Encyclopedia - Amblyopia

What types of amblyopia exist?
How is amblyopia detected?
How is amblyopia corrected?

Amblyopia, or lazy eye, is poor vision in an eye that failed to develop normal sight during early childhood. It is usually caused by a lack of use of that eye because the brain has learned to favor the other eye. To protect a child's vision, amblyopia should be corrected during infancy or early childhood.

What types of amblyopia exist?

Any condition that affects normal use of the eyes and visual development can cause amblyopia. There are three major causes of amblyopia, and the condition is sometimes hereditary:

Strabismus is the most common cause of amblyopia and often occurs in eyes that are not aligned properly or are crossed. The crossed eye turns off to avoid double vision, and the other eye takes over most of the visual function. Because the brain favors one eye over the other, the nonpreferred eye is not adequately stimulated, and the brain cells responsible for vision in that eye do not mature normally.
Anisometropia refers to a condition where the eyes have unequal refractive power. For instance, one eye may be nearsighted and the other farsighted. Amblyopia occurs when the brain cannot balance this difference and chooses the easier eye to use. The eyes appear normal but, because the brain is using only one eye most of the time, the other has poor vision. This type of amblyopia is hard to detect and requires careful measurement of vision.
A third cause of amblyopia is any eye disease or injury that prevents a clear image from being focused inside the eye. For example, cataracts, which occur when the eye's natural lens becomes cloudy, can cause amblyopia.

How is amblyopia detected?

Unless an eye is misaligned, amblyopia is not easily detected, especially in a child. Children are often not aware that they have one strong eye and one weak eye because their sight has been that way since birth. And, without obvious abnormalities, there is no way for parents to tell that a problem exists with the child's vision. Therefore, you should schedule a comprehensive vision exam for your child to detect a difference in refractive power between the two eyes. Children should have their first exam by the age of 4. If you suspect any vision problems, if your child's eyes appear misaligned, or if there is a family history of amblyopia, you should schedule an appointment for your child at a younger age.

How is amblyopia corrected?

Treating the cause alone cannot cure amblyopia. Treatment always requires forcing the brain to use the nonpreferred eye. By patching the normal eye for most or part of the day, often for weeks or months, the brain must use the weaker eye. Even after vision has been restored in the amblyopic eye, part-time patching may be necessary to maintain improvement. To correct errors in focusing or to balance an unequal refractive power between both eyes, glasses may be prescribed. On occasion, special eye drops or lenses are used to blur vision in the good eye, forcing use of the amblyopic eye.

If a cataract causes amblyopia, the cloudy lens must be removed before the other eye can be patched. Following surgery, the patient may wear prescription eyeglasses or contact lenses to restore focusing, while patching improves vision.

Successful treatment of amblyopia depends on how severe the problem is and the age of the child when treatment begins. Treatment is sometimes less successful if the amblyopia is discovered after early childhood. If detected and treated early, however, vision can be improved for most children. Part-time treatment may have to continue until about age 9, after which time amblyopia usually does not return.

Correcting amblyopia can fail when the doctor's orders are not followed. Most children do not like eye patches, especially if they have been depending on the patched eye to see clearly. The parents must be interested and involved in the treatment, and the child must cooperate.