Week 2 - Amblyopia

Question 1

What is amblyopia?

Answer 1

• A reduction in vision in one or both eyes, persistent after correction of refractive error.
• Absence of retinal pathology or any disease of the afferent visual pathway.
• Most common cause of vision loss in children. Interruption of normal visual development.

Question 2

Mechanisms of amblyopia

Answer 2

1. Deprivation of Form Vision
   • Can be partial or complete
   • Complete: No image/stimulus reaches fovea
   • Partial: Degraded imaging reaching fovea
2. Abnormal Binocular Interaction
   • Incomplete images fall on the retina
   • Images are incompatible
   • Eyes compete for control over cortical connections during development period-better eye gains control

Question 3

What does amblyopia look like for the Px?

Answer 3

• Reduced Snellen and grating acuity
• Loss of contrast sensitivity
• Shape distortion
• Motion deficits
• Crowding effect

Question 4

What four senses are needed for visual function?

Answer 4

1. Light sense
2. Form sense
3. Colour sense
4. Motion sense

Question 5

Describe 1. light sense and 2. form sense

Answer 5

1. Light sense
   • Most primitive
   • Ability to distinguish light and dark
   • Rods
2. Form sense
   • Ability to distinguish between spatially
   separate visual stimuli
   • Ability to discern size and shape of objects
   • Position and orientation
   • Rods and cones
   • Most acute at fovea

Question 6

Describe 1. Colour sense and 2. Motion sense

Answer 6

3. Colour sense
   • Distinguish between light of different wavelengths
   • Cones
4. Motion sense
   • Ability to detect movement of images across retina
   • Visual cortex

Question 7

What are the periods of visual development?

Answer 7

• Critical Period: A few months old - approximately 5 years old. Deprivation causes damage

• Sensitive Period: Time of deprivation- teenager years*
Amblyopia less likely to occur but improvement possible
*Some evidence in adult cases too

Question 8

Describe critical period

Answer 8

• Period with active neural plasticity (ability of the neural system to undergo change).
• Period where deprivation impacts visual development and amblyopia can develop.
• Amblyopia can only develop within this time.
• Earlier the onset of deficit + the longer the period of deprivation= worse the outcome.

Question 9

Describe sensitive period

Answer 9

• Improvement is possible during this time.
• The younger the patient= the quicker the response to treatment.
• Less common after 8 years of age.

Question 10

strabismus and the brain?

Answer 10

• Abnormally high proportion of monocular cells the visual cortex where there should be binocular cells.

•Abnormal visual cortex may be responsible for loss of binocular stereoscopic vision.

• Alternating strabismus results in equal number of cells for right and left and virtually no binocularly driven cells.

• Acuity responses in convergent eyes of monkeys reported to be reduced at the retinal ganglion cell (RGC) layer & lateral geniculate nucleus (LGN).

Question 11

Classifications of Amblyopia:

Answer 11

• Functional
Improvement after treatment is expected
- Strabismic
- Anisometropic
- Stimulus Deprivation
- Meridional
- Ametropic

• No lesion
May be reversible or irreversible
- Organic:
- Toxic

Question 12

Strabismic amblyopia:

Answer 12

Result of constant or near-constant childhood strabismus in one eye.
Mostly esotropias as many exotropia’s are intermittent in childhood.

Clinical Characteristics
•Reduced vision in one eye
• Strabismus found on CT- usually not freely alternating
• No pathology detected on ocular examination

• Occurs in 5-8% of general population
• The risk is 4x greater if one parent has strabismus
• 65% of patients impacted have a close relative with strabismus

Question 13

Anisometropic amblopia:

Answer 13

• Significant anisometropia present (At least 1D difference)
• Clearer vision in one eye for all distances
• Can be mostly spherical or mostly astigmatic

• Hypermetropia:
Most common

• Meridional (astigmatism):
Oblique astigmatism: more likely myopic

• Myopia
Can be avoided if one eye clear for distance and one clear for near

Question 14

Stimulus deprivation amblyopia:

Answer 14

• Stimulus form vision deprivation amblyopia
• One or both eyes
• Little or no light enters the eye.

• Congenital Cataract- most common
• Ptosis
• Haemangioma
• Vitreous Opacity e.g., bleeding
• Corneal Scar

Question 15

Meridional Amblyopia:

Answer 15

•Moderate-high degree of uncorrected astigmatism
•Can be unilateral or bilateral
•More significant risk in oblique astigmatism

Question 16

Ametropic Amblyopia

Answer 16

•Likely bilateral
• High degree of bilateral refractive error goes uncorrected during critical period
•Blurred vision in both eyes at all distances.
• Typically, a result of high bilateral hypermetropia 6D or greater (Cannot be compensated using accommodation)

Question 17

Organic Amblyopia: types

Answer 17

• Reversible
- Toxic Amblyopia (not always reversible)

• Irreversible
Not able to be treated. No lesion
- Nystagmus
- Albinism (usually associated with nystagmus)

Question 18

Toxic Amblopia:

Answer 18

• Painless, progressive, bilateral vision loss
• Dyschromatopsia
• May also be referred to as “toxic optic neuropathy”

• Nutrional Amblyopia
- Vitamin B12 deficiency
- Seen in patients with extreme diets- reports in patients with ASD
- May see complete/incomplete recovery with improved diet/vitamin intake

