Because many eye problems begin at a young age, it is important that children receive good eye care. Untreated eye problems can get worse and cause problems in school, at home and later in adult life.
What Is Amblyopia?
- Vision loss in one or both eyes
- Not helped by glasses alone
- Main cause of vision loss in children
- Affects 2-3 out of every 100 children
What Are The Causes Of Amblyopia?
1. Difference in Refractive Error Between the Eyes
There is a difference in the refractive state of the two eyes, such that one eye may be normal and not require a corrective lens, while the other eye is too nearsighted (myopic) or too farsighted (hyperopic). The condition is called Anisometropia, or difference in refractive error between the two eyes. As a consequence, the eye that needs a corrective lens will have a blurred image projected to the back of the eye (retina) and, in turn, the brain receives a blurred image from that eye. The eye (actually the brain) then becomes amblyopic. This condition is also called anisometropic amblyopia. Anisometropic amblyopia is very insidious; the child looks perfectly normal but one eye is really very amblyopic. Treatment is often delayed because the parents think that the child is fine and that there is no reason to see an eye doctor for a comprehensive eye exam.
2. Refractive Error
When an infant or young child has an uncorrected refractive error; this is, s/he needs glasses but no one knows s/he needs glasses, the blurred vision caused by the uncorrected refractive error can lead to amblyopia in one or both eyes. This is why it is so important that infants and young children see an eye doctor for a comprehensive eye exam. This type of amblyopia is sometimes referred to as refractive amblyopia.
3. Misaligned Eyes
There is a difference in the alignment of the eyes such that, for example, one eye points straight ahead and the other eye turns in toward the nose or turns out away from the nose. When the eyes point in different directions, the child is "strabismic". When one or sometimes both eyes appear to turn in the condition is called esotropia or commonly called "crossed eyes". When one eye turns out away from the nose the condition is called exotropia or commonly called "wall-eyed". When the eyes are not aligned, the brain will receive two very different images from the eyes and to correct this problem of double vision (diplopia) the brain will suppress or "turn-off" one of the images to achieve single vision. It is believed that this suppression or turning-off of one eye's input to the brain leads to reduced vision in the eye that is suppressed and thus leads to amblyopia in the affected eye.
The fourth type of amblyopia is often referred to as deprivational amblyopia. Whenever the two eyes receive very different information or images, there is a high probability of amblyopia. For example, if a child is born with a cataract or cloudy lens such that only one eye receives a clear image and the eye with the cataract receives a blurred image, then the eye with the cataract will become amblyopic. If the infant has a problem with the cornea in one eye, or one eye has excessive matting such that the child keeps the one eye closed for a period of time - all of these conditions can lead to amblyopia. Deprivation amblyopia often develops early in life.
Misconception of the Term “Lazy Eye”
The term “lazy eye” is often misused by the general population when describing an eye that drifts inward (toward the nose) or outward (toward the ear). The medical term for eye misalignment is strabismus. A person who suffers from a "lazy eye" has a condition known as amblyopia.
A child with amblyopia actually possesses a lazy brain, rather than a lazy eye, because the brain shuts off power to one eye and uses a single eye to see while the other remains unfocused.
Although the most common cause of amblyopia is strabismus, a child can suffer from amblyopia because of nearsightedness or farsightedness without showing any visible signs. Sometimes a difference in glasses prescription between the eyes can cause amblyopia. Other causes may be cataracts and droopy eyelids.
Finally, untreated amblyopia may result in permanent vision loss that cannot be corrected later by glasses or surgery.