Lecture 6 Amblyopia

Question 1

What is Amblyopia?

Answer 1

Amblyopia translates to dim-sightedness.

It is reduced visual acuity which cannot be explained by ocular pathology or refractive error. Amblyopia is a sesnory consequence of:

• Prolonged impaired or degraded visual input presented to one or both eyes and,
• Dysfunction of the processing of visual information occurs during the period of neural plasticity

Amblyopia is the most common cause of monocular vision loss (1-5% of the population)

Question 2

Mechanism of development - Suppression

Answer 2

If suppression occurs frequently e.g. in constant strabismus or in intermittent strabismus if the eye is turning often…

• This can, through the lack of use lead to amblyopia
• Competition between different images e.g. fron anisometropia leading to the suppression of one image

Question 3

Mechanism of development - Stimulus Deprivation

Answer 3

Stimulus deprivation: the image to one or both eyes is unclear or absent due to high refractive error or pathology e.g. ptosis or congenital cataract.

• Results in under-developed vision and severely reduced VA (especially when there is complete deprivation e.g. from pathology)

Amblyopia occuring through both mechanisms tends to be more severe.

Question 4

Amblyopia is diagnosed by:

Answer 4

Amblyopia is diagnosed by:

1. Reduced visual acuity:
   
   • A difference of 2 or more lines in visual acuity (unilateral)
   • VA significantly reduced from what is expected according to age (bilateral - uncommon)
2. No improvement with pinhole and correction of any significant refractive error present does not improve VA to normal
3. The absence of pathology to explain reduced VA
4. The presence of an amblyogenic risk factor e.g. strabismus, anisometropia

Question 5

What are the two definitions of amblyopia in scientific literature?

Answer 5

• Inter-ocular difference (IOD) in VA of 2 or more lines
  
  • e.g. R: 6.9.5 L: 6/6
• Reduced best corrected visual acuity in one or both eyes (MEPEDS, BPEDS, SPEDS, SMS studies)
• younger than 4 years < 6/15
• 4 years or older < 6/12
• In the absence of pathology
• With an amblyogenic risk factor present (strabismus or high refractive error)

Question 6

Causes of amblyopia

Answer 6

Question 7

Causes of amblyopia in SPEDs

Answer 7

Question 8

Types of Amblyopia

Answer 8

Question 9

Visual Acuity

Answer 9

The diagnosis of amblyopia according to our definition relies heavily on the measurement of VA

This requires an accurate test that is sensitive for the detection of amblyopia and age-appropriate for the patient

• Recognition acuity charts are better than TAC or CAT (but may not be appropriate for very young children)
• Picture charts (apart from Lea) are unstandardised and not sensitive for amblyopia
• Crowding is essential

Question 10

Detection of Amblyopia - Refractive error

Answer 10

Need to confirm that there is still a difference in VA (of at least two lines between the two eyes for unilateral amblyopia) or reduced age-norm VA (in both eyes for bilateral amblyopia) AFTER refractive correction.

• Pinhole isn’t enough to confirm that the reduced VA is not refractive
• Need to reveal the full refractive error, e.g. cyclopegic refraction for children
• Best corrected VA required for a definitive diagnosis

Question 11

Detection of Amblyopia - Ocular Pathology

Answer 11

We must confirm that the reduced VA is not due to pathology

• Check fundus and for clarity of cornea, lens etc
• Where pathology is presented and the likely cause of the amblyopia (stimulus deprivation) eg. congenital cataract, this should be removed and residual vision loss could be considered the result of amblyopia

Question 12

Summary of Amblyopia Detection

Question 13

Full Assessment of Amblyopia

Answer 13

1. Best corrected visual acuity (with glasses if required)
2. Ocular motility
   
   • Cover test and measurement
   • Stereopsis
   • Ocular movements
3. Ocular pathology
   
   • Slit lamp
   • Ophthalmoscope/fundus
   • OCT (scan of the retinal layers)
4. Cyclopegic refraction

Question 14

Why do we need to treat?

Answer 14

• Treatment improves VA and binocularity (especially important for promoting control in intermittent deviations)
• In untreated amblyopia, visual acuity continues to decline over time and amblyopia becomes more dense during the period of plasticity
• Amblyopia remains the most common cause of uniocular vision loss in adults between the ages of 20 and 70 years
• When someone is amblyopic, it puts them at greater risk of visual disability when their good eye is affected by trauma or disease, e.g. AMD or other retinal conditions

Question 15

When should we treat Amblyopia?

Answer 15

• Treatment is most effective in younger children < 8 years of age
• There is some evidence that VA can be improved in older children and teenagers up to 17 years although VA gains may be less and improvement slower
• Some potential for improvement of VA in adults but still being investigated and it is uncertain whether the effects are maintained long-term

Question 16

Treatment of Amblyopia

Answer 16

• Prior to treating the amblyopia directly, treat the cause, e.g. pathology
• Next refractive error needs to be corrected as the first line of treatment
• Further treatment is designed to increase the use of the affected eye by penalising the other good eye
  
  • Occlusion/ Patch - partial or total form occlusion
  • Atropine occlusion - paralyse accommodation to blur image
• Strabismus surgery is usually performed after amblyopia treatment to promote binocularity

Question 17

Summary of treatment of amblyopia

Answer 17

Question 19

Patching treatment

Answer 19

Prescribed occlusion depends on the:

• Severity of the amblopia
• Age of the child
• Compliance

Patching can be full-time or part-time. Patches can be total to form (worn part time) or partial (bangerter filter - worn full time on glasses)

