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Psychology 4051

Psychology 4051. Amblyopia. 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 or more (i.e., 0.2 logMAR) on a visual acuity test.

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Psychology 4051

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  1. Psychology 4051 Amblyopia

  2. 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 or more (i.e., 0.2 logMAR) on a visual acuity test. • While wearing best correction.

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

  4. 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

  5. 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.

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Treatment of Amblyopia • Accommodative esotropia is treated with glasses

  15. 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.

  16. Treatment of Amblyopia • Severe ptosis can be treated surgically.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  21. 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.

  22. 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.

  23. 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.

  24. 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.

  25. 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.

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