Amblyopia is decreased vision in a normal appearing eye and is sometimes called a “lazy eye.” Usually only one eye is affected, but it is possible for both eyes to develop amblyopia. It occurs in early childhood and can be caused by misalignment of the eyes or poor vision due to another cause. The resulting decrease in vision may be slight (2 lines on the eye chart, such as 20/20 and 20/30) or profound (20/20 in one eye and 20/200 in the fellow eye.) Amblyopia is present in 3% of the American population.
Visual maturity occurs by about the age of 10 years. After this time amblyopia will not develop. The converse is also true. Amblyopia, when it is present, can only be treated until a child is about 10 years old. The child will generally keep the amount of vision which is achieved by the tenth birthday. This is why it is important to detect and treat amblyopia when children are young and the visual system is immature but capable of improvement.
There are several types of amblyopia: strabismic, anisometropic, and deprivation.
Strabismic amblyopia occurs due to a misalignment of the eyes. The brain detects double vision because both eyes are not looking at the same object. The visually immature brain suppresses or ignores the second image to reduce confusion. This gets rid of the double vision but it leads to a loss of vision in the deviating eye. The degree of amblyopia caused has no correlation with the degree of deviation of the eye. Even very small deviations can cause profound vision loss.
Anisometropic amblyopia occurs due to a difference in refractive error between the two eyes. Refractive errors are conditions that are corrected by wearing glasses: nearsighted (myopia), farsighted (hyperopia), and astigmatism. One eye generally has a clear image and the other a blurry image (usually the more farsighted eye). The brain chooses the clear image and suppresses or “turns off” the blurry image, leading to a loss of vision in that eye. The eyes look normal, but one has poor vision. If both eyes have a high amount of nearsightedness, farsightedness, or astigmatism, amblyopia can occur in both eyes.
Deprivation amblyopia occurs if vision is absent or reduced during the first few months of life. This is a critical period for visual development. Visual deprivation later in childhood can also cause amblyopia with severity related to the age of onset and the severity of deprivation. The most common cause of deprivation amblyopia is a cataract that is present at birth. Other causes include corneal scars or a profoundly drooping eyelid.
Treatment begins with correcting refractive errors to ensure that a sharp retinal image is presented to the brain by both eyes at all times. This requires the child to wear the appropriate glasses all waking hours.
In cases of strabismic amblyopia or deprivation amblyopia, surgery may be necessary to align the eyes or remove a cataract or scar tissue. Amblyopia usually is not cured with glasses alone and often requires treatment to make the poorer seeing eye stronger.
Once focusing errors have been corrected, the better seeing eye is covered or patched to force the child to use the poorer seeing eye. This treatment forces the brain to reverse the amblyopia. Before the age of ten, the brain is plastic and this treatment results in improvement in the ability of the neglected eye to see. The schedule of occlusion will vary during the treatment depending on the child’s age, the degree of amblyopia and the response to treatment. Occlusion can vary from all waking hours to as little as 2 hours a day. Patching must be monitored carefully since excessive patching of the good eye can cause deprivation amblyopia to develop in that eye. Appropriate follow-up is vital for this reason. Sometimes, drops that dilate the pupil of the better seeing eye can be used to penalize the sight in that eye and treat amblyopia.
Not all children will have a recovery to 20/20 vision. However, most children do have a significant improvement. In some children, for reasons which are not understood, the visual acuity cannot be made to improve beyond a certain level. This is more common in children where treatment was instituted late in childhood or where compliance with patching was a problem. Part-time patching may be needed for years to maintain the initial improvement.
If amblyopia is not treated, the affected eye will develop a permanent visual defect and depth perception (seeing in 3 dimensions) will be decreased. Children do not like having their good eye patched. They cannot see as well, especially if they have severe amblyopia. The patch may be irritating. The child may be very conscious of the cosmetic appearance of wearing the patch.
As a parent, you need to help your child to do what is in their ultimate best interest. Some occupations are closed to people who have good vision in only one eye. If your child were to be injured or develop a disease in the good eye, a lifetime of poor vision is the result. Your active involvement and persistence are critical to the successful treatment of your child’s amblyopia.
* Do not place patches over eyeglasses because they can be “peeked” over. Even small periods of cheating will undo hours of patching treatment.
* Patches may occasionally cause the skin to break down. If this happens, rotate the patch or trim it. If necessary, discontinue the patch for a day or two to allow the skin to heal.
* Compliance with patching can be difficult. In fact, most children will eventually engage their parents in the “battle of the patch”. Tricks for getting your children to accept the patch include:
o Make wearing the patch into a game. Decorate the patch each day. Have an adult also wear the patch (other children in the family who under 8 years of age should not wear a patch as this can interfere with their visual development).
o Provide simple rewards for wearing the patch. Place stickers on a calendar for each day that the child wears the patch as instructed. After a set number of days of compliance (such as 1 week), the child should receive a special treat. This does not need to be a toy. It could be a special privilege such as TV time or a visit to a special restaurant or receiving a favorite desert
o If your child naps, try putting the patch on while he is asleep. If he wakes up with the patch on, he may accept its presence.
o In infants, mittens may keep the child from removing the patch. Tubes placed over the arms of very small children (such as Pringles cans) can also prevent removal.
o Enlist the doctor’s help during your visits. If you are losing this battle, make sure the doctor is aware.