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Thursday, August 10, 2006

Amblyopia: What is it?


What Is Amblyopia?

Amblyopia, also known as "lazy eye," is reduced vision - uncorrectable with lenses - in an eye that has not received adequate use during early childhood. There is no visible anatomical defect.

Amblyopia has many causes. Most often it results from either a misalignment of a child's eyes, such as crossed eyes (strabismus), or a difference in image quality between the two eyes (one eye focusing better than the other, also known as anisometropia). In both cases, one eye becomes stronger, suppressing the image of the other eye. If this condition is not treated in early childhood, the weaker eye may become permanently impaired. With early diagnosis, amplyopia can be treated and loss of vision prevented.

What Are the Different Types of Amblyopia?

Strabismic amblyopia and anisometropic amblyopia are the two most common types. In strabismic amblyopia, the child has strabismus and the eyes are not aligned correctly so that one eye sees a different image from the other. In the eye that is deviated, the images seen by visual brain cells are suppressed to avoid double vision.

With anisometropic amblyopia, the eyes possess differing refractive powers. For example, one eye may be near-sighted while the other is far-sighted or strongly astigmatic. As a result, the brain will favor the eye with the clearer image and begin to ignore signals from the other one.

What Causes Amblyopia to Develop?

Amblyopia develops when any of the following conditions occur in an infant or young child:

  • "Squint"/strabismus (eyes not positioned straight)
  • Congenital cataract (clouding of the lens in an infant)
  • Uncorrected high near-sightedness (myopia) or far-sightedness (hyperopia) in both eyes
    other)
  • Uncorrected high myopia or hyperopia in one eye (one eye focuses differently from the
  • Severe ptosis (droopy eyelids)


Why Does Amblyopia Develop?

Amblyopia develops because when one eye is turned, as in squint, two different pictures are sent to the brain. In a young child, the brain learns to ignore the image of the deviated eye and see only the image of the better eye.

Similarly when there is difference in refractive power between the two eyes, the blurred image formed by the eye with greater uncorrected power is avoided by the brain. A moderate or high degree of refractive power present in both eyes, when not corrected early and adequately, results in amblyopia.

In order that the retina may register an object, it needs adequate light and visual stimulus. When these factors are absent, as in the presence of cataract in an infant, amblyopia also results.

Symptoms



  • Eye turning in, out or up
  • Closing one eye (particularly in bright sunlight)
  • Squint
  • Headaches or eyestrain


Risk Factors

Children under nine years of age whose vision is still developing are at highest risk for amblyopia. Generally, the younger the child, the greater the success of treatment. An older child may not achieve normal vision with treatment.

What You Can Do to Reduce Risk

Since amblyopia is caused by many conditions, such as strabismus, near-sightedness (myopia) or far-sightedness (hyperopia), the diagnosis and successful treatment of these vision conditions should reduce the risk of amblyopia.

Treatment

Amblyopia can often be reversed, or at least reduced, if it is detected and treated early. Cooperation of the patient and parents is required to achieve good results. If left untreated or if not treated properly, the reduced vision of amblyopia becomes permanent and vision cannot be improved by any means.

The most effective way of treating amblyopia is to encourage the child to use the amblyopic eye. Covering or patching the good eye to force use of the amblyopic eye may be necessary to ensure equal and normal vision. This can be achieved by:

  • prescribing proper spectacles if the patient is found to have refractive error or accommodative esotropia;
  • prescription of drops such as Phospholine Iodide to reduce the accommodative effort that causes accommodative esotropia;
  • removal of cataract when indicated;
  • occluding the normal eye, for example, with a patch;
  • surgery, when amblyopia is accompanied by strabismus and is unresponsive to conservative treatment.

When occlusion is decided upon, the treatment may vary from a few hours to months or even years depending upon the age of patient, the type and severity of amblyopia, and the response. In cases experiencing less severe amblyopia, partial occlusion, such as that by making one glass frosted, may be sufficient. Older children can do reading exercises at home while patching the normal eye. Those patients who are patching their eyes need periodic follow-up, which is scheduled with an optometrist or ophthalmologist.

Facts on Patching



  • Patching is not a pleasant thing for a child, so initially the child will be reluctant to undergo it. It is our duty to encourage the child to understand the importance of cooperation.

  • In a young child, patching is done for shorter periods initially; the duration is increased gradually to obtain better compliance.

  • Acceptance is good as soon as vision is increased in the ambloypic eye.

  • Method of patching should be according to the circumstances of the child:

    • Patch should be placed directly on the face over the eye.
    • If the child wears glasses, the patch should be placed over the eye, not on the glasses.
    • Glasses can also be used as an occluder in older children.
    • Many children try to take the patch off. This problem usually disappears as the child grows accustomed to wearing the patch.
    • Precautions must be taken to prevent the child from peeking around the edge of the patch.
    • Patching schedules should be followed strictly.
    • Patching should not be stopped abruptly. The program should be tapered only by ophthalmologists or optometrists.
    • Regular follow-up visits are a must.


Article Source:
Aravind Eye Hospitals and Postgraduate Institute of Ophthalmology: http://www.aravind.org/patient/amblyopia.htm

© 2003 Aravind Eye Hospitals and Postgraduate Institute of Ophthalmology

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