Strabismus
Strabismus
Why Do People Have Strabismus?
How Do Six Muscles in Each Eye Work as One?
How Do Doctors Diagnose Strabismus and Amblyopia?
Strabismus is a condition in which the eyes cross or do not work together normally, which may lead to permanent loss of vision in one eye.
KEYWORDS
for searching the Internet and other reference sources
Amblyopia
Ophthalmology
Optometry
Vision
When people cross their eyes, the world suddenly doubles. Images, like the words on this page, become blurred, and it appears as if there are two of everything. When the eyes function correctly, they work together to focus images and to allow the brain to develop a three-dimensional view of the world. But when the eyes cannot work together, as when people cross their eyes, the brain sees two of everything. The result is double vision.
Fortunately, both eyes work together for most people. But some people have an eye disorder that causes the eyes to fail to line up properly, resulting in blurred or double vision. This condition is called strabismus (stra-BIZ-mus), which comes from a Greek word that means squinting. Often in strabismus, one eye may remain straight and the other eye may turn in, as if the person is crossing one eye.
Why Do People Have Strabismus?
Strabismus usually develops during infancy or early childhood. In most cases, there is no known cause, although sometimes several members of the same family have the disorder. This may mean that in some cases strabismus is inherited, like eye color. Other possible causes include:
- Farsightedness, causing focus difficulties
- Damage to one eye or to the part of the brain that controls the muscles involved in eye movement
- Other disorders that affect the brain, including Down syndrome, cerebral palsy, and hydrocephalus
- Less commonly, vision is blocked by a tumor* or cataract that causes cloudiness in the normally clear lens of the eye
- * tumor
- usually refers to an abnormal growth of body tissue that has no physiologic purpose and is not an inflammation. Tumors may or may not be cancerous.
Did Abe Lincoln Have Strabismus?
President Abraham Lincoln (1809-1865) is known for many things, from his work as a rail-splitter, to his legendary debates with Stephen A. Douglas, to serving as president of the United States during the Civil War.
Lincoln’s physical characteristics caused much discussion. He was unusually tall for his time, standing 6 feet 4 inches. He also was extremely thin for that height and probably weighed about 160 pounds when elected to Congress in 1847.
“He was not a pretty man by any means—nor was he an ugly one,” wrote William Herndon. “He was a homely looking man.” The assessment goes on and sounds extraordinarily harsh, considering that Herndon was Lincoln’s friend, law partner, and biographer.
Historical researchers have speculated that Lincoln had strabismus. In photographs, his eyes appear slightly off center. His right eye was thought to be abnormal, sometimes described by biographers as “wandering.” Researchers also believe that Lincoln may have had Marfan syndrome, a rare disorder that causes exceptional height in combination with especially long legs, hands, and feet. Eye trouble is another characteristic of the syndrome. Some of Abraham Lincoln’s descendants are known to have had Marfan syndrome, and it is known to be an inherited disorder.
Strabismus affects about 3 to 5 percent of children in the United States. It occurs in boys and girls equally. Fortunately, if it is diagnosed and treated early, there is a good chance of saving or improving vision in the affected eye.
Some adults have strabismus. This may be because they were not treated for it as a child, or because the treatment was not effective. Other adults may develop strabismus when a disorder such as stroke* causes the eyes to cross or not work together normally.
- * stroke
- may occur when a blood vessel bringing oxygen and nutrients to the brain bursts or becomes clogged by a blood clot or other particle. As a result nerve cells in the affected area and the specific body parts they control do not properly function.
How Do Six Muscles in Each Eye Work as One?
The eyes and the nerves that connect them to the brain work like the two lenses of binoculars. They merge the images seen by each eye into one image. Six muscles are attached to each eye, and they control how the eyeball moves left and right or up and down. To make it possible for the brain to develop a single three-dimensional image, the muscles must work together to focus, just as the two lenses of binoculars must be aligned to focus together.
