With amblyopia, vision is decreased when one or both eyes send a blurry image to the brain causing the brain to "learn" to see blurry with one eye and to “turn off” that eye in order to favor the other eye. Amblyopia is responsible for more vision loss in children than all other causes.
What are the causes of amblyopia?
Underlying causes for decreased vision in a child’s eye may include refractive errors such as astigmatism or farsightedness, strabismus (a misaligned eye) or a cataract (cloudiness of the lens).
From Nemours' KidsHealth
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Often times, amblyopia goes undetected for months or even years because parents chalk up poor grades or athletic ability to a child not being academically or athletically gifted. But sometimes the solution is as easy as visiting the eye doctor.
Treatment for amblyopia can correct the way the brain processes visual images and, ultimately, strengthen vision. The earlier treatment starts, the better. Waiting or not getting a proper diagnosis for a child could lead to irreversible vision loss down the line.
From birth until about 6 years of age, vital connections are formed between a child's eyes and brain. Anything that blocks or blurs vision in one or both eyes may then inhibit or block the development of these connections. This can cause the brain to not fully recognize the images seen by one or both eyes.
When this happens, the brain begins to ignore or suppress the images seen by the otherwise healthy eye, and the eye becomes weaker, losing vision strength (acuity). This eye is then referred to as "amblyopic."
The most common cause of amblyopia is strabismus, or wandering of one or both eyes either inward (called esotropia), outward (called exotropia), up (hypertropia), or down (hypotropia).
When eyes are misaligned, the straight or straighter eye becomes dominant. The vision strength (acuity) of the straight eye remains normal because the eye and its connection to the brain are functioning normally. The misaligned or weaker eye, however, does not focus properly and the brain suppresses or ignores its signal, eventually leading to amblyopia.
Not all kids with amblyopia will have crossed or wandering eyes — in fact many have eyes that are properly aligned. If so, amblyopia is usually the result of an anatomical or structural abnormality that interferes with or blocks vision, such as a droopy eyelid or a cataract.
Another cause of amblyopia is severe far-sightedness (hyperopia), near-sightedness (myopia), or astigmatism (a form of blurry vision). These vision problems ("refractive errors") cause vision to be blurry, and it's these blurry images that are sent to the brain. Over time, the brain begins to ignore or suppress these unclear images, resulting in amblyopia in one or both eyes.
Another cause could be having different vision strengths in each eye — a condition known as anisometropia. When one eye sees more clearly than the other, the brain can ignore or suppress the vision of the blurry eye.
Genetics play a role as well. Amblyopia tends to run in families. It's also more common in children born prematurely or those affected by developmental delays.
Signs & Symptoms
Most children with amblyopia won't complain of vision problems. Over time, they become accustomed to having good vision in one eye and poor vision in the other.
It's usually a parent or teacher who notices that a child is struggling with a vision problem — whether it's noticing crossed eyes, frequent squinting, or tilting the head to see better. Some kids will demonstrate poor depth perception (stereopsis) and difficulty seeing in 3D.
Treatment for amblyopia involves forcing the brain to pay attention to the images of the amblyopic or weaker eye so that vision in that eye gets stronger. This is done through glasses, eye patches or drops, surgery, or a combination of these treatments:
- Glasses. Glasses are prescribed when amblyopia is caused by severe refractive errors and/or anisometropia (when one eye sees more clearly than the other). Glasses help send clear, focused images to the brain, which will teach it to "switch on" the weaker eye. This allows the brain to use the eyes together and develop normal vision.
- Patches. In many cases, children affected by amblyopia must wear an opaque eye patch over their stronger or unaffected eye. The patch is worn for 2-6 hours a day while the child is awake for several months or years depending on the severity of the condition. There are two types of eye patches: the first type functions like a band-aid and is placed directly over the eye. The second type, designed specifically for kids who wear glasses, is a cloth patch that fits securely over one lens.
For parents, enforcing the use of an eye patch might seem challenging. But kids usually adapt well after an initial adjustment period, and the patch simply becomes part of their day. In the meantime, distraction with a new or exciting toy, a trip to the park, or just playing outside can help kids forget they're wearing an eye patch.
- Atropine drops. Sometimes despite parents' best efforts, some kids just refuse to wear their eye patch. In these cases, atropine drops may be used as an alternative to patches. Just as a patch blocks the vision in the unaffected or straight eye, atropine drops will temporarily blur out the vision in the strong eye, forcing the brain to recognize the images seen by the weaker eye.
- Surgery. If strabismus is the cause of a child's amblyopia and treatment with glasses, patches, or drops doesn't improve the alignment of the eyes, eye muscle surgery might be an option. Surgery also might be done if amblyopia is caused by a droopy eyelid or a cataract.
Surgery involves loosening or tightening the muscles that are causing the eye to wander. Although it is an invasive measure, surgery is considered safe and effective and usually does not require an overnight hospital stay.
Eye Exams Essential for Toddlers & Preschoolers
Kids reach visual maturity by about 8 years old; after that, vision problems can be harder to treat. The earlier amblyopia is diagnosed and treated, the better the chances to restore vision and avoid permanent vision loss.
Sometimes there are no apparent signs of a vision problem, so it's important for kids to undergo yearly vision screenings. These exams should begin in the toddler and preschool years so that problems are caught before a child reaches visual maturity.
Most vision screening exams are done at the pediatrician's office or at school by the school nurse. If problems are found, your child will be referred to a pediatric ophthalmologist for further evaluation and treatment.
If your child is due for a vision screening, call your doctor to schedule one.
Reviewed by: Jonathan H. Salvin, MD
Date reviewed: September 2011