Reading an eye chart mounted or projected on a wall is a standard part of every visit to the optometrist today, but it wasn't always that way. Centuries ago, practitioners struggled to measure vis ...View Article
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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.
Amblyopia is caused by various conditions which prevent the brain from using both eyes together. In some cases, the tendency for a lazy eye may be inherited.
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. Refractive amblyopia starts early in life. An infant has no way of telling his parents one of his eyes isn't seeing as clearly as the other, so his visual system has to try to handle the problem on its own. The long-term suppression of the blurry eye causes vision to develop incorrectly. Once this type of lazy eye is discovered, prescribing glasses or contacts to help equalize the vision in both eye. Your specialist eye doctor can determine this prescription, even in an infant. It's not like the test you may have had where you answered question about the lenses the doctor shows you. ("which is better, 1 or 2")
Eye patching can help improve the sharpness of vision in the lazy eye. We use PEDIG study guides in our office to patch. The way you patch is CRITICAL to its success and MUST be done by a trained specialist.
Until, and unless, SUPPRESSION is treated fully to connect the brain and "lazy" eye, it will never be fully returned to normal. The great news is: the vast majority of amblyopia can be fixed, even at older ages, by proper treatment.
(Please see information below on how vision therapy can help a lazy eye.) Refractive amblyopia is the easiest type of lazy eye to correct.
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.)
To correct amblyopia, the proper glasses must be prescrbed first. When they are, many children will be cured just from this step. If not, patching the clear eye for specific periods of time, forcing the blurry eye to "turn on". Finally, if the underlying cause of the lazy eye is strabismus, then the eye turn must also be addressed.
Note: Recent research indicates that not nearly as much daily patching time is necessary as was previously thought. A study by the National Eye Institute showed that for many kids, 2 hours a day was as beneficial as patching six hours or more. Hopefully, most eye doctors are adapting their recommendations in light of the new research. If your eye doctor is recommending more than two hours of daily patching for your child, please referring him to this link for more information: www.childrensvision.com/eyecare-services/patching.html.
While patching usually improves vision, it is not always possible to restore the child to normal 20/20 vision with the patch alone, especially if the child had really poor eyesight in the eye to begin with. This is because strabismus, the underlying cause of the lazy eye, was never addressed. If you don't take care of the root of the problem, you still have it. For a permanent solution, the brain must be taught to stop suppressing the blurry eye and trained how to align and use the two eyes together--something a patch by itself cannot do. If this is not done, a child's visual system will still suppress the lazy eye once the patch is removed. As a result, some of the improvement from patching will be lost over time. Once patching is stopped, the vision in the lazy eye often degenerates if nothing has been done to teach the child's brain to use both eyes together.
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. The reason is called "neuroplasticity". It simply means our brains can learn new ways of processing as long as we are alive. (Click here for the story of a 66-year old grandmother whose lazy eye was fully corrected after three months of vision therapy!)
Vision therapy is highly successful in remediating a lazy eye. At least 95% of patients treated fully in office based vision therapy will have full resolution of their amblyopia! Much akin to other physical therapies, vision therapy stimulates and guides visual development, training the brain to perform visual functions that did not develop on their own. Vision therapy is prescribed by developmental optometrists who specialize in children's vision and who have received board certification in this area of care. The title of a pediatric optometrist who specializes in vision therapy is Fellow in the College of Optometrists in Vision Development, noted with the credentials of F.C.O.V.D. included in his or her professional title.
Office based vision therapy is highly successful in improving a lazy eye. Office based vision therapy corrects the cause of the brain's inability to align and use both eyes together, so the gains are permanent. 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.
Like other interventions, office based vision therapy usually involves patching the clear eye to force the blurry eye to work, but for much shorter periods of time. Much less patching time is necessary when the child's visual system is also being trained how to use the weak eye properly. By the end of therapy, the child's patching time has been eliminated altogether.
The gains achieved in vision therapy are permanent. This is because once the child's brain learns binocularity, or how to fuse the images from both eyes, the child's visual system is restored to normal. Binocular fusion is the glue which permanently holds the vision system in place, simply because it's easier to see correctly than to have each eye fighting each other to see separately. Binocular fusion keeps the eyes from drifting out of alignment, and because there is no longer a need for the lazy eye to suppress, its improved acuity, or sharpness of vision, is not lost over time.
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.
It is extremely important for children to develop equal vision in both eyes in order for them to function normally. Good sharpness of sight and two-eyed binocular vision are vital for children to succeed in school, sports, or any other activity that requires clear vision, good hand-eye coordination, and strong depth perception. When children with untreated amblyopia grow to be adults, their choice of career may be limited and, if they are unlucky enough to lose vision in their one good eye, they could be visually impaired or legally blind for life.
For these reasons, it is extremely important for parents to have their child’s eyes examined by an optometrist as early as possible so vision problems can be found and treated. Vision can be tested in infants and very young children, and it is recommended that a child be examined at least by the age of three.
However, if you are a parent of a child with a lazy eye who was diagnosed after age six, please do not be misled. There is help. If you need assistance locating a developmental optometrist who provides vision therapy in your area, call the national certifying board of the College of Optometrists in Vision Development at 1-888-268-3770 or visit their web site at http://www.covd.org. Also, your family optometrist can be a good resource. Ask if he or she provides vision therapy or if they can make a referral to a colleague who does.