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Strabismus, commonly referred to as crossed or wandering eyes, occurs when one or both eyes turns in or out, up or down. The condition is caused by the brain's inability to coordinate both eyes simultaneously. The brain is the master control center of vision, and somewhere early in a child's visual development, the brain failed to develop "binocularity," or the ability to use both eyes at the same time.  The condition usually develops before a child is two but can occur as late as age six.   It is important  that strabismus receive prompt treatment.   Children do not outgrow crossed eyes, and the condition can worsen over time.  Children with strabismus may develop additional complications with amblyopia, or "lazy" eye.  (Note: It is common to see infants younger than three months cross their eyes as they are learning how to team and coordinate their eye movements. This is normal and not a condition of true crossed eyes.)  

 

          

Strabismus in which the misaligned eye turns in or out is divided into two categories: esotropia ("crossed" eye) means an eye turns in towards the nose, and exotropia ("wandering" eye) means an eye turns out away from the nose. In addition, the eye turn may be constant or happen only at times, such as when the child is tired; it may be the same eye which always turns, or the left and right eyes may turn alternately. The child's eye may turn  only when he is looking at objects close up, or it may turn when looking both near and far. The degree of eye turn may be so great that it is readily noticeable, or slight enough that parents may fail to recognize there's a problem.

Because the brain has not learned to align the eyes and use them together, each eye aims independently of the other.  In other words, both eyes do not point at the same place at the same time. When each eye is looking at a different place, the brain receives two different "pictures." This would normally result in double vision. However, these children's brains learn to protect themselves from seeing double by suppressing, or "turning off" the crossed eye. The brain refuses to receive the visual input from the turned eye; children with a crossed or wandering eye only see out of one eye at a time. 

Suppression is the brain's learned adaptation that protects children from double vision, but it also causes them to lose depth perception, or the ability to judge distance. Children with strabismus do not see a three-dimensional world. Instead, their world appears much flatter without depth and distance judgments. With the loss of spatial judgment, children with strabismus are generally more clumsy and are ten times more prone to accidents because of their compromised visual system.

Older children and adults can develop a crossed eye after a head injury, stroke, or as the result of some diseases. When this happens and the onset of strabismus is later in life, these older children and adults will usually experience double vision. This is because by age of six the brain is already "wired" to use both eyes together and therefore can't ignore or "turn off" the image being received from the turned eye.

Various types of strabismic conditions are treated differently. For example, glasses will nearly always be prescribed for esotropia. The glasses help relax the crossed eye that is turning in too far, allowing it to aim straighter.  In very mild cases of crossed eyes this may be enough to correct the problem, but usually additional treatment is required. There are two different approaches to the treatment of strabismus: surgery and therapy.  

The Surgery Myth A close-up of ophthalmic surgery being performed to correct strabismus. (Photograph by Michael English, M.D. Custom Medical Stock Photo, Inc.)

Ophthalmologists, or eye surgeons, usually recommend surgery to correct strabismus.  However, strabismic surgery has some very real limitations: it will improve the eye's appearance, but rarely does it do anything to improve vision. The situation cannot be overstated: surgery for crossed or wandering eyes is by enlarge a cosmetic consideration with little or no affect on the eye's visual function.  In fact, the nerve damage and scar tissue that result may permanently reduce the child's chances of achieving normal two-eyed vision later on through therapeutic remediation.

Parents often have common misconceptions about eye surgery. One of the most frequent misconceptions is that strabismus is caused by "weak" eye muscles. This is simply not true, but it's an easy way for doctors to explain the problem, however oversimplified and inaccurate. With the exception of muscle paralysis, the eye muscles in a crossed or wandering eye are not weak.  The problem is not muscular, but neuromuscular; the problem lies in the signal from the brain to the muscles which control eye alignment. Strabismus is the result of faulty coordination between the brain and eye muscles--in other words, strabismus is a brain-based problem.  

A simple procedure can demonstrate that there is nothing inherently wrong with the eye muscles in a crossed eye. Place your finger in front of the child and have him look at it. Now cover the straight eye with your other hand and watch the crossed eye. It immediately straightens. The muscles in the crossed eye automatically aim the eye without difficulty. The real problem is not weak muscles, but the inability of the brain to control the muscles in both eyes at the same time--in other words, faulty signals from of the brain to the two eyes together.

The recommendation for strabismic surgery is often oversimplified, such as "the weak eye muscles must be operated upon to realign the eye and correct the problem." There are two large fallacies in this recommendation: 1) Since weak muscles aren't the true cause of strabismus, then surgical intervention is addressing only a symptom, not the underlying cause. 2) In the vast majority of cases, surgery does not "correct" the child's inability to use both two eyes together; it only cosmetically aligns the eyes so they look straight. 