People with strabismus have trouble with one or more of the muscles in an eye. Instead of working together, one eye is out of step. Sometimes strabismus seems to come and go, depending on how tired the eyes are, and sometimes the eyes remain out of step. There are different forms of strabismus:
- When one eye points inward toward the nose, which makes the person look cross-eyed, the condition is called “esotropia” (es-o-TRO-pe-a).
- When one eye points away from the nose, as if looking to the outside, the condition is called “exotropia” (ek-so-TRO-pe-a) or “walleye.”
- When the brain turns off the vision in the turned eye in favor of the vision in the straight eye, the condition is called “strabismic amblyopia” (stra-BIZ-mik am-blee-O-pee-a) or “lazy eye.”
Amblyopia does not mean that the eye is lazy. Instead, the brain turns off the image coming from the optic nerve in that eye so the person sees only one clear image of the world instead of having blurred or double vision.
A Little Pirate
Mrs. Apple noticed that the eyes of her baby Chloe often did not work together. She had read in a book how babies sometimes appear cross-eyed or how it seems one eye is looking off in another direction from the other. This can be normal for a very young baby. But when Chloe was about four months old, Mrs. Apple became worried. Chloe’s left eye seemed to be looking at her nose when Mrs. Apple moved her face close, and the right eye seemed to be looking straight ahead. Mrs. Apple took the baby to an ophthalmologist* for an eye exam and was told that Chloe likely had strabismus.
- * ophthalmologist
- is a medical doctor who specializes in treating diseases of the eye.
It is usually a parent who first notices the signs of strabismus when children are infants or preschoolers. The children are too young to complain about double or poor vision. If Mrs. Apple had not taken action because of her worries, the strabismus might have developed into amblyopia, leaving Chloe without vision in the crossed eye. Without treatment, amblyopia may become permanent.
Will Crossed Eyes Become Stuck?
It seems almost everyone has received this warning from a parent or teacher: “If you keep crossing your eyes like that, they could stay that way forever!”
Although the warning may be a way for parents to make children stop silly behavior, it is not medically true. Voluntarily crossing the eyes will not harm them or put them at risk of strabismus.
The ophthalmologist recommended that Chloe wear an eye patch over her normal eye. The doctor explained that this could force the weaker eye to develop vision more properly.
How Do Doctors Diagnose Strabismus and Amblyopia?
Diagnosis
Doctors use a variety of methods to diagnose strabismus and amblyopia. Most involve observation of how the child looks at objects, since most children are too young to recognize the letters on a standard eye chart. The doctor will cover one eye and then the other, holding and moving objects, and watching to see if the child squints or tries to cover or close one eye in favor of the other. The doctor also will check the alignment of the eyes by shining a light in both eyes to see if the reflection falls in the same place in the pupils (the black spot in the center of the eye) of both eyes.
Many children do not like to have their eyes covered during these exams. Some are frightened of the equipment that may be held close to their faces. New techniques under development use computers to track eye movements from a distance, sometimes while the child is watching a cartoon.
Treatment
The most common treatment of strabismus involves wearing a patch like Chloe’s over the stronger eye. The brain now starts to try to send and receive signals from the weaker eye, and the muscles that control it try to bring the eye back to a normal focus. The same result often is achieved with eye drops that blur the vision in the normal eye to make the other eye work harder. Doctors also may prescribe special eyeglasses for some children with strabismus. Some of these eyeglasses use prisms that change how the image is sent into the eye.
New techniques involve disabling or weakening one or more of the muscles in the eye. This is done to force the other muscles to work harder to bring the affected eye into focus with the normal eye. This can be done surgically by repositioning the eye muscles of one or both eyes. The operations can leave the eyes straight and vision normal, although sometimes the eyes appear straight but people still need eyeglasses to achieve good vision. Sometimes, injections are used to disable one or more eye muscles for a period of time. This may achieve similar results to surgery.