• Other common causes
- Alcohol- may be associated with B12 deficiency
- Tobacco
- Antimalarials e.g., Chloroquine
- Anticancer treatments e.g., Vincristine

Question 19

Investigations for amblopia:

Answer 19

Case History- Family history of childhood eye problems!
• Ocular Examination- Assess media and fundus
• Full Cycloplegic Refraction
• Visual Acuity Assessment: age and ability appropriate test selection
• Cover Test- is there a manifest deviation? What is the fixation preference/pattern?
• Contrast Sensitivity: Amblyopes can have reduced contrast sensitivity at higher spatial frequencies in comparison to non-amblyopes
• Uniocular fixation
• 4^ Test

Question 20

Assessment of Uniocular Fixation

Answer 20

• Assess the point of the retina that the patient is using for fixation when the other eye is occluded
• Using a visuscope or ophthalmoscope

Method:
• Dim room lights
• Ask patient to fix at distance
• Occlude “fellow normal eye”
• Line up instrument
• Get patient to fix on centre of light
• Assess where the “bright” reflex is positioned

Question 21

What can be the 3 findings when assessing the uniocular fixation?

Answer 21

• Central fixation
• Eccentric fixation
• Wandering fixation

Question 22

Central fixation and wandering fixation:

Answer 22

Central Fixation
o Object on fovea

Wandering fixation
o Uniocular condition
o Fovea has lost its fixation superiority, and no single area of the retina is used for fixation

Question 23

Eccentric Fixation

Answer 23

o Uniocular condition. Fixation is by a point which isnt the fovea.
o This point is the principle visual direction.
o The degree of eccentric fixation is defined by the distance between the fovea in degrees.
o The further from the fovea= worse the level of VA
o Estimated line reduces by 1 line per 0.5 degrees of eccentricity

Question 24

Management of Amblyopia

Answer 24

• Patients are prescribed their full refractive correction for full time wear.
• Correction of refractive error results in resolution of anisometropic amblyopia in 1/3 of 3–7 year olds
• Resolution of amblyopia in 32% of patients with strabismic and combined strabismic+ anisometropic amblyopia. Better results in strabismic only versus combined
• Refraction adaptation mostly complete by 18 weeks
• 90% have resolution by 18 weeks of refractive adaptation
• Improvement can continue for up to 30 weeks

Question 25

Occlusion Treatment

Answer 25

Occlude the non-amblyopic eye to encourage used of amblyopic eye stimulating visual development. Types of Occlusion: • Total Occlusion- excludes **light and form** vision e.g., sticky patch or fabric patch. • Total Occlusion- **excluded form vision** e.g., allows some light passage e.g., blenderm tape. • Partial Occlusion- **some form vision** but **reduces acuity** e.g., Bangerter foils Compliance has been reported to vary from 49%-87%

Question 26

How Many Hours for occlusion?

Answer 26

• **Moderate Amblyopia: 0.300-0.600** - 2 hours-6 hours when combined with 1 hour of near visual activities in children <7 years - Begin with 2 hours and if no significant improvement, increase to 6 hours. • **Severe Amblyopia: 0.700 or worse** - Full time occlusion (all waking hours or all but one) - Part time occlusion: Set hours per day In patients with strabismic, anisometropic and combined....results of 6 hours of occlusion= full time in children ages 3-7 years

Question 27

Risks of Occlusion

Answer 27

1. Intractable Diplopia: • Rare • Strabismic amblyopia • Higher risk in older children • Sbisa bar (density of suppression) assessed to monitor throughout treatment • Occlusion immediately stopped •Patients can re-suppress 2. Amblyopia develops in the other eye- rare in part time occlusion 3. Dissociation in decompensating strabismus 4. Allergic reaction: Skin reaction in conventional occlusion Allergy to atropine- local or systemic

Question 28

Atropine Penalisation

Answer 28

• Atropine is instilled (long-lasting cycloplegic agent) into the sound eye, preventing accommodation and blurring vision at near fixation. • Instilled daily or two consecutive days per week same results. • Switch of fixation- even if periodically! • Generally high rates of compliance. • Useful in mild-moderate amblyopia in patients aged 3-7 years • Conflicting evidence for its use in severe amblyopia- some reports of significant improvement

Question 29

Atropine Penalisation pros and cons

Answer 29

Pros: • Patients may be resistant to patch on face e.g., Sensory issues • Useful if patients allergic to patch- can peek from fabric patch! • Some children don’t like the appearance of the patch Cons: • Light sensitivity • Risk of allergic reaction to drop • Reported to cause nightmares

Question 30

Optical Penalisation used when:

Answer 30

• Prescription is manipulated/lenses used to blur the vision in better seeing eye- encouraging use of the amblyopic eye. - Can be used on its own or in combination with atropine. When is it used? o When cooperation with patching is poor or non-existent. o Patients with latent nystagmus. o No improvement with other treatment. o When atropine alone is not enough to reduce acuity sufficiently.

Question 31

Optical Penalisation Types

Answer 31

• Distance Penalisation: +3.50DS added to non-amblyopic eye • Near Penalization: Cycloplegia in the non-amblyopic eye with full correction and a hypermetropic lens (up to 3.00DS) in the amblyopic eye. • Total Penalisation: High hypermetropic lens added to non-amblyopic eye to induce blur at both near and distance.