For any parent of a child with strabismus, it is imperative that they educate themselves and realistically understand the limitations of surgery.  Eye muscle surgery to correct strabismus concerns itself only with making the eye appear straight--a cosmetic "fix" but not a visual cure.   In fact, the surgical standard to determine a successful outcome of the surgery is based on appearance.  Ophthalmologists consider a surgery "successful" if afterwards the eyes are aligned within ten degrees of each other with no consideration given to improvement in vision.  That's not their goal.  Why?  Because surgery does not usually improve visual function.  Surgery deals only with extraocular muscles, not the brain and it's visual processing pathways.  Surgery simply cannot correct the nerve pathways from the brain to the eye which caused the crossed eye to begin with.  Surgery does nothing to train the brain how to use both eyes together. Instead, the process of invasive surgery and resulting scar tissue only compounds the real problem, making later nonsurgical intervention much more difficult.

Most children who have undergone surgery for a crossed eye still suppress one eye full time. Suppression is the brain's learned response to avoid double vision. Suppression must be unlearned and the brain trained to use both eyes together if normal functional vision is to be restored. Less than 20% of children who undergo eye surgery for a crossed eye eventually achieve binocular fusion (two-eyed vision) with normal depth perception and visual function. The few who do are nearly always very young children whose visual systems were still developing and fluid enough to fall into binocularity on their own. This is not true for the vast majority, however. Over 80% of surgery patients still live in a monocular, one-eyed world without depth and distance judgments.  

Children with exotropia, or a wandering eye that floats out from the nose, fair a little better with surgery.  Children whose eye turns out only occasionally have the best clinical results from surgery.  About 1/3 can achieve normal vision afterward--but 2/3 do not!

Unfortunately, because the eye looks straight after surgery, most parents do not realize their child's vision hasn't improved at all.  And because the real cause of strabismus was not addressed, the cosmetic results of surgery are often not permanent. Over time, the eye begins to turn again and repeated operations are required to realign the eye.

There is a better alternative.  

Vision Therapy

Unlike surgery, vision therapy addresses the real cause of strabismus. Therapy improves the coordination between the brain and eyes, eliminates suppression, and teaches the brain how to use both eyes together so that the eyes remain straight. By treating the underlying cause of strabismus, vision therapy restores normal vision. Therapy corrects the child's vision system by teaching the eyes how to aim together and training the brain to receive and fuse the visual images from both eyes at the same time. Ninety percent (90%) of therapy patients complete treatment with eyes which are straight and a visual system which operates normally. Most importantly, because binocular fusion (two-eyed vision) is the "glue" which holds the eyes straight, the results are permanent.  

One of our patients before treatment

After five months of vision therapy

constant right eye turn, full suppression     

eyes straight, no suppression, full binocularity

   

                   
Why, then, when therapy is so effective in curing strabismus is surgery so often recommended? Part of the answer lies in the "David and Goliath" syndrome. There are more than 12,000 eye surgeons. Their job is to perform surgery. By no means are eye surgeons, or ophthalmologists, to be discredited. Theirs is an important job, and the surgeries they perform--from cataract removal to refractive laser surgery--improve the quality of their patients' lives. However, American ophthalmologists have no training in vision therapy and have only a very limited knowledge in functional vision remediation. When it comes to strabismus, the only treatment that ophthalmologists have with their surgical background is operating on the eyes to make them appear straight. (This is not true in Europe. European ophthalmologists have much more extensive training in functional vision training, and therapy is nearly always recommended before surgery.)  

The number of American doctors specializing in vision therapy, on the other hand, is much smaller. There are less than 1,600 developmental optometrists specializing in vision therapy. These doctors are Fellows or Associates in the College of Optometrists in Vision Development, the national certifying organization for doctors who specialize in vision therapy.  All Fellows have passed a rigorous national board to receive their certification in the remediation of binocular vision problems. Because of their training and background, C.O.V.D. Fellows are functional vision specialists with the knowledge and expertise to fully correct strabismus. But because their numbers are so much smaller nationwide, so is their patient base.

One of the reasons that there are so few eye doctors specializing is vision therapy is economics. Therapy is not as time efficient and economically rewarding for doctors as surgery. In addition, maintaining the staff, treatment space, and time required to commit to extended therapy can consume a large part of an optometrist's practice. Those doctors who commit themselves to providing vision therapy do so out of a sincere desire to offer their patients the best care possible.

 

Final Word

In the end, parents must make an informed decision about which type of treatment option they will pursue. If your child has strabismus, the best advice is to educate yourself on the pros and cons of each option. Make an appointment with both a surgical ophthalmologist and a developmental optometrist who provides vision therapy. Be proactive. Ask questions: Does what you've been told make sense? Does it seem reasonable? What are the risks of the treatment being proposed? Did you get all your questions answered by the doctor? In the end, parents must formulate treatment goals and carefully consider their options when entrusting their child's vision to any eye care professional. 

 

If you need help locating a developmental optometrist who provides vision therapy, you can call the national certifying board of the College of Optometrists in Vision Development at 1-888-268-3770 toll free 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.