What is strabismus?
Strabismus is a condition in which the eyes do not line up with one another. In other words, one eye is turned in a direction that is different from the other eye.
Under normal conditions, the six muscles that control eye movement work together and point both eyes at the same place. In patients who have strabismus, there are problems with the control of eye movement.
Strabismus can be classified by the direction of the turned eye:
- Inward turning, or "crossed eyes" (esotropia)
- Outward turning (exotropia)
- Upward turning (hypertropia)
- Downward turning (hypotropia)
Other factors to consider in cases of strabismus:
- Was the onset sudden or gradual?
- Was it present at birth (congenital), or did it occur later on?
- Does it always affect the same eye, or first one eye and then the other?
- Is the degree of turning small, moderate, or large?
- Is there a family history of strabismus?
What are the symptoms of strabismus?
There are many different forms of strabismus. The two most common are:
- Accommodative esotropia – This often occurs in cases of uncorrected farsightedness. Because the ability to focus is linked to where the eyes are pointing, the extra muscular effort needed to keep distant objects clear may cause the eyes to turn inward. Symptoms include double vision, closing or covering one eye when looking at something up close, and tilting or turning the head. The onset of this type of strabismus is typically in early childhood.
- Intermittent exotropia – The eyes tend to point beyond the object being viewed. Usually one eye will fixate on a target while the fellow eye is looking outward. Symptoms include headaches, difficulty reading, eyestrain, and closing one eye when viewing far away objects or when in bright light.
When do the symptoms of strabismus appear?
By the age of three to four months, an infant’s eyes should be able to focus on small objects and the eyes should be straight. A six-month-old infant should be able to focus on objects both near and far.
Strabismus usually appears in infants and young children up to age six, and most often by the time a child is three. However, older children and even adults can develop strabismus. The sudden appearance of strabismus, especially with double vision, in an older child or adult could signal a more serious neurologic disorder and should be evaluated urgently.
A condition called pseudostrabismus (false strabismus) can make it appear that a baby has strabismus when in fact the eyes are aiming in the same direction. Pseudostrabismus can be caused by extra skin covering the inner corners of the eyes, a wide nose, or eyes that are close together. As the baby’s face develops and grows, the eyes will no longer have the appearance of strabismus.
How common is strabismus?
Strabismus affects 2% to 5% of the U.S. population, or about 5 million to 15 million people.
What causes strabismus?
Strabismus occurs more frequently in families in which another family member has strabismus.
Other causes of strabismus include the following:
- Cerebral palsy (44% of these patients are affected)
- Down syndrome (50% of these patients are affected)
- Hydrocephalus (a congenital disease that results in a buildup of fluid inside the skull, damaging the brain)
- Brain tumor
- Uncorrected farsightedness
- Stroke (the leading cause of strabismus in adults)
- Head injuries, which can damage the area of the brain responsible for control of eye movement, the nerves that control eye movement, and the eye muscles
- Neurological problems
- Graves’ disease (overproduction of thyroid hormone)
How is strabismus diagnosed?
Anyone older than four months of age who appears to have strabismus should have a complete eye examination, with extra time spent on how the eyes focus and move. The exam may include the following:
- Patient history (to determine the symptoms the patient is having, family history, general health problems, medications being used, and any other possible causes of symptoms)
- Visual acuity (reading letters from an eye chart)
- Refraction (checking the eyes with a series of corrective lenses to measure how they focus light)
- Alignment and focus tests
- Tests to determine the health of internal and external eye structures
How is strabismus treated?
Treatment options include the following:
- Eyeglasses or contact lenses – Used in patients with uncorrected farsightedness. With corrective lenses, the eyes will need less focusing effort and may remain straight.
- Prism lenses – Special lenses that can bend light entering the eye and help reduce the amount of turning the eye must do to look at objects.
- Orthoptics or vision therapy – May work on some types of strabismus, especially intermittent exotropia.
- Eye exercises to help improve:
- coordination between brain and eyes
- eye movement
- eye focusing
- using both eyes together
- Medication – Eye drops or ointments. Also, injections of botulinum toxin type A (such as Oculinum or Botox) can weaken an overactive eye muscle. These treatments may be used with or in place of surgery, depending on the patient’s situation.
- Eye muscle surgery – Surgery can change the length or position of eye muscles so that the eyes are aligned correctly.
What can happen if strabismus is left untreated?
Some people mistakenly believe that children will outgrow strabismus or that it will get better on its own. In truth, it can get worse if not treated.
If the eyes are not properly aligned, the following may result:
- lazy eye (amblyopia) or permanent poor vision in the turned eye. When the eyes are looking in different directions, the brain receives two images. To avoid double vision, the brain may ignore the image from the turned eye, resulting in poor vision development in that eye.
- delayed development, such as walking and talking
- blurry vision, which can affect performance in school and at work, and enjoyment of hobbies and leisure activities
- double vision
- poor depth perception
- low self-esteem (because of a cosmetically displeasing appearance)
It is also possible that by not diagnosing and treating strabismus, a serious problem (such as a brain tumor that is causing the condition) may be overlooked.
What can be expected after treatment for strabismus?
The patient will need to see the physician for follow-up to note any response to treatments, and to make adjustments, if necessary.
If strabismus is caught in time and properly treated, it can greatly reduce the child’s suffering and protect against loss of vision.
- UpToDate. Evaluation and management of strabismus in children. www.uptodate.com. Accessed June 18, 2012.
- UpToDate. Patient information: Crossed eyes and lazy eye (The Basics). www.uptodate.com. Accessed June 18, 2012.
- American Association for Pediatric Ophthalmology and Strabismus. Strabismus. www.aapos.org. Accessed June 10, 2012.
- American Optometric Association. Strabismus (Crossed Eyes). www.aoa.org. Accessed June 10, 2012.