Definition | Symptoms | Treatment | Clinic Information
Definition
Amblyopia, sometimes called a "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 but must develop it between birth and 6-9 years of age by using each eye regularly with 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(s) said to be amblyopic. This common condition, affecting up to 4% of all children, should be diagnosed and treated during infancy or early childhood to obtain optimum 3-dimensional vision and to prevent permanent vision loss. Once a child is 6-9 years old, diagnosis and/or treatment will no longer result in vision improvement.
Amblyopia has three major causes: strabismus, unequal refractive error or anisometropia, and reduced clarity or obstruction of the optical structures in the eye, e.g., cornea, lens, and vitreous gel.
Misaligned eyes (strabismus) is the most common cause of amblyopia. When both eyes are not aimed in exactly 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 eye — the dominant eye. If this persists for a period 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) is an eye condition in which each eye has a different refractive error and therefore both eyes cannot be in focus at the same time. Amblyopia occurs when one eye (usually the eye with the greater refractive error) is out of focus because it is more nearsighted, farsighted or astigmatic than the other. Again, the brain "turns off" the image from the unfocused eye, and this eye will not develop normal vision. Because the eyes often look normal, this can be the most difficult type of amblyopia to detect and requires careful vision screening of acuity measurements by an eye doctor at an early age. Treatment with glasses or contact lenses to correct the refractive error of both eyes, sometimes with part-time patching of the better seeing eye, is necessary in early childhood to correct the problem.
Obstruction of or cloudiness (deprivation) in the normally clear eye tissues may also 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 getting a clear image on the retina are a cataract or cloudy lens inside the eye, a cloudy cornea at the front of the eye, or a droopy eyelid or eyelid tumor.
It is not easy to recognize amblyopia. A child may not be aware of having one normal eye and one with 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 or trained vision screener 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 will also 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.- Decreased vision
- Misaligned eyes
Treatment
To correct amblyopia, a child must be encouraged to use the weaker eye. This is usually accomplished by patching or covering the stronger eye. Patching will often continue for weeks, months, or even years in order to restore normal 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 or lenses to force the child to use the amblyopic eye.
Amblyopia is sometimes treated before or at the same time as surgery to correct misaligned eyes, remove a cataract, or correct another ocular abnormality. In some cases, cataract surgery or glaucoma surgery might be necessary to treat deprivation amblyopia. Patching may be required even after surgery to improve vision, and glasses or contact lenses may be required to restore appropriate focusing.
It is very important that you and your child fully carry out any treatment prescribed by your ophthalmologist. Children do not like to have their eyes patched, or eye drops instilled, especially since they have been depending on the patched eye to see clearly and it will seem to them as though you are blinding them. 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 remember, with initial consistent therapy the vision in the amblyopic eye will improve and the treatment will become easier.
If the amblyopia is not treated early, during the period of vision development between birth and 6-9 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 resulting handicap, e.g., inability to drive or work, may be the result.
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.
Clinic Information
For more information, see the Comprehensive Ophthalmology Clinics and the complete Clinic Services listing of the U-M Kellogg Eye Center.
