Practice Essentials
Amblyopia, or lazy eye, refers to a unilateral or bilateral decrease of vision, in one or both eyes, caused by abnormal vision development in childhood or infancy. It is a common vision problem in children and is the leading cause of decreased vision among children. Most vision loss is preventable or reversible with the right kind of intervention.
Signs and symptoms
The history should address the following:
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Previous history of patching or eye drops
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Past compliance with these therapies
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Previous ocular surgery or disease
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Family history of strabismus or other ocular problems
The physical examination should include the following:
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Assessment of visual acuity
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Testing for crowding phenomenon (difficulty in distinguishing optotypes that are close together)
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Specific testing measures in preverbal children
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Evaluation of contrast sensitivity
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Neutral density filter testing
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Assessment of binocular function
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Detection of eccentric fixation
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Cycloplegic refraction
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Sensory testing
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Motility examination
A full eye examination must be performed to rule out ocular pathology.
The most important causes of amblyopia are as follows [1, 2] :
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Anisometropia or refractive errors
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Strabismus
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Strabismic anisometropia
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Visual deprivation
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Organic lesions
See Clinical Presentation for more detail.
Diagnosis
Imaging studies that may be helpful when the ocular examination is normal and/or there is suspicion of an organic cause not detected on the ocular examination include the following:
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CT
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MRI
Other tests that may be helpful if an organic cause is suspected include the following:
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Spectral-domain optical coherence tomography (SD-OCT) [3]
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Electrophysiologic studies (investigational; differences noted are controversial)
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Fluorescein angiography (to assess the retina)
See Workup for more detail.
Management
First, rule out an organic cause and treat any obstacle to vision, such as cataract or ptosis, if clinically significant. Next, treat anisometropia and refractive errors. Occlusion or penalization therapy (to force the use of the amblyopia eye) are generally considered the first treatment options for amblyopia.
Occlusion therapy
The following are general guidelines for occlusion therapy:
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Patching may be full-time or part-time
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Always consider lack of compliance in a child when visual acuity is not improving. Question patients regarding peeking
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In addition to adhesive Band-Aid–type patches, consider the use of opaque contact lenses, occluders mounted on spectacles, and adhesive tape or Bangerter foils on glasses
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Establishing whether the vision of the better eye has been degraded sufficiently with the chosen therapy
Atropine penalization therapy
The following are general guidelines for atropine penalization therapy:
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Atropine eye drops are placed in the sound eye
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Establish whether the vision of the better eye has been degraded sufficiently with the chosen therapy
Other treatment
Additional treatment options include the following:
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Optical blurring through contact lenses or elevated bifocal segments
Treatment of strabismus generally occurs last. The optimal endpoint of strabismic amblyopia is freely alternating fixation with equal vision. Surgery generally is performed when this endpoint has been reached.
See Treatment and Medication for more detail.
Background
Amblyopia refers to a decrease of vision, either unilaterally or bilaterally, for which no cause can be found by physical examination of the eye. Organic amblyopia refers to irreversible amblyopia caused by ocular pathology that will limit vision improvement. [1, 2, 4]
Most vision loss from amblyopia is preventable or reversible with the right kind of intervention. The recovery of vision depends on how mature the visual connections are, the length of deprivation, and at what age the therapy is begun. It is important to rule out any organic cause of decreased vision because some diseases may not be easily detectable on routine examination.
Pathophysiology
Although many types of amblyopia exist, it is believed that their basic mechanisms are the same even though each factor may contribute different amounts to each specific type of amblyopia. In general, amblyopia is believed to result from disuse from inadequate foveal or peripheral retinal stimulation and/or abnormal binocular interaction that causes different visual input from the foveae. [5]
Three critical periods of human visual acuity development have been determined. [6, 7] During these time periods, vision can be affected by the various mechanisms to cause or reverse amblyopia. These periods are as follows:
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The development of visual acuity from the 20/200 range to 20/20, which occurs from birth to age 3-5 years.
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The period of the highest risk of deprivation amblyopia, from a few months to 7 or 8 years.
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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.
Whether different visual functions (eg, contrast sensitivity, stereopsis) have different critical periods is not known. In the future, determination of these time frames may help modify treatment of amblyopia.
Frequency
United States
Prevalence of amblyopia is difficult to assess and varies in the literature, ranging from 1-3.5% in healthy children to 4-5.3% in children with ophthalmic problems. Most data show that about 2% of the general population has amblyopia.
Amblyopia was shown in the Visual Acuity Impairment Survey sponsored by the National Eye Institute (NEI) to be the leading cause of monocular vision loss in adults aged 20-70 years or older. Prevalence of amblyopia has not changed much over the years.
Mortality/Morbidity
Amblyopia is an important socioeconomic problem. Studies have shown that it is the number one cause of monocular vision loss in adults. Furthermore, persons with amblyopia have a higher risk of becoming blind because of potential loss to the sound eye from other causes.
Race
No racial preference is known.
Sex
No gender preference is known.
Age
Amblyopia occurs during the critical periods of visual development. An increased risk exists in those children who are developmentally delayed, were premature, and/or have a positive family history.
Prognosis
After 1 year, about 73% of patients show success after their first trial of occlusion therapy. Studies have shown that the number of patients who retain their level of visual acuity decreases over time to 53% after 3 years.
Risk factors for failure in amblyopia treatment include the following:
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Type of amblyopia: Patients with high anisometropia and patients with organic pathology have the worst prognosis. Patients with strabismic amblyopia have the best outcome.
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Age at which therapy began: Younger patients seem to do better.
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Depth of amblyopia at start of therapy: The better the initial visual acuity in the amblyopic eye, the better the prognosis.
A study by Mirabella et al determined that even with successful treatment of an amblyopic eye, perception of images in real-world scenes remains altered in patients with a history of amblyopia. [33]
Patient Education
Parents need to be educated about the importance of treatment and compliance as well as the visual implications because the treatment of amblyopia often lies in the hands of the parents.
For excellent patient education resources, visit eMedicineHealth's Eye and Vision Center. Also, see eMedicineHealth's patient education article How to Instill Your Eyedrops.