Treatment is most effective when children are young, which is why vision testing and early diagnosis are important. Strabismus and amblyopia do not simply go away, as some people believe. With treatment, children like Chloe can have almost normal vision and no restrictions on activities as they grow up.
See also
Cataracts
Farsightedness
Resources
Book
Ophthalmic Disorders Sourcebook, Health Reference Series, Vol. 17. Detroit: Omnigraphics Inc., 1997. Includes reports from government agencies and other groups about various eye disorders.
Organizations
American Academy of Ophthalmology, P.O. Box 67424, San Francisco, CA 94120-7424. The American Academy of Ophthalmology posts a fact sheet at its website about strabismus and amblyopia. Telephone 415-561-8500 http://www.eyenet.org/public/faqs/strabismus_faq.html
American Optometric Association, 243 North Lindbergh Boulevard, St. Louis, MO 63141. The American Optometrie Association posts a fact sheet about crossed-eyes and strabismus at its website, which also includes a Teachers’ Center and a Just for Kids! educational center. http://www.aoanet.org/cvc-crossed-eyes.html
Strabismus
Strabismus
Definition
Strabismus is a condition in which the eyes do not align in the same direction. It is also called crossed eyes or squint.
Description
With normal vision, both eyes focus on the same spot and send the brain the same message. This binocular fixation (both eyes looking directly at the same object) is necessary to see three-dimensionally and to aid in depth perception. When an eye is misaligned, the brain receives two different images. Young children learn to ignore distorted messages from a misaligned eye, but adults with strabismus often develop double vision (diplopia). A baby's eyes should be straight and parallel by three or four months of age. A child who develops strabismus after the age of eight or nine years is said to have adult-onset strabismus.
Esotropia is the most common type of strabismus. It occurs when the eyes turn inward. Infantile esotropia develops in children under the age of six months. Accommodative esotropia develops in children under age three who cross their eyes when focusing on objects nearby. This usually occurs in children who are moderately to highly farsighted (hyperopic). Congenital esotropia is a very rare form of strabismus that occurs with certain birth defects.
Another common form of strabismus is exotropia, sometimes called walleye, where the eyes turn outward. It may only be noticeable when a child looks at distant objects, daydreams, or is tired or sick. Other strabismus conditions include hypertrophia, where the eyes turn upward, and hypotropia, where the eyes turn downward.
With strabismus, in some cases the eye turn occurs always in the same eye; however, sometimes the turn alternates from one eye to the other. Most children with strabismus have comitant strabismus, which means that no matter where they look, the degree of deviation does not change. In incomitant strabismus, the amount of misalignment depends upon which direction the eyes are pointed.
False strabismus (pseudostrabismus) occurs when a child appears to have a turned eye; however, this appearance may actually be due to other factors:
- extra skin that covers the inner corner of the eye
- a broad, flat nose
- eyes set unusually close together or far apart
False strabismus usually disappears as the child's face grows. An eye doctor (ophthalmologist) needs to determine whether the eye turn is true strabismus or pseudostrabismus.
Demographics
Strabismus affects 5 percent of people in the United States or more than 12 million individuals, most of them children. Infantile esotropia affects about 1 percent of full term, healthy babies and a higher percentage of babies born prematurely or born with other facial defects. Congenital esotropia is rare but does not occur at a higher rate in premature babies. Strabismus occurs equally in boys and girls and shows no variation in racial or ethnic distribution. Most strabismus develops in young children, although a few diseases may cause it to develop in adults.
Causes and symptoms
Strabismus can be caused most often by a defect in the part of the brain that controls eye movement. It is caused less frequently by a defect in the muscles that control eye movement. It is especially common in children who have the following:
- brain tumors
- cerebral palsy
- Down syndrome
- hydrocephalus
- other disorders that affect the brain
Diseases that cause partial or total blindness can cause strabismus. So can extreme farsightedness, cataracts, eye injury, or having much better vision in one eye than the other.
The most obvious symptom of strabismus is an eye that is not always straight. The deviation can vary from day to day or during the day. People who have strabismus often squint in bright sunlight or tilt their heads to focus their eyes.
