A lazy eye, also called amblyopia, means that one eye has not connected properly to the brain; it's blurry even with the best glasses or contacts the eye doctor can prescribe.
|Clear vision out of an eye with normal sight||
Blurry vision out of a lazy eye, even with glasses
Amblyopia is caused when the brain favors one eye and refuses to use the other. Simply stated, amblyopia is a dysfunction of the brain which blocks vision from one eye because it can't use the two eyes together. Because the eye is "turned off, " clear vision does not develop in the lazy eye. Amblyopia affects 2 to 3 percent of the population.
How a Lazy Eye Develops
Children with normal vision learned to use both eyes together in the first few months of life. Their brains developed the ability to take the pictures coming in from both their left and right eyes and "fuse" the two pictures into a single image. This is called "binocularity," or normal two-eyed vision.
The brains of children who have a lazy eye, however, did not learn to use their two eyes together. At an early age, these children only used one eye, and their brain "turned off" or blocked the in-coming picture from the other eye. Turning off an eye is called suppression. Because the brain suppressed the lazy eye very early in life, normal sharpness of vision, called acuity, did not have a chance to develop. This "use it or lose it" syndrome means that the child has lost the ability to see clearly out of the lazy eye, even with the best pair of glasses or contacts the eye doctor can prescribe. How poor the vision is in the weak eye depends in part upon how early in the child’s visual development the brain turned the eye off.
Refractive Amblyopia: One type of lazy eye, called refractive amblyopia, is caused when one eye is has a different prescription strength, making it difficult for the eyes to focus together.
Strabismic Amblyopia: Another common cause of lazy eye is strabismus. Strabismus, often referred to as a crossed or wandering eye, is a condition in which the brain is unable to properly align the eyes. As a result, one eye may point in or out, up or down. When the eyes are not pointing at the same place, two different pictures are being sent to the brain. Because the brain can't combine two obviously different pictures into a single image, the result is double vision. The brain is then forced to turn off the picture coming in from the misaligned eye to avoid seeing double. The child only uses his straight eye to see, and vision in the turned eye does not have a chance to develop. (See our web page on "Crossed Eyes" for more complete information on strabismus.)
Misconceptions about the "Critical Stage" for Treatment
Some parents are told that a lazy eye can only be corrected when the child is very young, usually age six (or 9) or under, the time when a child's visual system is still naturally "moldable." Some doctors feel that if treatment is not undertaken during this "critical stage" of development, the amblyopia becomes fixed and untreatable. Parents of older children with lazy eyes are often told that it is too late to treat the problem.
New research has disproven this completely. Lazy eyes can be treated at any age.
Vision therapy is highly successful in correcting a lazy eye. At least 95% of patients treated fully in office based vision therapy will have full resolution of their amblyopia!
During therapy, the patient's brain is trained to stop suppressing the lazy eye, the visual pathways from brain to eyes are improved so the patient can keep both eyes aligned, and finally the brain is taught to fuse the images coming in from both eyes for normal binocular ("two-eyed") vision. And this can be done at any age.
A lazy eye is not always easily recognized. A child may not even be aware that one of his eyes is not working with the other. If the eye turn is so slight that the child does not have an obvious misalignment, parents will rarely be able to tell something is wrong just by looking.