Lazy eye (Amblyopia) is poor vision in an eye that did not develop normal sight during early childhood. 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 lazy eye. The condition is common, affecting approximately 2 or 3 out of every 100 people. The best time to correct lazy eye 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, vision improves. During early childhood years, the visual system changes quickly and vision 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 usually fully developed and usually cannot be changed. The development of equal vision in both eyes is necessary for normal vision. Many occupations are not open to people who have good vision in one eye only.
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. Without normal vision in at least one eye, a person is visually impaired. Tests can determine if you need treatment for lazy eye.
When should vision be tested?
It is recommended that all children have their vision checked at or before their fourth birthday. Most physicians test vision as part of a child’s medical examination. They may refer a child to an ophthalmologist if there is any sign of an eye condition. New techniques make it possible to test vision in infants and young children. If there is a family history of misaligned eyes, childhood cataracts or a serious eye disease, an ophthalmologist can check vision even earlier than age three.
What causes lazy eye?
Lazy eye is caused by any condition that affects normal use of the eyes and visual development. In many case, the conditions associated with lazy eye may be inherited. Children in a family with a history of lazy eye or misaligned eyes should be checked by an ophthalmologist early in life.
Lazy eye has three major causes:
- Strabismus (misaligned eyes) Lazy eye 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.
- Unequal forces (Refractive error) Refractive errors are eye conditions that are corrected by wearing glasses. Lazy eye 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 lazy eye to detect since it requires careful measurement of vision.
- Cloudiness in the normally clear eye tissues An eye disease such as a cataract (clouding of the eye’s natural lens) may lead to lazy eye. Any factor that prevents a clear image from being focused inside the eye can lead to the development of lazy eye in a child. This is often the most severe form of lazy eye.
How is lazy eye diagnosed?
It is not easy to recognize lazy eye. 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. Lazy eye is detected by finding a difference in vision between the two 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 variety of tests, the ophthalmologist observes the reactions 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, try to pull it off or cry. Poor vision in one eye does not always mean that a child has lazy eye. Vision can often be improved by prescribing glasses for a child.
Your ophthalmologist will also carefully examine the interior of the eye to see if other eye diseases may be causing decreased vision. These diseases include:
- Other disorders of the inner eye
How is lazy eye treated?
To correct lazy eye, a child must be made to use the weak eye. This is usually done by patching or covering the strong eye, often for weeks or months. Even after vision has been restored in the weak eye, part-time patching may be required over a period of years to maintain the improvement.
Glasses may be prescribed to correct errors in focusing. If glasses alone do not improve vision, then patching is necessary. Occasionally, lazy eye 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.
Lazy eye is usually treated before surgery to correct misaligned eyes, and patching is often continued after surgery as well. If a cataract or other abnormality is found, surgery may be required to correct the problem. An intraocular lens may be implanted. After surgery, glasses or contact lenses can be used to restore focusing, while patching improves vision.
Lazy eye cannot usually be cured by treating the cause alone. The weaker eye must be made stronger in order to see normally. Prescribing glasses or performing surgery can correct the cause of lazy eye, but your ophthalmologist must also treat the lazy eye.
If lazy eye 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
- If the good eye becomes diseased or injured, a lifetime of poor vision may be the result.
Your ophthalmologist can give you instructions on how to treat lazy eye, but it is up to you and your child to carry out this treatment. Children do not like to have their eyes patched, especially if they have been depending on the eye being patched to see clearly. But as a parent, you must convince your child to do what is best for him or her. Successful treatment mostly depends on your interest and involvement, as well as your ability to gain your child’s cooperation. In most cases, parents play an important role in determining whether their child’s’ lazy eye is to be corrected.
Loss of vision is preventable. Success in the treatment of lazy eye also depends upon:
- How severe the lazy eye is
- How old the child is when treatment is begun
If the problem is detected and treated early, vision can improve for most children. Sometimes part-time treatment may have to continue until the child is about nine years of age. After this time, lazy eye usually does not recur. If lazy eye is first discovered after early childhood, treatment may not be successful. Lazy eye caused by strabismus or unequal refractive errors may be treated successfully at a much older age than the lazy eye caused by cloudiness in tissues in the eye.
If you have additional questions or would like any further information, contact your ophthalmologist.