How does normal vision develop?

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. Many occupations are not open to people who have good vision in one eye only.

If the vision in one eye should be lost later in life from an accident or illness, it is essential that the other eye have normal vision. Without normal vision in at least one eye, a person is visually impaired. For all of these reasons, amblyopia must be detected and treated as early as possible.

When should vision be tested?

It is recommended that all children have their vision checked by their pediatrician, family physician or ophthalmologist (medical eye doctor) at or before their fourth birthday. Most physicians test vision as part of a child’s medical examination. They may refer a child to an ophthalmologist if there is any sign of an eye condition. New techniques make it possible to test vision in infants and young children. If there is a family history of misaligned eyes, childhood cataracts or a serious eye disease, an ophthalmologist can check vision even earlier than age three.

What causes Amblyopia?

Amblyopia is caused by any condition that affects normal use of the eyes and visual development. In many cases, the conditions associated with amblyopia may be inherited. Children in a family with a history of amblyopia or misaligned eyes should be checked by an ophthalmologist early in life. 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.
• Unequal focus (refractive error). Refractive errors are eye conditions that are corrected by wearing glasses. Amblyopia occurs when one eye is out of focus because it is more nearsighted, farsighted or astigmatic than the other. The unfocused (blurred) eye “Turns off” and becomes amblyopic. The eyes can look normal but one eye has poor vision. This is the most difficult type of amblyopia to detect and requires careful measurement of vision.
• Cloudiness in the normally clear eye tissues. An eye disease such as a cataract (a clouding of the eye’s natural lens) 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. This is often the most severe form of amblyopia.

How is amblyopia diagnosed?

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, there is often 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 viewing how well a baby follows objects with one eye when the other 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 carefully examine the interior of the eye to see if other eye diseases may be causing decreased vision. These diseases include:

• Cataracts.
• Inflammations.
• Tumors.
• Other disorders of the inner eye.