Lecture 6 Amblyopia Flashcards
What is Amblyopia?
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)
Mechanism of development - Suppression
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
Mechanism of development - Stimulus Deprivation
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.
Amblyopia is diagnosed by:
Amblyopia is diagnosed by:
- 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)
- No improvement with pinhole and correction of any significant refractive error present does not improve VA to normal
- The absence of pathology to explain reduced VA
- The presence of an amblyogenic risk factor e.g. strabismus, anisometropia
What are the two definitions of amblyopia in scientific literature?
- 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)
Causes of amblyopia
Causes of amblyopia in SPEDs
Types of Amblyopia
Visual Acuity
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
Detection of Amblyopia - Refractive error
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
Detection of Amblyopia - Ocular Pathology
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
Summary of Amblyopia Detection
Full Assessment of Amblyopia
- Best corrected visual acuity (with glasses if required)
- Ocular motility
- Cover test and measurement
- Stereopsis
- Ocular movements
- Ocular pathology
- Slit lamp
- Ophthalmoscope/fundus
- OCT (scan of the retinal layers)
- Cyclopegic refraction
Why do we need to treat?
- 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
When should we treat Amblyopia?
- 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
Treatment of Amblyopia
- 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
Summary of treatment of amblyopia
Patching treatment
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)
Patching studies
Conclusion - patching treatment
- 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
Patching treatment - studies
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.
Patching recommendations
- 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)
Patching recommendations
- 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.
