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Amblyopia

What is Amblyopia?

Illustration of amblyopia or lazy eye

A common vision problem in children is amblyopia, or ”lazy eye.” It is so common that it is the reason for more vision loss in children than all other causes put together. Amblyopia is a decrease in the child’s vision that can happen even when there is no problem with the structure of the eye.

The decrease in vision results when one or both eyes send a blurry image to the brain. The brain then “learns” to only see blurry with that eye, even when glasses are used. Only children can get amblyopia. If it is not treated, it can cause permanent loss of vision.

Types of Amblyopia

There are several different types and causes of amblyopia: Strabismic amblyopia, deprivation amblyopia, and refractive amblyopia. The end result of all forms of amblyopia is reduced vision in the affected eye(s).

Strabismic Amblyopia

Strabismic amblyopia develops when the eyes are not straight. One eye may turn in, out, up, or down. When this happens, the brain “turns off” the eye that is not straight and the vision subsequently drops in that eye.

Deprivation Amblyopia

Deprivation amblyopia develops when cataracts or similar conditions “deprive” young children’s eyes of visual experience. If not treated very early, these children can have very poor vision. Sometimes this kind of amblyopia can affect both eyes.

Refractive Amblyopia

Refractive amblyopia happens when there is a large or unequal amount of refractive error (glasses strength) in a child’s eyes. Usually, the brain will”turn off” the eye that has more farsightedness or more astigmatism. Parents and pediatricians may not think there is a problem because the child’s eyes may stay straight.

Also, the “good” eye has normal vision. For these reasons, this kind of amblyopia in children may not be found until the child has a vision test. This kind of amblyopia can affect one or both eyes and can be helped if the problem is found early.

Causes & Symptoms

Amblyopia occurs when the brain and eyes do not work together properly. In persons with amblyopia, the brain favors one eye.

The preferred eye has normal vision, but because the brain ignores the other eye, a person’s vision ability does not develop normally. Between ages 5 and 10, the brain stops growing and the condition becomes permanent.

Strabismus is the most common cause of amblyopia, and there is often a family history of this condition.

Other causes include:

Symptoms include:

Treatment & Prognosis

Amblyopia is usually easily diagnosed with a complete examination of the eyes. Special tests are usually not required.

Treatment

One of the most important treatments of amblyopia is correcting the refractive error with consistent use of glasses and/or contact lenses.

Other mainstays of amblyopia treatment are to enable as clear an image as possible (for example, by removing a cataract), and forcing the child to use the nondominant eye (via patching or eye drops to blur the better-seeing eye). Sometimes, drops are used to blur the vision of the normal eye instead of putting a patch on it.

The underlying condition will also require treatment. For the treatment of crossed eyes, see: Strabismus

Children whose vision cannot be expected to fully recover should wear glasses with protective lenses of polycarbonate, as should all children with only one good eye caused by any disorder. Polycarbonate glasses shatter and scratch-resistant.

Prognosis

Children who receive treatment before age 5 usually have a near-complete recovery of normal vision. Delaying treatment can result in permanent vision problems. After age 10, only a partial recovery of vision can be expected.

Possible complications include eye muscle problems that may require several surgeries and permanent vision loss in the affected eye.

FAQ’s

Maybe, but they may not correct it all the way to 20/20. With amblyopia, the brain is “used to” seeing a blurry image and it cannot interpret the clear image that the glasses produce. With time, however, the brain may “relearn” how to see and the vision may increase.

Remember, glasses alone do not increase the vision all the way to 20/20, as the brain is used to seeing blurry with that eye. For that reason, the normal eye is treated (with patching or eye drops) to make the amblyopic (weak) eye stronger.

Bilateral amblyopia is usually treated with consistent, early glasses, and or contact lenses with follow-up over a long period of time. If asymmetric amblyopia (one eye better than the other) occurs, then patching or eye drops may be added.

Early treatment is always best. If necessary, children with refractive errors (nearsightedness, farsightedness, or astigmatism) can wear glasses or contact lenses when they are as young as one week old.

Children with cataracts or other “amblyogenic” conditions are usually treated promptly in order to minimize the development of amblyopia.

A recent National Institutes of Health (NIH) study confirmed that SOME improvement in vision can be attained with amblyopia therapy initiated in younger teenagers (through age 14 years). Better treatment success is achieved when treatment starts early, however.

Some forms of amblyopia, such as that associated with large-deviation strabismus, may be easily detected by parents. Other types of amblyopia (from high refractive error) might cause a child to move very close to objects or squint his or her eyes.

Still, other forms of amblyopia may NOT be obvious to parents and therefore must be detected by Vision Screening.

Vision Screening is strongly recommended by the American Academy of Pediatrics (AAP) over the course of childhood to detect amblyopia early enough to allow successful treatment.

