Amblyopia
Amblyopia is loss of vision that occurs because the brain ignores the image from the eye.
In amblyopia, vision loss is usually caused by the abnormal functioning of the brain, not of the eye. It develops only during childhood. Amblyopia is the most common cause of vision loss in children.
People have depth perception because the two images--one from each eye--are recorded from slightly different angles. The brain combines, or fuses, the separate images into one, three-dimensional picture. The brain develops the ability to fuse images only during childhood. When the input to the brain from one eye is of poor quality, such as a relatively blurred image or a double image, the brain suppresses the images, actually ignoring the input from that eye. The person is unaware of the image from one eye even though the eye itself is normal.
Causes
One of the most common causes of amblyopia is misalignment between the two eyes (strabismus). With strabismus, the eyes do not point to the same object, so the brain sees two very different images. These images are too different to be fused. In adults, seeing two different images results in double vision (diplopia). However, in children, if the ability to fuse images has not yet developed, the brain learns to ignore the image from the misaligned eye.
Similarly, poor vision in one eye (due to severe nearsightedness, farsightedness, or even congenital cataract) can impair a child's ability to fuse images. If the images the brain receives from the eyes are vastly different from each other, the brain learns to ignore the image that is more blurred.
Symptoms and Diagnosis
Children with amblyopia may be too young to describe symptoms. Or, a child may not realize that there is a problem, such as not being able to see out of one eye. Because only one image is perceived, the child lacks depth perception, although the child may not realize it.
In addition to performing a routine eye examination, doctors examine children at the earliest possible age for strabismus and refractive errors, which can cause amblyopia.
Prognosis and Treatment
Sometimes amblyopia is mild and temporary. Amblyopia is more likely to be permanent when it begins at an early age or persists for a long time. Amblyopia from any cause that has not been treated by the age of 10 usually cannot be fully reversed.
The sooner treatment is begun, the more likely amblyopia can be prevented or corrected. Treatment entails forcing the brain to use the visual images from the problem eye. Sometimes this is accomplished by correcting the vision in the problem eye with eyeglasses. The most effective way is to "handicap" the normal, stronger eye by putting a patch over it or giving eye drops that blur vision, such as atropine.
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