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.