Definition

Amblyopia, often called lazy eye, is a condition that occurs when there is a reduction of vision in one eye that is not correctable with glasses.

There are two common types of amblyopia:

• Anisometropic amblyopia—Vision in one eye differs from the other. This is often caused by a large difference in eyeglass prescription. The difference may be caused by one eye being more nearsighted or farsighted than the other, or by large differences in astigmatism.
• Strabismic amblyopia— Visible misalignment (crossing) of one eye.

The sooner amblyopia is treated, the more favorable the outcome.

Causes

Amblyopia is caused when the brain prefers (favors) one eye to the other. The brain’s preference (liking) for one eye over the other can weaken and reduce vision in the eye that is less used.

There are no apparent genetic or environmental factors that can be attributed to causing amblyopia.

Risk Factors

Amblyopia is more common in children under 10 years old with:

• Crossed eyes
• A large difference in sight between the two eyes that may be:
  • Unnoticed
  • Detected by a large difference in eyeglass prescription
• Visual blockage such as a cataract, droopy eyelid, or corneal scarring

Amblyopia can also occur in adults.

Symptoms

Some people with amblyopia may not have symptoms. In those that have them, amblyopia may cause:

• A droopy (the inability to fully-open) eyelid that blocks the pupil
• Headaches
• Blurry vision
• Excessive squinting or closing of the eyes
• Repeatedly closing of one eye in bright sunlight
• Crossing of one eye, generally the eye that is less used will excessively turn toward the nose

Symptoms vary depending on the extent of the amblyopia.

Diagnosis

Your eye doctor will ask about your symptoms and medical history. An examination of your eyes will be done. Since amblyopia tends to occur in young children, the types of tests their eye doctor will perform will be determined by their age and ability to respond.

Tests to evaluate the eyes may include:

• Visual acuity assessment testing (VAT)—to assess distant vision
• Cycloplegic refraction test—to assess how the eyeball displays and receives images produced by the lens of the eye
• Retinoscopy—to determine a preverbal child’s eyeglass prescription
• Prisms—to determine the amount of crossing between the 2 eyes

Treatment

Treatment includes correcting visual obstructions, such as cataracts and other visual abnormalities.

Talk to your doctor about the best option for you. These may include:

Prevention

While there are no current guidelines to prevent amblyopia, vision screening can help to detect the condition at an early age. Children under aged 3-5 (or younger) should be examined for eye problems.

National Eye Institute (NEI) http://www.nei.nih.gov/

The Canadian National Institute for the Blind http://www.cnib.ca

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