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A lazy eye, technically referred to as amblyopia, means that one eye has not developed normally and always has blurred vision, 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. 


Common Causes of a Lazy Eye

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 more nearsighted or farsighted than the other, 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.  Because it's difficult to fuse a clear image with a blurry one, the brain learns vision is better if it suppresses the blurry eye that's interfering and just uses the clear one. The long-term suppression of the blurry eye causes vision to stop developing.  Once this type of lazy eye is discovered, treatment involves prescribing glasses or contacts to help equalize the vision in both eye.  Eye patching can help improve the sharpness of vision in the lazy eye, and vision therapy is often needed to establish binocularity and assist development of the compromised visual skills that didn't have a chance to develop on their own because of suppression.  (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.)


Treatment for a Lazy Eye

To correct amblyopia, the blurry eye must first be forced to work in order to allow the opportunity for clear vision to develop. This is usually done by patching the clear eye for specific periods of time, forcing the blurry  eye to "turn on" so that visual cells are stimulated, allowing clearer vision to develop. Secondly, glasses are prescribed to provide the blurry eye with the best support possible.  Finally,  if the underlying cause of the lazy eye is strabismus, then the eye turn must also be addressed.  

In addition to glasses, there are three different approaches to the treatment of a lazy eye:  1) patching alone,  2) patching combined with surgery, and 3) patching combined with vision therapy.   It is imperative that parents of a child with a lazy eye fully understand their treatment options so they can make the best choice for their child.

Patching Only

When the treatment procedure involves patching only, the child's clear eye is covered for 2 to 8 hours a day over a long period of time, from 3 months to a year. (Sometimes blurring drops are used instead of a patch.) By forcing the blurry eye to work, its vision improves.  However, there are serious drawbacks to this option.  First, because the good eye is covered, the child cannot see well and is often frustrated and uncooperative.  It becomes difficult for the parents to keep the patch on the child, especially if the doctor has recommended extended patching time.  Often the patch has to be taped over the child's eye to prevent him from removing it.  Over a period of time, the skin around the eye can become irritated and raw.  Also, there is danger of loss of vision in the clear eye when it is covered most of the time for weeks on end.   In the face of these hardships, patching often fails because the child and parents give up.  

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 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/patching.htm.  

Unfortunately, the gains from patching can be limited in the degree of visual improvement that can be achieved, and these gains are not always permanent.  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 acuity in the eye to begin with. Even if the family successfully makes it through the original patching ordeal and vision improves, it is not uncommon for the child to lose some of these gains over time.  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 a problem.  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.

Patching with Surgery

In addition to a patching regimen, eye surgeons sometime recommend surgery for the crossed/wandering eye. Unfortunately, eye surgery does nothing to restore normal two-eyed vision, a learned process of the brain.  Surgery simply makes the eyes appear straight by cutting and stretching muscles to reposition the eye, a cosmetic "fix" but not a visual cure. Surgery cannot correct the improper habits the brain learned which caused the misalignment problem to begin with, nor can surgery train the brain how to use both eyes together. Most children who have undergone surgery for a crossed eye still suppress one eye full time. In order for the problem to be truly corrected, the brain must learn not to suppress and be trained to use both eyes together. (For a more complete discussion on the limits of surgery to correct strabismus, see our web page "Crossed and Wandering Eyes.")

On average, less than 20% of children who undergo eye surgery eventually achieve normal two-eyed vision. The few who do are nearly always very young children under the age of six whose visual systems were still developing and fluid enough to fall into binocularity on their own.  

Misconceptions about the "Critical Stage" for Treatment

It is for this reason that some parents are told that a lazy eye can only be corrected when the child is very young, usually age six 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.   

While these doctors are well intentioned, they are wrong.  Eye doctors who believe that a lazy eye cannot be treated after age six simply lack the background and necessary training to correct a lazy eye in older children.   Because they are not schooled in the functional remediation of binocular vision problems, they do not have the training to treat older children.  A lazy eye can be treated at any age when glasses and patching are combined with vision therapy.  (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

Vision therapy is highly successful in remediating a lazy eye.  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 (sometimes called behavioral 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.    

Vision therapy is highly successful in improving the function and performance of a lazy eye.   Therapy corrects not only the poor vision in the lazy eye, but it also corrects the underlying problem 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.  Research shows that vision therapy restores the visual system to normal in over 90% of cases.  Even in the remaining 10% of cases, those most severe instances of lazy eye complicated by additional circumstances, therapy can improve the  child's vision to more functional levels.  And this can be done at any age.  (It should be noted, however, these statistics are for children who have never undergone surgery.  Scare tissue and nerve damage drops the success rate for a child who has already had one surgery to fifty percent, and the therapy prognosis for children who have had more than one surgery is poorer still.)  

Like other interventions, vision therapy usually involves patching the clear eye to force the blurry eye to work, but for much shorter periods of time.  Rather than full time patching for up to twelve hours a day, a patient in vision therapy will usually be asked to patch for two hours. 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.  


Final Word

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.  In Kansas, the "See to Learn" program sponsored by the Kansas Optometric Association allows every three-year-old to be checked for free. 

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.



The Children's Vision Information Network was created to raise public awareness about potential vision problems in children.  This site is not intended as a substitute for a complete eye exam and professional advice from your family optometrist.  Parents, teachers, occupational therapists, psychologists, and related professionals have permission to copy and distribute information contained in the site for educational purposes only with the condition that each page is copied in its entirety with the URL included (www.ChildrensVision.com).  All publishing rights are reserved. Direct specific inquiries to Mary Barton, Director of Vision Therapy, at (316) 722-3740 or email VTDirector@ChildrensVision.com.