Amblyopia (pronounced am-blee-oh’-pee-ah) – also called lazy eye – is reduced visual acuity in one eye due to an interruption of the normal development of eyesight in that eye early in childhood. It can be mild (e.g. 20/40) to severe (20/200 or worse). Amblyopia is usually not correctable with lenses alone. But if it is detected early, patching the other eye and/or other vision therapy can improve vision in the amblyopic eye.
What causes amblyopia?
Newborn infants have relatively poor eyesight. But as they begin to use their eyes, vision gradually improves. For vision to develop properly, both eyes must be used equally and be capable of producing clear images. If the eyes aren’t properly aligned (a condition called strabismus), the brain will ignore images from one eye to prevent double vision. If this occurs regularly, the ignored eye will not develop 20/20 visual acuity. This is called strabismic amblyopia.
Amblyopia can also occur when the eyes are properly aligned, but one eye has significantly more nearsightedness, farsightedness or astigmatism than the other eye. The eye with the stronger refractive error is the one at risk to become amblyopic. This type of amblyopia is called refractive amblyopia.
Other potential causes of amblyopia include congenital cataracts or a drooping eyelid (called ptosis).
How common is amblyopia?
It is estimated that 2 to 4 percent of American children develop amblyopia.
What are the symptoms of amblyopia?
Unless there is a significant misalignment of the eyes, there are no obvious signs or symptoms of amblyopia. Because vision in the dominant eye is usually very good, a child with amblyopia rarely complains about their vision.
But these signs may occur:
A tendency to turn the head to the side (to favor the dominant eye).
A tendency to close one eye (especially in bright sunlight).
A tendency for one eye to drift when the child is tired.
General clumsiness or a tendency to bump into objects on one side.
Who is at risk?
Anyone can have amblyopia. It affects males and females equally. Factors that may increase a child’s risk of amblyopia include:
A family history of amblyopia
Low birth weight
How is amblyopia detected?
Amblyopia is detected by measuring the visual acuity of each eye separately to determine if a significant difference exists. But many young children with amblyopia manage to pass their school vision screenings (by peeking with their dominant eye when the amblyopic eye is being tested). Therefore, preschoolers should have a comprehensive eye exam by an optometrist or ophthalmologist to evaluate their visual acuity in both eyes and rule out the presence of amblyopia.
How is amblyopia treated?
To be effective, amblyopia must be treated in early childhood. If treatment hasn’t taken place by age 9 or 10, visual improvement in an amblyopic eye may be very limited. But if treatment begins before age 7, the likelihood of attaining 20/20 visual acuity in an amblyopic eye is quite good.
If amblyopia is due to strabismus (strabismic amblyopia), congenital cataracts, or droopy eyelids, surgery is performed to eliminate the underlying cause. After surgery, an ophthalmologist or optometrist will perform a refraction to determine if there is a need for corrective lenses. Patching of the dominant eye and other activities may be prescribed for a period of time (usually several weeks or months) to stimulate the development of vision in the amblyopic eye.
If amblyopia is due to unequal refractive error (refractive amblyopia), eyeglasses or contact lenses will be prescribed, along with patching and possibly other activities to stimulate vision in the amblyopic eye.
Patching must be monitored closely to make sure that it does not interfere with eye teaming or the normal visual development in the dominant (non-amblyopic) eye. The use of eye exercises and visual activities to treat amblyopia and other binocular vision disorders is called vision therapy (or vision training).