When to call the doctor
Parents should call their doctor whenever they notice their child's eyes appear misaligned, even if the child is very young. A baby whose eyes have not straightened by the age of four months should be examined to rule out serious disease. Strabismus is not a condition that a child will outgrow without medical intervention. Pediatricians can refer parents to an ophthalmologist (eye specialist) skilled in evaluating the vision of very young children.
Diagnosis
Every baby's eyes should be examined by the age of nine months. A pediatrician, family doctor, ophthalmologist, or optometrist licensed to use diagnostic drugs uses drops that dilate the pupils and temporarily paralyze eye-focusing muscles to evaluate visual status and ocular health. Early diagnosis is important. Some eye turns may result from a tumor. Untreated strabismus can damage vision and possibly result in lazy eye (amblyopia ).
Treatment
Preserving or restoring vision and improving appearance may involve one or more of the following:
- glasses to aid in focusing and straighten the eye(s)
- patching to force infants and young children to use and straighten the weaker eye
- eye drops or ointments as a substitute for patching or glasses or to make glasses more effective
- surgery to tighten, relax, or reposition eye muscles
- medication injected into an overactive eye muscle to allow the opposite muscle to straighten the eye
- vision training (also called eye exercises)
Prognosis
Early consistent treatment usually improves vision and appearance. The most satisfactory results are achieved if the condition is corrected as early as possible and before the age of seven.
Prevention
Strabismus cannot be prevented, but it can be corrected with early intervention.
Parental concerns
Parents are often concerned that eye turn is indicative of other vision problems. Sometimes strabismus does accompany other vision defects, so a complete eye examination by a pediatric ophthalmologist is advisable. Delay only increases the difficulty in correcting strabismus, so parents should not wait to see if their child outgrows the condition.
KEY TERMS
Amblyopia —Decreased visual acuity, usually in one eye, in the absence of any structural abnormality in the eye.
Ophthalmologist —A physician who specializes in the anatomy and physiology of the eyes and in the diagnosis and treatment of eye diseases and disorders.
Resources
BOOKS
Plager, David, et al. Strabismus Surgery: Basic and Advanced Strategies. Oxford, UK: Oxford University Press, 2004.
ORGANIZATIONS
American Academy of Ophthalmology. PO Box 7424, 655 Beach Street, San Francisco, CA 94120–7424. Web site: <www.aao.org>.
American Academy of Optometry. 6110 Executive Boulevard, Suite 506, Rockville, MD 20852. Web site: <www.aaopt.org>.
American Academy of Pediatric Ophthalmology and Strabismus (AAPOS). PO Box 193832 San Francisco, CA 94119. Web site: <www.med-aapos.bu.edu>.
WEB SITES
Cooper, Jeffrey. "All about Strabismus." Optometrist Network, 2001. Available online at <www.strabismus.org> (accessed October 31, 2004).
Gerontis, Corina C. "Exotropia, Congenital." Available online at <www.emedicine.com/oph/topic330.htm> (accessed October 31, 2004).
Ocampo, Vincente V., and C. Stephen Foster. "Exotropia, Infantile." Available online at <www.emedicine.com/oph/topic328.htm> (accessed October 31, 2004).
Stidham, D. Brian, and Chris Noyes. "Exotropia, Accommodative." Available online at <www.emedicine.com/oph/topic330.htm> (accessed October 31, 2004).
Tish Davidson, A.M. Maureen Haggerty
Strabismus
Strabismus
Definition
Strabismus is a condition in which the eyes do not point in the same direction. It can also be referred to as a tropia or squint.
Description
Strabismus occurs in 2-5% of all children. About half are born with the condition, which causes one or both eyes to turn:
- inward (esotropia or "crossed eyes")
- outward (exotropia or "wall eyes")
- upward (hypertropia)
- downward (hypotropia)
Strabismus is equally common in boys and girls. It sometimes runs in families.
