Lazy eye (amblyopia)

Lazy eye (amblyopia) is reduced vision in one eye caused by abnormal visual development early in life. The weaker — or lazy — eye often wanders inward or outward.

Amblyopia generally develops from birth up to age 7 years. It is the leading cause of decreased vision among children. Rarely, lazy eye affects both eyes.

Early diagnosis and treatment can help prevent long-term problems with your child's vision. The eye with poorer vision can usually be corrected with glasses or contact lenses, or patching therapy.

Signs and symptoms of lazy eye include:

• An eye that wanders inward or outward
• Eyes that appear to not work together
• Poor depth perception
• Squinting or shutting an eye
• Head tilting
• Abnormal results of vision screening tests

Sometimes lazy eye is not evident without an eye exam.

See your child's doctor if you notice his or her eye wandering after the first few weeks of life. A vision check is especially important if there's a family history of crossed eyes, childhood cataracts or other eye conditions.

For all children, a complete eye exam is recommended between ages 3 and 5.

Lazy eye develops because of abnormal visual experience early in life that changes the nerve pathways between a thin layer of tissue (retina) at the back of the eye and the brain. The weaker eye receives fewer visual signals. Eventually, the eyes' ability to work together decreases, and the brain suppresses or ignores input from the weaker eye.

Anything that blurs a child's vision or causes the eyes to cross or turn out can result in lazy eye. Common causes of the condition include:

• Muscle imbalance (strabismus amblyopia). The most common cause of lazy eye is an imbalance in the muscles that position the eyes. This imbalance can cause the eyes to cross in or turn out, and prevents them from working together.

• Difference in sharpness of vision between the eyes (refractive amblyopia). A significant difference between the prescriptions in each eye — often due to farsightedness but sometimes to nearsightedness or an uneven surface curve of the eye (astigmatism) — can result in lazy eye.

  Glasses or contact lenses are typically used to correct these refractive problems. In some children lazy eye is caused by a combination of strabismus and refractive problems.

• Deprivation. A problem with one eye — such as a cloudy area in the lens (cataract) — can prohibit clear vision in that eye. Deprivation amblyopia in infancy requires urgent treatment to prevent permanent vision loss. It's often the most severe type of amblyopia.

Factors associated with an increased risk of lazy eye include:

• Premature birth
• Small size at birth
• Family history of lazy eye
• Developmental disabilities

Untreated, lazy eye can cause permanent vision loss.