer 33

A method to overcome suppression but shutting down completely the input from the fellow eye.

Question 34

Describe a binocular treatment for amblyopia:

Answer 34

Using manipulation of contrast in the fellow eye in a binocular tool to overcome suppression and improve stereo vision. (depth)

Question 35

Whats an example of binocular treatment to improve stereo vision? in the lab

Answer 35

Perceptual learning - improving acuity, contrast, orientation by repeated performance of an acuity task.

Flaw- hard to get compliance in kids

Question 36

Whats an example of binocular treatment for amblyopia that is targeted at kids? that uses a different form of patching

Answer 36

First person video games with a patch. Gains in acuity better and faster than traditional patching (no stereopsis gains)

Question 37

What is active suppression therapy?

Answer 37

Uses a tetris video game. improves acuity rapidly and stereopsis!!! (binocularity) - don’t see in regular patching (must use 3d for stereo)

Has red/blue glasses and the blocks are designed to be seen by the different eyes Requires the eyes to work together to succeed. Cant win if the glasses aren’t used thus good compliance.

Question 38

What are the limitations of recent innovations of treatment?

Answer 38

• Mechanisms of improvement unknown
• Critical components unknown i.e what makes it work better.
• Not tested on children

Question 39

What does his treatment involve?

Answer 39

Watching movies with specialised ski goggles.

• They manipulate depth relative to background plane.
• Blur to unaffected eye to match crowded acuity in affected eye. (like patching)

High compliance

Every minute, vac man comes up and he must eat the whitest ghost (black to one eye and white to the other), this measures suppression. Glasses are required for ghosts. no ghost = non compliant. This also shows eye preference.

After 2 months, acuity improved 3 lines.

Good improvements in stereo acuity.

Shows that intraoccular suppression remains largely unchanged. Despite acuity and stereopsis.

Therefore suppression is a manifestation of amblyopia not the cause.

Question 40

What are the conclusions?

Answer 40

Both LGN and visual cortex are susceptible to abnormal development

Functional deficits are consistent with a primary parvocellular loss

Binocular stimulation treats amblyopia
- not reduction in intraoccular suppression.