What Is Amblyopia?
Amblyopia, sometimes referred to as "lazy eye," occurs when one or both eyes do not develop normal vision during early childhood. Babies are not born with 20/20 vision in each eye. Instead, they must develop it between birth and 6 to 9 years of age by regularly using each eye, an identical focused image falling on the retina of each eye. If this does not occur in one or both eyes, vision will not develop properly. Instead, vision will be reduced and the affected eye becomes amblyopic. This common condition, affecting up to 4 percent of all children, must be diagnosed and treated as early as possible during infancy or early childhood to prevent permanent vision loss and to allow for development of optimal stereo or 3-dimensional vision. After the age of approximately 6 to 9 years, diagnosis and/or treatment may no longer result in vision improvement.
- Decreased vision in one or both eyes
- Strabismus (misaligned eyes)
- Poor depth perception
The symptoms described above may not necessarily mean that your child has amblyopia. However, if you observe one or more of these symptoms, contact your child's ophthalmologist for a complete exam.
- Misaligned eyes (strabismus)
Eye misalignment is the most common cause of amblyopia. When both eyes are not aimed in the same direction, the developing brain "turns off" the image from the misaligned eye to avoid double vision and the child uses only the better, or dominant, eye. If this persists for any period of time, even as short as a few weeks, the eye will not connect properly to the visual cortex of the brain and amblyopia will result.
- Unequal refractive error (anisometropia)
If the refractive error of each eye is not the same then both eyes cannot be in focus at the same time. Amblyopia occurs when one eye (usually the eye with the greater refractive error) remains out of focus because it is more nearsighted, farsighted, or astigmatic than the other, which becomes the dominant seeing eye. This results in disuse of the unfocused eye, which fails to connect properly to the brain and will not develop normal vision. Because both eyes in children with anisometropia often look normal, this can be the most difficult type of amblyopia to detect. It requires careful evaluation of visual acuity and ocular preference in infants and young children by a primary care physician or ophthalmologist as part of a vision screening evaluation at 6 months and 3 years of age and preschool. Treatment with glasses or contact lenses to properly correct the refractive error of each eye, sometimes with part-time patching of the better-seeing eye, is necessary in early childhood to correct the problem.
- Obstruction or cloudiness of the visual system (deprivation)
Obstruction or cloudiness in the normally clear eye tissues also may lead to amblyopia. Any disorder that prevents a clear image from being focused inside the eye can block the formation of a clear image on the retina and lead to the development of amblyopia in a child. This often results in the most severe form of amblyopia. Examples of disorders that can interfere with projecting a clear image on the retina are a cataract or cloudy lens inside the eye, a cloudy cornea at the front of the eye, a droopy eyelid (ptosis) or eyelid tumor.
It is not easy to recognize amblyopia. Unlike adults, a child is usually unaware if one of his/her eyes has reduced vision. Unless the child has a misaligned eye or other obvious external abnormality, there is often no way for parents to tell that something is wrong. In addition, it is difficult to measure vision in very young children at an age in which treatment is most effective. Your ophthalmologist knows how to estimate visual acuity in an infant by watching how well a baby follows an object with one eye when the other eye is covered. He or she also will carefully examine the refractive error and optical clarity of the interior of the eye to see if other eye disorders such as cataract, glaucoma, tumor, or inflammation inside the eye may be causing decreased vision and lead to amblyopia.
- Positive family history of strabismus (misaligned eyes), amblyopia, childhood cataract or glaucoma
- Some genetic disorders that affect the eyes
- Pediatric cataracts or glaucoma
- Droopy eyelid (ptosis)
- Eyelid tumor that blocks the pupil
Tests and Diagnosis
- Visual acuity measurement in each eye and both eyes together (age appropriate)
- Cycloplegic refraction (with dilating eye drops)
- External or slit lamp exam
- Fundus (retina) examination
- Complete eye exam (age appropriate)
Treatment and Drugs
To correct amblyopia, a child must be forced to use the weaker eye. This usually is accomplished by correcting any abnormalities of the amblyopic eye (refractive error, visual opacities, retinal problems, etc.) to improve the vision potential in the ignored or amblyopic eye, and by patching (covering) or otherwise temporarily reducing the vision of the stronger eye (penalization). Some part-time patching will often be required for weeks, months, or even years in order to restore the best possible vision and maintain the improvement in the amblyopic eye. Glasses may be prescribed to correct refractive errors in one or both eyes. Occasionally, amblyopia is treated by blurring the vision in the good eye with special eye drops (atropine) or lenses to force the child to use the amblyopic eye.
Amblyopia sometimes is treated with glasses, patching or eye drops before or at the same time as surgery to correct misaligned eyes, remove a cataract, or correct another ocular abnormality. In some cases, cataract, glaucoma, or lid surgery may be necessary to treat deprivation amblyopia. Patching may be required even after surgery to improve vision; glasses or contact lenses may be required to restore appropriate focusing.
It is very important that you and your child fully comply with the treatment prescribed by your ophthalmologist. Children typically do not like to have their good eye patched, wear corrective lenses, or receive eye drops. And, since they have become dependent on their “good” eye to see clearly, they often feel as though you are blinding them when you patch or blur the unaffected eye. But, as a parent, you must convince your child to do what is best for his/her future vision because successful treatment depends on it. And, with initial consistent therapy, the vision in the amblyopic eye will improve and the treatment will become easier.
If amblyopia is not treated early, specifically during the period of visual development between birth and 6 to 9 years of age, it can result in a permanent visual defect or loss of depth perception. Then, later in life, if the “good” eye becomes diseased or injured, a lifetime of poor vision with a resulting handicap (the inability to drive or work) may occur.
If the problem is detected and treated early, vision will improve for most children. Sometimes part-time treatment may have to continue until the child is 6 to 9 years of age and vision development is complete. After this time, amblyopia usually does not return.
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Reviewed by Monte A. Del Monte, M.D.