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Amblyopia

Amblyopia, or lazy eye, is a disorder of the eye. It is characterised by poor or blurry vision in an eye that is otherwise physically healthy and normal. The problem is caused by either no transmission or poor transmission of the visual image to the brain for a sustained period of dysfunction or disuse during early childhood. The condition will only arise at this young age because most of the visual system's development in humans is complete and "locked in" by a few years of age. more...

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Amblyopia normally only affects one eye, but it is possible to be amblyopic in both eyes if both are similarly deprived of a good, clear visual image.

Amblyopia affects 2-5% of the population. Amblyopia is a developmental problem in the brain, not an organic problem in the eye. The part of the brain corresponding to the visual system from the affected eye is not stimulated properly and develops abnormally. This has been confirmed in brain specimens.

Many children who have amblyopia, especially those who are only mildly amblyopic, are not even aware they have the condition until tested at older ages, since the vision in their stronger eye is normal. However, people who have severe amblyopia may experience associated vision disorder, most notably poor depth perception.

Types

Amblyopia can be caused by deprivation of vision early in life, or by strabismus (misaligned eyes), vision obstructing disorders and anisometropia (different degrees of myopia or hyperopia in each eye).

Strabismic amblyopia

Strabismus, sometimes known as lazy eye, will result in normal vision in the fixating eye, but abnormal vision in the strabismic eye due to the brain discarding certain information. Strabismus usually develops into double vision (diplopia) in adulthood, since the two eyes are not fixated on the same object. Children's brains, however, are more plastic, and therefore can more easily adapt by ignoring images from one of the eyes, getting rid of the double vision. This plastic response of the brain, however, interrupts the brain's normal development, resulting in the amblyopia.

Strabismic amblyopia is best treated by treating the strabismus through the use of prescription glasses, vision therapy, surgery or patching.

Refractive amblyopia

If anisometropia is present, refractive amblyopia may result. Anisometropia exists when there is a difference in the refraction between the two eyes. The eye with less refractive error provides the brain with a clearer image, and is favoured by the brain. Those with this condition are more susceptible to the development of amblyopia, which may be as severe as strabismic amblyopia. Despite its severity, refractive amblyopia is commonly missed by primary care physicians because of its less dramatic appearance and lack of obvious physical manifestation, such as with strabismus .

Refractive amblyopia is diagnosed when there is a wide disparity in visual acuity between the two eyes. Refractive amblyopia is treated by correcting the refractive error early with prescription lenses. Vision therapy and/or eye patching can also be used to develop and/or improve visual abilities, binocular vision, depth perception, etc.

Read more at Wikipedia.org


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Waking up that lazy eye
From Science News, 5/14/05 by Nathan Seppa

In amblyopia--"lazy eye"--the brain prefers images from one eye over the other. Most doctors treat the condition in children by patching the good eye for part of each day, but assume that the practice doesn't work past age 10. Some doctors give up on patching at age 7.

A U.S.-Canadian study now finds that children up to age 17 can make significant gains in vision by wearing a patch.

Researchers identified 507 children with amblyopia and randomly assigned half of them to wear a patch from 2 to 6 hours a day for 24 weeks. If needed, the kids also received prescriptions for eyeglasses. All the children were between 7 and 17 years old.

Children ages 7 to 12 who wore patches were four times as likely as those who didn't to improve their vision in the weak eye by two rows on the standard 11-line eye chart that doctors use to assess eyesight, the scientists report in the April Archives of Ophthalmology. Kids with amblyopia usually have a lazy eye that reads down to only the middle of the chart. People with normal vision see down to about the 10th row.

Children 13 to 17 also gained some visual clarity by wearing a patch, but only if they hadn't received such therapy earlier in their lives. Their gains were smaller than those of 7-to-12-year-olds but still significant, says study coauthor Richard W. Hertle of the University of Pittsburgh.

Long-term follow-up might reveal whether the vision improvements are permanent, Hertle says.

COPYRIGHT 2005 Science Service, Inc.
COPYRIGHT 2005 Gale Group

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