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.
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. The three major causes of amblyopia are:
- 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 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 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 since the child appears to have normal vision when both eyes are open.
- Cloudiness in the clear tissues of the eyes:
An eye disease such as a cataract 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.
It is not easy to recognize amblyopia, since a child may not be aware of having one strong eye and one weak eye. Amblyopia is detected by finding a difference in vision between the two eyes. Since it is difficult to to measure vision in young children, the eye doctor often estimates visual acuity by watching how well a baby follows objects with one eye when the other eye is covered.
To correct amblyopia, a child must be made to use the weak eye. This is usually done by patching or covering the strong eye, often for weeks or months.
Even after vision as been restored in the weak eye, part-time patching may be requered over a period of years to maintain the improvement.
Glasses may be prescribed to correct errors in focusing. If glasses alone do not improve vision, then patching is necessary. Occasionally, amblyopia is treated by blurring the vision in the good eye with special eye drops or lenses to force the child to use the amblyopic eye.
Amblyopia cannot usually be cured by treating the cause alone. The weaker eye must be made stronger in order to see normally. If amblyopia is not treated, several problems may occur:
- the amblyopic eye may develop a serious and permanent visual defect;
- depth perception (seeing in three dimensions) may be lost;
- if the good eye becomes diseased or injured, a lifetime of poor vision may be the result.
Success in the treatment of amblyopia depends upon its severity and how old the child is when treatment begins. If the problem is detected and treated early, vision can improve for most children. Sometimes part-time treatment may have to continue until the child is about nine years old. After this time, amblyopia usually does not recur.
If amblyopia is first discovered after early childhood, treatment may not be successful. Amblyopia caused by strabismus or unequal refractive errors may be treated succcessfully at a much older age than the amblyopia caused by cloudiness in tissues in the eye.