Pediatricians check newborns for the red reflex to find congenital cataracts. Infants are checked for the ability to fix and follow and whether they have strabismus.

Toddlers can have their pupillary red reflexes tested with a direct ophthalmoscope (Brückner Test) or by photo screening, or by remote autorefraction to identify refractive errors that can cause amblyopia.

When children can consistently identify objects either by reading or by matching, the acuity of each eye (with the non-tested eye patched or covered) is screened to identify amblyopia.

Patching should only be done if an ophthalmologist recommends it. An ophthalmologist should regularly check how the patch is affecting the child’s vision.

Although it can be hard to do, patching usually works very well if started early enough and if the parents and child follow the patching instructions carefully. It is important to patch the dominant eye to allow the weak eye to get stronger.

The classic patch is an adhesive”Band-Aid” which is applied directly to the skin around the eye [See figure 3]. These may be available in different sizes for younger and older children.

For children wearing glasses, both cloth and semi-transparent stickers (Bangerter foils) may be placed over or onto the spectacles.”Pirate” patches on elastic bands are especially prone to”peeking” and are therefore only occasionally appropriate.

Sometimes the stronger (good) eye can be “penalized” or blurred to help the weaker eye get stronger. Blurring the vision in the good eye with drops or with extra power in the glasses will penalize the good eye [See figure 4]. This forces the child to use the weaker eye.

Ophthalmologists use this treatment instead of patching when the amblyopia is not very bad or when a child is unable to wear the patch as recommended.

For mild and moderate degrees of amblyopia, studies have shown that patching or eye drops may be similarly effective. Your pediatric ophthalmologist will help you select a treatment regimen that is best for your child.

Not all children benefit from eye drop treatment for amblyopia. Penalizing eye drops (such as atropine) work less well when the stronger eye is nearsighted.

The mainstay of treating amblyopia is patching of the dominant (good) eye, either full or part-time during waking hours.

Although classic teaching suggests that the more hours per day patching is performed, the greater the result, recent studies suggest that shorter periods may achieve similar results as longer amounts of patching in patients with moderate amounts of amblyopia.

Although vision improvement frequently occurs within weeks of beginning patching treatment, optimal results often take many months.

Once the vision has been improved, part-time (maintenance) patching or periodic use of atropine eye drops may be required to keep the vision from slipping or deteriorating. This maintenance treatment may be advisable for several months to years.

The particular activity is not terribly important, compared to the need to keep the patch on during the allotted time. As long as the child is conscious and has his or her eyes open, visual input will be processed by the amblyopic eye.

On the other hand, the child may be more cooperative or more open to bargaining if patching is performed during certain, desirable activities (such as watching a preferred television program or video).

Some eye doctors believe that the performance of near activities (reading, coloring, hand-held computer games) during treatment may be more stimulating to the brain and produce better or more rapid recovery of vision.

In many instances, school is an excellent time to patch, taking advantage of a nonparental authority figure. Patching in school hours gives the class an opportunity to learn valuable lessons about accepting differences between children.

While in most instances, children may not need to modify their school activities while patching, sometimes adjustments such as sitting in the front row of the classroom will be necessary.

If the patient, teacher, and classmates are educated appropriately, school patching need not be a socially stigmatizing experience.

On the other hand, frequently a parental or another family figure may be more vigilant in monitoring patching than is possible in the school setting. Parents should be flexible in choosing when to schedule patching.

Many children will resist wearing a patch at first. Successful patching may require persistence and plenty of encouragement from family members, neighbors, teachers, etc.

Children will often throw a temper-tantrum, but then they eventually learn not to remove the patch. Another way to help us is to provide a reward to the child for keeping the patch on for the prescribed time period.

Surgery on the eye muscles is a treatment for strabismus – it can straighten misaligned eyes. By itself, however, surgery does not usually or completely help the amblyopia. Surgery to make the eyes straight can only help enable the eyes to work together as a team.

Children with strabismic amblyopia still need close monitoring and treatment for the amblyopia, and this treatment is usually performed before strabismus surgery is considered.

Children who are born with cataracts may need surgery to take out cataracts. After surgery, the child will usually need vision correction with glasses or contact lenses and patching.

In all cases, the goal is the best possible vision in each eye. While not every child can be improved to 20/20, most can obtain a substantial improvement in vision. Although there are exceptions, patching does not usually work as well in children who are older than 9 years of age.

In some cases, treatment for amblyopia may not succeed in substantially improving vision. It is hard to decide to stop treatment, but sometimes it is best for both the child and the family.

Children who have amblyopia in one eye and good vision only in their other eye can wear safety glasses and sports goggles to protect the normal eye from injury. As long as the good eye stays healthy, these children function normally in most aspects of society

More information about past and ongoing clinical studies regarding amblyopia can be found at the National Eye Institute website.

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