Amblyopia, also known as "lazy eye," is a condition characterized by diminished vision in one eye. It is not correctable by eyeglasses or contact lenses and is not usually triggered by an eye disease. Instead, amblyopia can develop when the extraocular muscles fail to align the eyes properly and the part of the brain that controls vision "favors" one eye over the other. If you have one eye with a significant refractive error compared to the other and this one goes uncorrected for a period of time; or if there is a large difference in their refractive power and one eye is favored, your condition will worsen.
All babies are born with poor eyesight that normally improves as they grow. In amblyopia, one eye becomes stronger. If the weaker eye is untreated, eyesight will progressively worsen. Amblyopia is the most common cause of visual impairment restricted to one eye in children and young to middle-aged adults. About 5% of children in the United States have amblyopia.
The two most common types of amblyopia are strabismic and anisometropic. In strabismic amblyopia, strabismus is present and the eyes are not aligned properly resulting in one eye being used less than the other. The non-preferred eye is not adequately stimulated and the visual brain cells do not develop normally. With anisometropic amblyopia, the eyes have different refractive powers. For example, one of your eyes may be nearsighted and the other farsighted. It may be difficult for your brain to balance the difference and it favors the stronger eye.
Anything that interferes with equal development of vision in both eyes between birth and about six years can result in amblyopia. Strabismus and anisomtreopia are the most common causes of amblyopia. Other risk factors include congenital cataracts, something that blocks the cornea or lens, and a droopy eyelid that obstructs the field of vision in one eye.
Amblyopia may not produce symptoms that are obvious to a parent or the affected child. Amblyopia caused by an undetected refractive error may go unnoticed for years, due to the fact that one of the eyes is functioning normally. As a result, many children remain unaware of vision problems, especially before they begin school. The condition is often diagnosed during the first eye examination at a later age, when improvement in vision to its fullest potential may no longer be possible. However, sometimes a child may squint or close one eye, which indicates a visual problem. A child old enough to verbalize may complain of headaches or eyestrain.
A diagnosis of amblyopia is made with a complete eye examination including a physical exam of the eye, a medical history, and a vision test. An optometrist or an ophthalmologist can perform the examination. A basic eye exam usually begins with a medical history and questions about the patient’s health and past and current eye problems. As a parent of an infant or young child, you will be the one to answer these questions. Your children may be able to specify if they have problems seeing out of one eye, or if they have problems reading or seeing the blackboard.
Eye movement is tested by moving a light or object through the patient’s field of vision and assessing the eye’s ability to follow it. This allows the doctor to determine if the eye muscles are working properly. Tests that access binocular vision, how the eyes work together, are also done. In strabismus, the stronger eye may do all the looking, or the weaker eye may align itself intermittently. If the patient is old enough, a vision test involving reading letters from an eye chart may also be utilized. This helps determine if either eye has a refractive error. If the patient is not old enough to know letters, other objective methods are used to determine the refractive error. Other tests may be performed if disease is the suspected cause. These tests depend on the results of the initial exam, symptoms, and the appearance of the eye.
Your treatment depends on the underlying cause and how early the condition is diagnosed. It was previously believed that only young children could benefit from treatment, because the brain’s vision system is completely developed by age eight to ten. Detection and correction before the age of two offers the best chance for normal vision. However, current research has concluded that effective treatment can take place at any age. The longer the condition goes uncorrected, the longer the length of treatment required. Your treatment can be as simple as a pair of eyeglasses or as complex as surgery.
Surgery is used to treat amblyopia caused by strabismus, cataracts, and other blockages on the cornea. For strabismus, surgery is performed on the eye muscle to force the eyes into alignment. Sometimes surgical results are cosmetic; the eyes look straighter, but they are still not aligned and require further treatment. Early surgery is often recommended, so that infants can develop normal sight as their eyes mature.
Eyeglasses are used to correct the visual imbalance if amblyopia is caused by a refractive error. Glasses or bifocals are also sometimes used to straighten strabismic eyes. Vision therapy uses exercises to strengthen the eye muscle and help both eyes work together. It also trains the brain to use the amblyopic eye, improving its vision. Vision therapy can be used alone, before or after surgery, and with eyeglasses.
Patching involves covering the good eye and forcing use of the amblyopic eye. The weaker eye becomes stronger with use. The problem with eye patches is that some children do not like wearing them. A patch can be worn all day or for a few hours a day, depending on the child’s age and vision. It is used until the eye has strengthened and vision has normalized or until improvement plateaus.
Amblyopia may be caused by other eye conditions, so diagnosing and treating visual problems as early as possible can prevent its onset. An initial eye examination is recommended at age three to six months and then periodically thereafter. An eye problem detected in infancy, such as strabismus, can be corrected before it causes amblyopia.
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