Types of strabismus
Esotropia is the most common type of strabismus in infants. Accommodative esotropia develops in children under age two who cross their eyes when focusing on objects nearby. This usually occurs in children who are moderately to highly farsighted (hyperopic).
Another common form of strabismus, exotropia, may only be noticeable when a child looks at far-away objects, daydreams, or is tired or sick.
Sometimes the eye turn is always in the same eye; however sometimes the turn alternates from one eye to the other'.
Most children with strabismus have comitant strabismus. No matter where they look, the degree of deviation does not change. In incomitant strabismus, the amount of misalignment depends upon which direction the eyes are pointed.
False strabismus (pseudostrabismus)
A child may appear to have a turned eye, however this appearance may actually be due to:
- extra skin that covers the inner corner of the eye
- a broad, flat nose
- eyes set unusually close together or far apart
This condition, false strabismus, usually disappears as the child's face grows. An eye doctor needs to determine whether the eyeturn is true or pseudostrabismus.
With normal vision, both eyes send the brain the same message. This binocular fixation (both eyes looking directly at the same object) is necessary to see three-dimensionally and to aid in depth perception. When an eye is misaligned, the brain receives two different images. Young children learn to ignore distorted messages from a misaligned eye, but adults with strabismus often develop double vision (diplopia).
A baby's eyes should be straight and parallel by three or four months of age. A child who develops strabismus after the age of eight or nine years is said to have adult-onset strabismus.
Causes and symptoms
Strabismus can be caused by a defect in muscles or the part of the brain that controls eye movement. It is especially common in children who have:
- brain tumors
- cerebral palsy
- Down syndrome
- hydrocephalus
- other disorders that affect the brain
Diseases that cause partial or total blindness can cause strabismus. So can extreme farsightedness, cataracts, eye injury, or having much better vision in one eye than the other.
In adults, strabismus is usually caused by:
- diabetes
- head trauma
- stroke
- brain tumor
- other diseases affecting nerves that control eye muscles
The most obvious symptom of strabismus is an eye that isn't always straight. The deviation can vary from day to day or during the day. People who have strabismus often squint in bright sunlight or tilt their heads to focus their eyes.
Diagnosis
Every baby's eyes should be examined by the age of six months. A baby whose eyes have not straightened by the age of four months should be examined to rule out serious disease.
A pediatrician, family doctor, ophthalmologist, or optometrist licensed to use diagnostic drugs uses drops that dilate the pupils and temporarily paralyze eye-focusing muscles to evaluate visual status and ocular health. Early diagnosis is important. Some eye turns may be a result of a tumor. Untreated strabismus can damage vision in the unused eye and possibly result in lazy eye (amblyopia ).
Treatment
Preserving or restoring vision and improving appearance may involve one or more of the following:
- glasses to aid in focusing and straighten the eye(s)
- patching to force infants and young children to use and straighten the weaker eye
- eye drops or ointments as a substitute for patching or glasses, or to make glasses more effective
- surgery to tighten, relax, or reposition eye muscles
- medication injected into an overactive eye muscle to allow the opposite muscle to straighten the eye
- vision training (also called eye exercises)
Prognosis
Early consistent treatment usually improves vision and appearance. The most satisfactory results are achieved if the condition is corrected before the age of seven years old.
Resources
ORGANIZATIONS
American Academy of Ophthalmology. 655 Beach Street, P.O. Box 7424, San Francisco, CA 94120-7424. 〈http://www.eyenet.org〉.
American Academy of Pediatric Ophthalmology and Strabismus (AAPOS). 〈http://med-aapos.bu.edu〉.
American Optometric Association. 243 North Lindbergh Blvd., St. Louis, MO 63141. (314) 991-4100. 〈http://www.aoanet.org〉.
strabismus
strabismus
stra·bis·mus / strəˈbizməs/ • n. abnormal alignment of the eyes; the condition of having a squint.DERIVATIVES: stra·bis·mic / -mik/ adj.