Amblyopia | Overview
What is amblyopia?
The visual system develops rapidly during a child’s first seven to ten years, when important connections that allow light to pass back and forth between the brain and the optic nerves develop. Amblyopia, also known as “lazy eye,” occurs when the brain favors one eye and develops pathways to only one eye. The condition typically begins in infancy or early childhood.
Amblyopia is the most common cause of vision problems in children, affecting 2 to 3 out of every 100 kids. If treated early, it can often be corrected. Left untreated, amblyopia can permanently impair vision and depth perception.
The condition often runs in families. A child’s chances of developing amblyopia are greater if a parent or a sibling has the condition.
There are three kinds of amblyopia:
- Refractive amblyopia – This form of amblyopia may occur when there is a focusing difference between the two eyes. This may be caused by conditions such as astigmatism, hyperopia, or myopia. The brain only sees with the stronger eye, and as a consequence, the vision in the weaker eye does not develop. In some cases, vision may not develop in either eye properly when there is a significant focusing problem of both eyes. Because there are no visible signs of this type of amblyopia, and the child may not realize there is a problem, the condition often goes undetected until a child’s vision test.
- Strabismic amblyopia – This form of amblyopia may occur when the eyes are not aligned properly and one eye crosses outward or inward. Strabismus and amblyopia affect between 2 and 4 percent of the population.
- Deprivation amblyopia – This form of amblyopia may develop when a child has cataracts in one or both eyes that impair their vision. Cataracts are rare in children but can run in families. Cataracts be present at birth, shortly after birth, or develop as a result of trauma, steroid use, or other childhood diseases.
Doctors recommend treating a child with amblyopia before the age of 7, while the brain is still maturing, but for the best possible results, treatment should start before age 5. While treatment can improve vision for teenagers with amblyopia, there is no treatment that can restore vision to normal at that age.
What are the symptoms of amblyopia?
Symptoms of amblyopia are usually subtle, if they exist at all. The child may not notice that anything is wrong and may not say anything. Parents or teachers may notice one of the following symptoms:
- misaligned eyes (strabismus)
- frequent squinting, or difficulty seeing
- tilting or turning their head to see better
- closing or covering an eye to see
Since the eye without amblyopia has excellent vision, there are usually no symptoms, and amblyopia is most often discovered during a routine vision exam.
What causes amblyopia?
Amblyopia occurs when one eye sees better than the other eye and the brain ignores the blurred images from the other eye. Connections between the brain and the stronger eye get stronger and the connections between the brain and the weaker eye decline.
The following visual problems can trigger amblyopia:
- Refractive errors: Astigmatism, hyperopia or myopia – the shape of the eye does not bend light correctly so the child’s vision is blurred in one eye, nearsighted or farsighted. Refractive errors can be corrected with eyeglasses but in young children refractive errors have few symptoms and are only detected with a vision test.
- Strabismus: A child’s eye can cross for no apparent reason. The eye and brain become misaligned so the eyes point in different directions. The brain compensates by ignoring the signals from the crossed eye. The eye that is ignored loses vision from amblyopia.
- Structural issue: A droopy eyelid or cataract in one eye impairs vision and the brain responds by paying attention to healthy eye and ignoring the poor image in the eye with impairment.
Amblyopia tends to run in families. A child is at greater risk for developing the condition if a parent or sibling had amblyopia. Children born prematurely or who have developmental delays are also at greater risk.
How we care for amblyopia
The Department of Ophthalmology at Boston Children's Hospital offers the latest and best in diagnostics and care for children with amblyopia and other vision problems. Children and families come from around the world to our Eye Center for the most advanced vision testing, diagnostics and treatment available for of all types of visual impairments.
Amblyopia | Diagnosis & Treatment
How is amblyopia diagnosed?
All children should have a vision test before their fourth birthday. Most pediatricians test vision as part of the standard medical exam and refer the family to an ophthalmologist if they detect signs of a problem.
While checking a child’s vision, the pediatrician or ophthalmologist may cover one eye at a time and see how well the child can follow an object with the other eye. They may also watch the child’s reaction to having an eye covered. If the child becomes upset or tries to pull the cover away, it could be a sign of amblyopia.
How is amblyopia treated?
The sooner amblyopia is caught and treated, the better the child’s chances for a positive outcome.
Treatment depends on what type of amblyopia a child has, and how severe it is.
Children with refractive amblyopia, lazy eye caused by astigmatism, nearsightedness or farsightedness, are typically treated with patching. This non-invasive procedure involves blocking the stronger eye, thus forcing the brain to see out of the weaker eye. The ophthalmologist may suggest one or more of the following forms of patching:
- a patch over the stronger eye
- eye drops to temporarily blur the vision in the stronger
- eye eyeglasses that blur the vision in the stronger eye
Patching can take weeks or months to take effect and may need to be continued part time for several years to ensure equally strong vision in both eyes.
Mild cases of strabismus can often be treated effectively with prescription glasses or patching. If a child has severe strabismus, the ophthalmologist may recommend surgery to realign the crossed eye with the brain.
Surgery involves detaching the muscle or muscles that are pulling the eye out of alignment and reattaching it or them to a new spot.
A few hospitals offer Botox injection, a minimally invasive procedure that temporarily weakens the muscle that is pulling the eye out of alignment.
If amblyopia is caused by cataracts, the treatment will depend on the age of the child and size of the cataract. As a general rule, the older the child, the less urgent it is to perform cataract surgery right away. If the cataract is a tiny dot on the lens, the doctor may recommend patching and possibly having the child wear glasses or contact lenses. Patching the unaffected eye forces the eye with the cataract to develop better vision.
Children born with dense cataracts need surgery as soon as possible. During surgery, the cloudy lens is removed and may be replaced with an intraocular implant, a clear, plastic permanent lens. However, due to the risk of complications, an intraocular implant may not be the best option for a very young child. In such cases, the child may instead be fitted with a specialty contact lens a few days after the surgery. This may be a temporary solution to help the child see until they are old enough for implant surgery or the eye may work fine with the contact lens and not require further surgery.