What Is It?
Amblyopia is poor vision in an eye that did not develop normal sight during early childhood. It is sometimes called “lazy eye”. When one eye develops good vision while the other does not, the eye with poorer vision is called amblyopic. Usually only one eye is affected by amblyopia.
The condition is common, affecting approximately 4 out of every 100 people. Amblyopia can be corrected only if treated during infancy or early childhood. Parents must be alert to this visual threat if their child is to see properly later in life.
Most physicians test vision as part of a child’s medical examination. However, they may refer a child to an ophthalmologist if there is difficulty in measuring vision or any sign of amblyopia or related conditions. It is recommended that all children have their vision checked by their pediatrician, family physician or ophthalmologist at of before age three.
New techniques have been developed which make it possible to test vision in infants and young children. If there is a family history of misaligned eyes, childhood cataracts or other family history of serious eye disease, vision can be checked even earlier than age three.
The Development of Normal Vision
Although newborn infants are able to see, vision improves over the first months of life as use of the eyes increases. During early childhood years, the visual system remains in a changeable state.
Vision continues to develop with proper use of the eyes. However, if the eyes are not used to capacity, vision does not develop properly and may even decrease. In most cases, after the first nine years of life, development of the visual system is complete and cannot be changed.
The development of equal vision in both eyes is necessary for an entirely normal visual life. Many occupations are not open to individuals who have good vision in one eye only. Furthermore, should the vision in one eye be lost later in life from an accident or illness, it is essential that the other eye have normal vision. Amblyopia must be detected and treated as early as possible.
Causes and Symptoms
Amblyopia is caused by any condition that affects normal use of the eyes and visual development. Amblyopia has three major causes:
- Strabismus (misaligned eyes)
- Unequal focus (refractive error)
- Cloudiness in the normally clear eye tissues.
Amblyopia occurs most commonly with misaligned eyes such as crossed eyes. The crossed eye “turns off” to avoid double vision, becomes lazy or amblyopic, and the child prefers the better eye. Amblyopia may also occur when one eye is out of focus because it is more nearsighted, farsighted or astigmatic than the other. The unfocused (blurred) eye “turns off” and becomes amblyopic. Sometimes, in these cases the eyes can look normal but one eye has poor vision. This is the most difficult type of amblyopia to detect and requires careful measurement of vision.
An eye disease such as a cataract (a clouding of the lens which prevents light from being focused properly by the eye), may lead to amblyopia. Any factor that prevents a clear image from being focused inside the eye can lead to the development of amblyopia in a child.
Children may also inherit conditions from parents that cause amblyopia. Children in a family with a history of amblyopia or misaligned eyes should be checked by an ophthalmologist early in life.
It is important to realize that treating the condition that causes amblyopia does not cure the amblyopia itself. The ophthalmologist must treat amblyopia separately before correcting the blurred vision with glasses, removing a cataract or straightening the misdirected eyes.
Amblyopia often goes unrecognized. A child may not be aware of having one good eye and one poor eye. Unless the amblyopic child has a misaligned eye or other obvious abnormality, there is nothing to suggest the child’s condition to the parents.
Detection and Diagnosis
Amblyopia is detected by finding a difference in vision between each eye. Since measurement of vision is difficult in young children, the ophthalmologist often estimates visual acuity by watching how well a baby follows objects with each eye when the other eye is covered.
Using a variety of tests, the ophthalmologist observes the responses of the baby when one eye is covered. If one eye is amblyopic and the good eye is covered, the baby may attempt to look around the patch placed over the good eye or object to the patch.
Poor vision in one eye does not always mean amblyopia is present. Vision can often be improved with the prescription of glasses. However, the ophthalmologist will also carefully examine the interior of the eye to see if eye disease such as cataracts, inflammations, tumors or other disorders of the inner eye may be causing decreased vision.
To correct amblyopia, the child must be forced to use the lazy eye. This is usually done by patching or covering the good eye, often for weeks or months. Part-time patching may be required over a period of years to maintain improvement even after vision has been restored.
Glasses may be prescribed to correct errors or imbalance in focusing. If glasses alone do not improve vision, then patching is necessary. Occasionally, amblyopia is treated by blurring the vision in the good eye with special eye drops or optical lenses to force the child to use the amblyopic eye.
If an abnormality such as a cataract is discovered, surgery is required to correct the problem causing the amblyopia. After surgery, glasses, contact lenses or other methods can be used to restore focusing along with patching to improve vision. Amblyopia usually is treated prior to surgery for misaligned eyes and is frequently needed after surgery as well.
If amblyopia is not treated, several things may occur:
- The amblyopic eye may develop a serious and irreversible visual defect
- Depth perception may be lost
- If the good eye becomes diseased or injured, a lifetime of poor and uncorrectable vision may be the result
The ophthalmologist can instruct parents about how to treat amblyopia, but it is a parental responsibility to carry out this treatment. No child likes to have a good eye patched, but parents must convince their child to do what will be best for them.
Successful treatment mostly depends on parental interest and involvement, and their ability to gain their child’s cooperation. In most cases, it is the parent’s who play an important role in determining whether their child’s amblyopia is to be corrected.
Loss of Vision is Largely Preventable
Successful treatment depends upon how severe the amblyopia is and the age of the child when treatment is begun. If the problem is detected and treated early, most amblyopic children will develop improved vision, but prolonged part-time treatment may be necessary until the child is about nine years of age. After this time, amblyopia does not return.
If amblyopia is first discovered after the child is eight to nine years of age, treatment may not be successful. Visual loss due to strabismus or unequal refractive errors may be treated successfully with patching at a much older age than the amblyopia caused by opacities in the eye.