What is amblyopia?
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 the poorer vision is called amblyopic. Usually, only one eye is affected by amblyopia, but it is possible for both eyes to be “lazy.”
The condition is common; approximately two or three out of every 100 people has amblyopia. The best time to correct amblyopia is during infancy or early childhood.
How does normal vision develop?
Newborn infants are able to see, but as they use their eyes during the first months of life, their vision improves. During early childhood years, their visual system changes quickly and their sight continues to develop.
If a child cannot use his or her eyes normally, vision does not develop properly and may even decrease. After the first nine years of life, the visual system is normally fully developed and usually cannot be changed.
In order to have normal vision, it is important that both eyes develop equal vision.
People with amblyopia in one eye are more than twice as likely to lose vision in the healthy eye from trauma. If the vision in one eye should be lost later in life from an accident or illness, it is essential that the other eye have normal vision. For these reasons, amblyopia must be detected and treated as early as possible.
When should vision be tested?
In addition to the well-baby exams that all babies should have as newborns and between ages 6 to 12 months, preschool-aged children should have eye exams between 3 and 4 years old.
Most doctors test vision as part of a child’s medical examination. They may refer a child to an ophthalmologist (Eye M.D.) if there is any sign of eye problems.
If there is a family history of misaligned eyes, childhood cataract or a serious eye disease, an ophthalmologist should examine the eyes during infancy.
What are the symptoms of amblyopia?
It is not easy to recognize amblyopia in children. A child may not be aware of having one strong eye and one weak eye. Unless the child has a misaligned eye or other condition that can be seen, there is often no way for parents to tell that something is wrong.
Some symptoms of amblyopia to look for in a child include:
- Poor vision in one eye or overall poor vision;
- Squinting, tilting the head or closing one eye to see;
- Poor depth perception (difficulty judging relative distances between objects);
- An inward- or outward-wandering eye;
Who is at risk for amblyopia?
The following factors can raise a child’s risk of having amblyopia:
- Having misaligned eyes (strabismus);
- Severe nearsightedness or farsightedness in both eyes;
- Unequal vision in both eyes (one eye more nearsighted or farsighted than the other);
- Having a condition that prevents light from entering the eye correctly, such as cataract or possibly a droopy eyelid;
- Family history of amblyopia or strabismus;
- Premature birth or low birth weight.
What causes amblyopia?
Amblyopia is caused by any condition that affects normal use of the eyes and visual development. In many cases, amblyopia may be hereditary, or passed down through the family. Amblyopia has three major causes:
Strabismus (misaligned eyes)
Amblyopia occurs most commonly with misaligned or crossed eyes. The crossed eye “turns off” to avoid double vision, and the child uses only the better eye. The misaligned eye then fails to develop good vision.
Unequal focus and refractive errors
Refractive errors are eye conditions that are corrected by wearing eyeglasses. Amblyopia occurs 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. The eyes can look normal, but one eye has poor vision. This is the most difficult type of amblyopia to detect since the child appears to have normal vision when both eyes are open.
Amblyopia can also occur in both eyes if both eyes have very blurred vision. This can happen when there is a high degree of nearsightedness, farsightedness, or astigmatism.
Cloudiness in the normally clear eye tissues
An eye disease such as a cataract (a clouding of the eye’s naturally clear lens) may lead to amblyopia. Any factor that prevents a clear image from being focused on the retina at the back of the eye can lead to the development of amblyopia in a child. This is often the most severe form of amblyopia.
How is amblyopia diagnosed?
It is not easy to recognize amblyopia. A child may not be aware of having one strong eye and one weak eye. Unless the child has a misaligned eye or other obvious abnormality, there is often no way for parents to tell that something is wrong.
Amblyopia is detected by finding a difference in vision between the two eyes or poor vision in both eyes. Since it is difficult to measure vision in young children, your ophthalmologist often estimates visual acuity by watching how well a baby follows objects with one eye when the other eye is covered.
Using a number of tests, the ophthalmologist watches how a baby reacts when one eye is covered. If one eye is amblyopic and the strong eye is covered, the baby may attempt to look around the patch, try to pull it off, or cry.
Poor vision in one eye does not always mean that a child has amblyopia. Vision can often be improved by prescribing eyeglasses for a child.
Your ophthalmologist will also carefully examine the inside of the eye to see if other eye diseases may be affecting vision. These diseases include:
- Inflammations (swelling);
- Tumors; and
- Other inner eye problems.
How is amblyopia treated?
To correct amblyopia, a child must be made to use the weak eye. This is usually done by covering or blurring the strong eye, often for weeks or months. Even after vision has been restored in the weaker eye, it may be necessary to continue patching the other eye part-time for a few more years to maintain the improvement.
Eyeglasses may be prescribed to correct focusing problems. If glasses alone do not improve vision, then patching is needed.
Amblyopia may also be treated by blurring the vision in the strong eye with special eyedrops or lenses to force the child to use the amblyopic eye.
Amblyopia is usually treated before surgery to correct misaligned eyes, and patching or blurring with eyedrops is often continued after surgery as well.
If your ophthalmologist finds a cataract or other problem in the eye, surgery may be required. An intraocular lens may be implanted. After surgery, eyeglasses or contact lenses can be used to restore focusing while patching improves vision.
Amblyopia usually cannot be cured by treating the cause alone. The weaker eye must be made stronger in order to see normally. Prescribing eyeglasses or performing surgery can correct the cause of amblyopia, but your ophthalmologist must also treat the amblyopia itself.
If amblyopia is not treated, several problems may occur:
- The amblyopic eye may develop a serious and permanent visual defect;
- Depth perception (seeing in three dimensions) may be lost, because good vision in both eyes is needed;
- If the stronger eye becomes diseased or injured, a lifetime of poor vision may result.
People who have good vision in only one eye may find they are limited in the kinds of jobs they can perform. Your ophthalmologist can teach you how amblyopia can be treated, and can help you and your child successfully carry out this treatment.
Children do not like to have their strong eye patched or blurred. As a parent, however, you should help your child to do what is best for him or her. Your interest, involvement and persistence is the key to ensuring your child’s amblyopia treatment succeeds.
Loss of vision is preventable
Success in the treatment of amblyopia also depends upon:
- How severe the amblyopia is; and
- How old the child is when treatment is begun.
If the problem is found and treated early, vision can improve for most children. Amblyopia caused by strabismus or unequal refractive errors may be treated successfully during the first nine years of age, and usually won’t occur again.
If amblyopia is not detected until after early childhood, treatment may not be successful. Amblyopia caused by cloudiness of the eye tissue needs to be found and treated extremely early — within the first few months of life — in order to be treated successfully.
If you have questions or would like more information, talk with an ophthalmologist from Beach Eye Medical Group!