Psychology 4051

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Psychology 4051

• Amblyopia

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Amblyopia

• Lazy Eye a substantial reduction in vision in
  the absence of any detectable optical or retinal
  abnormalities.
• Can exist bilaterally but is usually unilateral.
• Defined as a two-line difference (i.e., 0.2
  logMAR) difference on a visual acuity test.
• While wearing best correction.

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Amblyopia

• Most common cause of monocular vision loss in
  children.
• Prevalence is between 0.2 and 5.5
• Approximately 5 in Newfoundland.

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Types of Amblyopia

• Caused by vision disorders that disrupt normal
  visual experiences during the critical period.
• There are three types of amblyopia.
• Classified by the cause of amblyopia
• Amblyogenic factor

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Types of Amblyopia

• Strabismic Amblyopia caused by strabismus.
• The most common form of amblyopia.
• A misalignment of the eyes.
• Esotropia One or both eyes are misaligned in the
  inward position.
• Exotropia One or both eye are misaligned in the
  outward direction.

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Types of Amblyopia

• The misaligned eye receives a completely
  different image.
• Can lead to diplopia.
• Anisometropic Amblyopia Caused by anisometropia.
• Anisometropia Unequal refractive error between
  the eyes.
• Have a strong eye and a weak eye.
• Usually refers to a difference of 1.0 to 1.5 D.

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Types of Amblyopia

• Image Degradation Amblyopia caused by an optical
  obstruction that prevents the formation of a
  sharp, clear image in one eye.
• Cataracts and Ptosis

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Types of Amblyopia

• In each case, the image from the affected eye
  (weaker or misaligned) eye is suppressed.
• Cortical connections from the affected eye
  regress.
• The suppression becomes permanent.
• There is a reduction in the number of binocular
  cortical cells.
• Leads to a lack of stereopsis or poor
  stereoacuity.
• Also leads to reduced visual acuity and contrast
  sensitivity.

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Summary

• Amblyopia is caused by the existence and
  persistence of a monocular visual problem during
  the period of plasticity.
• This affected eye is placed at a disadvantage in
  the formation and preservation of neural
  connections to the visual cortex.
• The anatomical/physiological result is that few
  cells in the visual cortex will be driven by the
  amblyopic eye.

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Summary

• Furthermore, few cells will be binocular.
• The visual effects are reduced visual acuity,
  contrast sensitivity, vernier acuity, and
  stereopsis/stereoacuity.
• Because the effects are cortical in nature, these
  problems will persist even when the amblyogenic
  factor is treated.

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Treatment of Amblyopia

• The first step of treatment is to correct the
  amblyogenic factors.
• Strabismic amblyopia
• The strabismus is treated first.
• This can be treated by muscle surgery.
• Some patients have accommodative esotropia due to
  high hyperopia.

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Treatment of Amblyopia

• They are so severely hyperopic that their lenses
  must accommodate to see relatively distant
  objects.
• There is a relationship between how much we
  accommodate and how much the eyes converge.
• Patients with accommodative esotropia accommodate
  so much that their eyes over-converge.

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Treatment of Amblyopia

• The patient attempts to fixate the x.
• Because he/she is excessively hyperopic, each
  lens must accommodate to see the object.
• Because of the relationship between accommodation
  and convergence, the eyes will converge.
• Based on the amount of accommodation, the eyes
  will over-converge.

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Treatment of Amblyopia

• Accommodative esotropia is treated with glasses

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Treatment of Amblyopia

• Anisometropic amblyopia
• Corrected with glasses.
• Image Degradation amblyopia
• Cataracts are removed by removing the lens.
• An intraocular lens (IOL) can be implanted.

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Treatment of Amblyopia

• Severe ptosis can be treated surgically.

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Treatment of Amblyopia

• In some cases the amblyopia will resolve in
  response to spectacle correction alone.
• In more severe cases however, subjects must
  undergo occlusion therapy.
• The unaffected eye is patched to force the use of
  the previously deprived eye.

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Treatment of Amblyopia

• This should allow cortical connections to be
  re-established leading to improvements in spatial
  vision.
• Young children are averse to patching.
• Thus, children and parents are often not
  compliant.
• This makes it difficult for children to show
  visual improvement and for researchers to
  determine how effective patching is.

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Treatment of Amblyopia

• Full-time occlusion does not allow the formation
  of binocular cells.
• Patient is patched during most of the waking
  hours.
• As a result, good stereoacuity is unlikely.
• A better option may be part-time occlusion.
• Eg. The patient is patched two hours per day.
• This may allow for stereopsis.
• Patching can be done at home.
• This may not be appropriate for severe cases of
  amblyopia.

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Treatment of Amblyopia

• Another type of treatment is penalization.
• The unaffected eye is treated with a
  pharmacologic agent such as atropine.
• Prevents accommodation.
• A sharp image can not be formed on the retina.
• However, administration of eye drops in young
  children is very difficult.

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Treatment of Amblyopia

• A relatively new treatment is to provide the
  patient with levadopa.
• Levodopa (L-dopa) is the metabolic precursor of
  dopamine.
• L-dopa may re-establish a period of plasticity in
  the visual cortex.
• Allow cortical cells to be open for the formation
  of new connections.

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Treatment of Amblyopia

• There is evidence that L-dopa leads to visual
  improvements even in adults.
• It is not known whether these improvements are
  long-lasting.
• Also, L-Dopa may produce improvements in both
  eyes.
• There may be a persistent difference between the
  eyes.

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When is Treatment Effective?

• The success of treatment depends on three
  factors.
• The depth of amblyopia
• Patients with more severe amblyopia tend to show
  poorer outcomes.
• Rarely reach 20/20 or 20/25 in the amblyopic eye.

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When is Treatment Effective?

• Age of Onset
• Cases that exist early tend to show poorer
  outcomes.
• Duration of Deprivation
• The longer the deprivation, the poorer the
  outcome.

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When is Treatment Effective?

• The last two factors are closely linked.
• It appears that the duration of deprivation is
  the more important of the two.
• These last two factors indicate that the prompt,
  early detection of amblyopia is critical as early
  treatment leads to better outcomes.