Amblyopia is poor vision in an eye that did not develop normal sight during early childhood. It is sometimes called “lazy eye.” When one eye develops good vision while the other does not, the eye with poorer vision is called amblyopic. Usually, only one eye is affected by amblyopia, but it is possible for both eyes to be “lazy.”

Amblyopia is common, affecting approximately 2-3 out of every 100 people. The best time to correct amblyopia is during infancy or early childhood. People with amblyopia in one eye are more than twice as likely to lose vision in the healthy eye from trauma.

Newborn infants are able to see, but as they use their eyes during the first months of life, vision improves. During early childhood years, the visual system changes quickly and vision continues to develop. If a child cannot use his or her eyes normally, vision does not develop properly and may even decrease. After the first nine years of life, the visual system is usually fully developed and usually cannot be changed. The development of equal vision in both eyes is necessary for normal vision.

A newborn cannot properly focus on an object at birth. Babies must learn to focus both eyes in the same way that they learn to control their motor skills. If a child is incapable of focusing both eyes, they will experience double vision. This is frustrating; consequently, they will learn to rely on only one eye for vision. Prolonged use of only one eye deteriorates the nerves to the unused eye, resulting in a condition called amblyopia, which is often called lazy eye. Amblyopia has three major causes.

• Strabismus (Misaligned Eyes): Amblyopia occurs most commonly with misaligned or crossed eyes. The crossed eye “turns off” to avoid double vision and the child uses only the better eye. The misaligned eye then fails to develop good vision.

• Unequal Focus (Refractive Error): Amblyopia occurs when one eye is more near-sighted, far-sighted, or astigmatic compared to the other. This condition is called anisometropia. The unfocused (blurred) eye “turns off” and becomes amblyopic. The eyes can look normal but one eye has poor vision. This is most difficult type of amblyopia to detect since the child appears to have normal vision when both eyes are open.

• Cloudiness in Lens / Droopy Eyelid: An eye disease such as cataract (a clouding of the naturally clear lens of the eye) may lead to amblyopia. Any factor that prevents a clear image from being focused inside the eye can lead to the development of amblyopia in a child. A droopy eyelid covering the pupil in a child may lead to amblyopia.

It is not easy to recognize amblyopia. A child may not be aware of having one strong eye and one weak eye. Unless the child has a misaligned eye or other obvious abnormality, there is no way for parents to tell that something is wrong. Amblyopia is detected by finding a difference in vision between the two eyes. Since it is difficult to measure vision in young children, your ophthalmologist often estimates visual acuity by watching how well a baby follows objects with one eye when the other eye is covered.

Using a variety of tests, the ophthalmologist observes the reactions of the baby when one eye is covered. If one eye is amblyopic and the good eye is covered, the baby may attempt to look around the patch, try to pull it off or cry.

Poor vision in one eye does not always mean that a child has amblyopia. Vision can often be improved by prescribing glasses for a child. Your ophthalmologist will also examine the interior of the eye to see if other eye diseases may be causing decreased vision. These diseases include cataracts, inflammations, tumors, and other disorders of the inner eye.