Question 20

Patching studies

Answer 20

Question 21

Conclusion - patching treatment

Answer 21

• For severe amblyopia (6/30 and above): part-time patching (6hours per day) is as effective as full-time patching]
• For mild (6/9-6/12) - moderate amblyopia (6/12 - 6/24): 2 hours of patching is equivalent to 6 hours
• A bangerter filter worn over glasses full-time was equivalent to 6 hours of total-to-form patching
• Clinicians often prescribe near activities while the patch is being worn. Although there is no evidence that this helps treatment, it may help with compliance

Question 22

Patching treatment - studies

Answer 22

MOTAS and ROTAS studies

• Used occlusion dose monitors to assess how much patch was worn - < 50% prescribed time
• Best VA was achieved with 170 hours of occlusion under age of 4
• Best VA was achieed with 236 hours of occlusion over age of 4

References

Stewart et al. MOTAS Cooperative, Modelingdose –response in amblyopia towards a child-specific treatment plan. Invest OphthalmVis Sc. 2007 :48 2589-94

Wallace, M. P., Stewart, C. E., Moseley, M. J., Stephens, D. A., & Fielder, A. R. (2013). Compliance With Occlusion Therapy for Childhood AmblyopiaComplianceWith Occlusion Therapy. Investigative ophthalmology & visual science, 54(9), 6158-6166.

Question 23

Patching recommendations

Answer 23

• Begin with lower patching time total to form and increase if VA is not improving (patient should be monitored every 4-6 weeks)
• Start with 2 hours of patching every day, regardless of their VA
• If they are not improving - increase the patching time up to 6 hours per day (may be necessary for severe amblyopia and older children)
• Most improvement in vision occurs in the first 12 weeks (PEDIG)
• While 90% show improvement, only 50% achieve ‘normal’ or equal VA (PEDIG)

Question 24

Patching recommendations

Answer 24

• If improvement stops and amblyopia remains, consider changing treatment or increasing patching time
• If no further improvement is made, deal with compliance issues and then consider ceasing treatment if all else fails
• Reoccurrence after treatment is common and patients should be monitored for at least a year.

Question 25

Ocular therapy and its impact on ocular alignment

Answer 25

Suspension of fusion with occlusion can potentially increase the angle of the deviation or break intermittent strabismus into constant

• Similar amounts of deterioration and improvement of alignment was found after completion of occlusion treatment in a group of 161 patients
• Some children who initially appeared straight became esotropic (less than 8) and other children with small angle strabismus progressed to a larger angle (18%)
• The same amount of children improved to an orthotropic position or reduced the angle of their esotropia (19%)

Question 26

Steps to treatment of amblyopia - Summary

Answer 26

Question 27

Steps to remove pathology

Answer 27

Amblyopia cannot be treated until pathology is removed otherwise, amblyopia treatment will not be successful

• Cataract removal and IOL replacement
• Corneal transplant
• Ptosis repair
• Amblyopia in cases of stimulus deprivation (especially unilaterally) can be severe and early treatment is more likely to be successful

Question 28

Treatment of Amblyopia - Prescribe glasses

Answer 28

• Full time wear of appropriate refractive correction improves amblyopia in both strabismic and anisometropic amblyopia
• About a quarter of children with amblyopia reached equal visual acuity with refractive correction alone
• Prior to commencing any patching treatment, it is suggested that a period of refractive adaptation be observed
  
  • AAO PPP suggests 18 weeks
  • Oter guidelines suggesr until VA is stable
• See the patient 2-4 weeks after prescription to check the glasses are correct and being worn
• Monitor patients with glasses every 6-12 weeks for VA again

Question 29

Prescribed glasses

Answer 29

Question 30

Patching recommendations

Answer 30

• Start with 2 hours of patching time per day with total to form occlusion, regardless of their initial VA
• If they are not improving - increase the patching time up to 6 hours per day (may be necessary for severe amblyopia and older children)
• The patient should be monitored every 4-6 weeks
• Most improvement in vision occurs in the first 12 weeks

Question 31

Patching recommendation - continue

Answer 31

• If improvement stops and amblyopia remains, consider changing treatment or increasing patching time
• If no further improvement is made, deal with compliance issues and then consider ceasing treatment if all else fails
• Reoccurrence after treatment is common and patients should be monitored for at least a year or until 8 years of age
  *

Question 32

Atropine vs Patching

Answer 32

• Atropine works by paralyzing the ciliary muscle and increasing the pupil size
  
  • Glare from dilated pupil
  • Children who are hyperopic (majority) will be unable to accommodate to overcome refractive blur
• One drop of atropine 1% has some effect for up to 2 weeks and may not need to be instilled daily (although daily atropine is often prescribed)

Question 33

Atropine vs Patching

Answer 33

6 hours per day of occlusion compared to Atropine 1% drop every day

• 419 children in study aged 3-7 years -Strabismic, Anisometropic and mixed
• Improvement was faster in the patching group compared to the Atropine group but after 6 months there was only 1/2 a line difference between groups
• At 2 year follow-up VAs were exactly the same for each group
• Weekend applications of Atropine 1% drop, e.g. Saturday and Sunday was just as effective for outcomes as daily application (long lasting dosage)
• VA results were greater when a plano lens was utilised in addition to atropine in the non-amblyopic eye than atropine alone
• Weekend atropine in severe amblyopia improved VA by 4.5-5.1

Question 34

The problem

Atropine vs patching

Answer 34

The problem:

• Reverse amblyopia
• Atropine has severe systemic side-effects
• Parents tend to struggle to get the drops in
• Drops are painful

Most ophthalmologists only consider atropine if their non-compliance with wearing the patch

Question 35

Compliance

Answer 35

Educating the child as well as the parent about the importance of wearing their patch

Activities for the child around the patch, e.g. decorating their own patch or colouring in pirate pic…

Some children may be more likely to wear the patch at home and others may prefer supervision at school

Star charts and pictures where the patch can be stuck on for rewards