More commonly known as “crossed eyes,” strabismus is a disorder that causes the eyes not to line up in the same direction or look at the same object. With strabismus, the eyes can point in (esotropia, or crossed eyes), out (exotropia), up (hypertropia), or down (hypotropia). Strabismus can be classified as:
- Unilateral: the same eye always deviates
- Alternating: either eye deviates while the other remains fixed
- Constant: permanent misalignment
- Periodic: The eyes occasionally exhibit no signs of the condition
Approximately 4–5 percent of children are affected with this disorder. Treatment must be sought early in children, since strabismus cannot be outgrown. It should be noted that newborns often have crossed eyes when their vision is not yet developed. This will normally disappear as they grow.
Strabismus can lead to additional vision problems such as lazy eye (amblyopia). If a child has not outgrown strabismus by the age of four months, he or she should be examined for a proper diagnosis. Proper eye alignment is essential for good depth perception, preventing double vision, and preventing the development of poor vision in the turned eye.
Symptoms of Strabismus
The symptoms of Strabismus are:
- Eye movement that is not coordinated
- Poor depth perception
- Vision loss
- In children: the child may cover one eye, look at you with one eye closed, squint, or hold their head turned to one side.
- In adults: double vision, eye strain, headaches, or abnormal head positioning may occur.
What Causes Strabismus?
There are six muscles around the eye that work together, sending signals to the brain and directing eye movements so both eyes can focus on the same object. The muscles are divided into three groups: the muscles in the eyeball, the eyelid muscles, and the extra-ocular muscles, which rotate the eyeball within its orbit. In someone with this condition, the muscles do not work together due to an unequal pulling of muscles on one side of the eye or a paralysis of the ocular muscles. Other causes may involve the nerves that transmit information from the brain to the muscles or the part of the brain that directs eye movements. Eye injuries, head trauma, and other general health conditions can also cause strabismus.
As soon as symptoms appear, you should seek medical attention from an eye care professional. He or she will ask you questions about your medical history, family history, environmental factors that may contribute to the problem, and the symptoms you are experiencing. Your eye doctor will then perform an eye exam. Medical tests may include:
- Visual Acuity Exam: This exam measures the extent to which your vision may be affected. Typically, you are asked to read letters on reading charts at varying distances. Normal distance-vision acuity is 20/20.
- Refraction: This exam determines the lens power you need to compensate for any refractive errors you may have (such as nearsightedness, farsightedness, or astigmatism). In most cases, special instruments — a phoropter and a retinoscope — are used during this exam. Your eye care professional places a series of lenses in front of your eyes with a phoropter and measures how they focus light using a hand-held lighted retinoscope. Other times, your eye doctor will use an automated instrument that evaluates the refractive power of the eye. The power is then refined by your responses and determines which lenses allow the clearest vision.
- Alignment and Focusing: This exam looks for problems that prevent your eyes from focusing properly or make it difficult to use both eyes together. It checks how well your eyes work together, and how well they move and focus.
- Eye Health: This exam checks the structures of the eye to rule out any eye disease that may be causing or contributing to strabismus. Using various testing techniques, your eye doctor will assess the health of the eye.
Initial testing is done without the use of eye drops, so the doctor can see how your eyes respond under normal circumstances (eye drops temporarily prevent the eyes from changing focus). Once testing is complete, your doctor will be able to help you create a treatment plan if you have been diagnosed with strabismus.
If detected and treated early enough, strabismus is often correctable. Doctors have three main goals when treating this condition: obtain the best possible vision, gain the best eye alignments, and provide the best chance for binocular vision in both eyes. Treatment options for strabismus include:
- Eyeglasses or an eye patch can be used to cover the stronger eye and correct focusing imbalance
- Orthoptics (eye muscle exercises), which help to improve the eye muscles and straighten the eyes
- Vision therapy, which may involve exercises that help the brain and eye learn to work together
- Eye surgery
- Eyeglasses overlaid with thin plastic Fresnel prisms. Typically these are used prior to eye surgery in order to determine the amount of adjustment needed on the eye muscles.
- Botulinum toxin (Botox) injections are sometimes used on adults. Using a special needle, Botox is injected into an eye-turning muscle on the outside of the eye.
In most cases, early treatment for strabismus can correct the problem over a period of months or years. Without early treatment, permanent vision loss in one eye is possible. Typically, activities like driving are not affected. Safety glasses or goggles are recommended during sports or activities that entail risk of injury, such as welding or carpentry.
Risk Factors for Strabismus
Risk factors for strabismus include:
- Family history
- Refractive error
- Injury to eye
- Eye tumor
- Birth trauma
- Damage to fetal central nervous system
- Medical conditions
- In adults: stroke, brain tumor, thyroid disease, diabetes, myasthenia gravis, and other neurological diseases
If you have parents or siblings with strabismus, you are more likely to develop this condition, even later in life. People who have severe uncorrected farsightedness are at risk for developing strabismus due to the extra eye-focusing required to see clearly. Those who receive eye trauma may end up developing strabismus, especially if the eye muscles were damaged. Medical conditions such as Down syndrome and cerebral palsy also put a person at a higher risk due to the nature of the condition, which involves the brain, muscle movement, and body coordination.
Alternate Names for Strabismus
Crossed eyes; Squint; Walleye; Esotropia; Exotropia; Hypertropia; Hypotropia; Misalignment of the eyes; Comitant strabismus; Noncomitant strabismus
Questions to Ask Your Doctor
- Other than eyeglasses, what treatment options do I have?
- Which type of strabismus do I have?
- How will this condition affect my vision in the future?
- What are some of the complications I can expect in the future?
- How will this affect my depth perception, peripheral vision, and other visual abilities?
- How long will treatment last?
- U.S. National Library of Medicine, Strabismus, http://www.nlm.nih.gov/medlineplus/ency/article/001004.htm
- American Optometric Association, Strabismus (Crossed Eyes), http://www.aoa.org/x4700.xml
- Optometrist's Network, Strabismus, http://www.strabismus.org/