Amblyopia
What is Amblyopia (Lazy Eye)
Amblyopia refers to a decrease of vision, either unilaterally or bilaterally, for which no cause can be found by physical examination of the eye
2%–4% of U.S. population affected
Amblyopia
Three critical periods of human visual acuity development have been determined. During these time periods, vision can be affected by the various mechanisms to cause or reverse amblyopia. These periods are as follows:
- The development of visual acuity from the 20/200 range to 20/20, which occurs from birth to age 3-5 years.
- The period of the highest risk of deprivation amblyopia, from a few months to 7 or 8 years.
- The period during which recovery from amblyopia can be obtained, from the time of deprivation up to the teenage years or even sometimes the adult years.
Amblyopia
Diagnosis of amblyopia usually requires a 2-line difference of visual acuity between the eyes
Causes of Amblyopia
Many causes of amblyopia exist; the most important causes are as follows:
Anisometropia
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Inhibition of the fovea occurs to eliminate the abnormal binocular interaction caused by one defocused image and one focused image.
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This type of amblyopia is more common in patients with anisohypermetropia than anisomyopia. Small amounts of hyperopic anisometropia, such as 1-2 diopters, can induce amblyopia. In myopia, mild myopic anisometropia up to -3.00 diopters usually does not cause amblyopia.
Strabismus
The patient favors fixation strongly with one eye and does not alternate fixation. This leads to inhibition of visual input to the retinocortical pathways.
Incidence of amblyopia is greater in esotropic patients than in exotropic patients
Alternation with alternate suppression avoids amblyopia
Visual Deprivation
Amblyopia results from disuse or understimulation of the retina. This condition may be unilateral or bilateral. Examples include cataracts, corneal opacities, ptosis, and surgical lid closure
Deprivation Amblyopia
Bilateral Deprivation Amblyopia
Organic
- Structural abnormalities of the retina or the optic nerve may be present.
- Functional amblyopia may be superimposed on the organic visual loss
Ametropic Amblyopia
Uncorrected high hyperopia is an example of this bilateral amblyopia.
Screening: Importance
- Amblyopia is usually preventable or treatable
- Early detection is key to effective treatment
- Life-threatening disorders may present as amblyopia
- Screening responsibility rests with the primary care physician
Amblyopia: Early Detection
- Assess red reflex
- Determine visual acuity
- Evaluate ocular alignment
Direct Ophthalmoscope
Direct Ophthalmoscope: Assessing Red Reflex
Direct Ophthalmoscope: Examining Retina
Normal Red Reflex
Asymmetric Red Reflex
Treatment
The clinician must first rule out an organic cause and treat any obstacle to vision (eg, cataract, occlusion of the eye from other etiologies).
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Remove cataracts in the first 2 months of life, and aphakic correction must occur quickly
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Treatment of anisometropia and refractive errors must occur next
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The next step is forcing the use of the amblyopic eye by occlusion therapy
