Lazy eye, medically known as amblyopia (am-blee-OH-pee-a), is the loss or lack of development of vision, usually in one eye. It affects about 2 percent of children and is rare among adults. In most cases, the abilities of one eye are limited so it does not develop properly. The brain gives preference to the dominant eye. If left untreated, the brain will eventually “ignore” images from the weaker eye, and eventually its nerve connections degenerate.
This degenerative process usually begins with an inherited condition and appears during infancy or early childhood. Lazy eye needs to be diagnosed between birth and early school age (age 8 or 9), since it is during this period that brain “chooses” its visual pathway and may ignore the weaker eye permanently. Even with early treatment, ongoing complications and recurrence are possible.
There are several underlying causes, including:
Crossed eyes (strabismus). This causes double vision (diplopia) when children use both eyes at the same time. One image may appear clearer than the other, and the brain will block out the weaker image when double vision is prolonged.
- Focus inequality, in which one eye is much more nearsighted, farsighted or astigmatic than the other. Again, the brain gives preference to the stronger eye.
- Structural problems in the eye or eyelid, such as a
cataract or ptosis (a drooping eyelid).
Lazy eye is not always easy to recognize, since a child with worse vision in one eye does not necessarily have lazy eye. This is why all children – including those with no symptoms – should get a complete eye examination by age 3, and sooner if there is a family history of any eye condition or disease or if you detect any of these symptoms:
- The ability to see well on only one side, or clearly seeing some but not all objects clearly
- Trouble judging depth or distance
- Covering one eye to see, or tilting the head to read or perform other activities
- Frequent rubbing or winking
- Bumping into objects on the side of the weaker eye or other signs of clumsiness
- Infants may cry if one eye is covered
To prevent permanent loss of vision in a "weak" eye, newborns should receive an eye exam to rule out congenital abnormalities. Visual acuity testing should begin by age 3, and be done at least annually thereafter. If the results of a screening exam suggest that your child has lazy eye, you will be referred to an ophthalmologist for further testing and assessment.
Treatment is usually successful with prompt intervention and treatment. There are three goals: correcting the underlying problems, strengthening the weaker eye and producing a clear visual image in both eyes. To achieve this, your eyecare practitioner may employ:
Eyeglasses with prism, concave, convex or bifocal lenses to strengthen and restore focus to the weaker eye, encouraging the brain to use it over time. Eyeglasses can also be used to treat focus inequality caused by conditions such as nearsightedness or farsightedness.
Contact lenses are also used in cases of severe refractive inequality (between the two eyes), or a single contact lens may be prescribed for the amblyopic eye.
Monitored patching consists of covering the stronger eye for defined periods – usually for at least 6 months – to strengthen the muscles that control the weaker eye. Once the child’s vision is restored, occasional patching may still be needed for several years. As an alternative, some doctors use an opaque contact lens or prescribe atropine eye drops to temporarily blur vision in the stronger eye.
Vision therapy, or orthoptics, can strengthen, coordinate and improve the functions of both eyes, especially in the early years of life.
Surgery can “reposition” eye muscles to restore permanent control of the weaker eye. If cataracts are the cause of the amblyopia, they must be surgically removed. After cataract removal, an artificial lens can restore focus, and eventually restore strength to the weaker eye. Other surgical procedures may also be beneficial when other eye diseases are the cause.