What Is Strabismus?
Strabismus is a visual disorder in which the eyes are misaligned and point in different directions. This misalignment may be constant or intermittent. When the eyes are misaligned, typically one eye will fixate on objects of interest while the other eye turns in (esotropia), out (exotropia), down (hypotropia), or up (hypertropia).
Often times the eye that is fixing on objects switches; that is, the misaligned eye will fixate and the previously fixing eye will become the misaligned eye. This alternation of deviating eye is often a good sign suggesting that the vision in each eye is equal. On the other hand, if the eyes do not switch fixation (one eye is constantly the fixating eye and the other eye is constantly the misaligned eye), then the fixating eye is favored and almost always has better vision.
Esotropia and exotropia are common conditions among children. Eye misalignment typically results in double vision in adults, but the developing brain in a child deals with the double vision by suppressing one of the images. Therefore, abnormal eye alignment in childhood blocks normal binocular vision development (as the brain learns to rely on only one image from the fixing eye).
Although the avoidance of double vision is beneficial in some regard, this adaptation by the developing brain is also detrimental because the ignored eye loses the ability to see perfect “20/20” vision – a condition called amblyopia. Amblyopia is decreased vision in a perfectly healthy and well-formed eye which occurs because of a loss of the connection between an eye and the brain during a critical period of vision development from birth to 8 or 9 years of age. Young patients with eye misalignment also typically have poor stereo or 3D vision and depth perception.
Strabismus in adults often results in double vision because the brain has been trained to receive images from both eyes. Adults with strabismus are not at risk of developing amblyopia because the connections between the eye and the brain are already formed and cannot be suppressed.
- Misaligned eyes
- Possibly also decreased vision
The symptoms described above may not necessarily mean that your child has strabismus; however, if you observe one or more of these symptoms, contact your child's eye doctor for a complete exam.
The causes of eye misalignment are various, and sometimes unknown. Potential causes include high farsightedness, thyroid eye disease, cataract, eye injuries, myasthenia gravis, cranial nerve palsies, and in some patients it may be caused by brain or birth problems. Six eye muscles control eye movement and are attached to the outside of each eye. Two muscles in each eye move the eye right or left while the other four muscles move it up or down and control tilting movements. To focus both eyes on a single target, all 6 eye muscles on each eye must work together with the corresponding muscles of the opposite eye. The brain coordinates these eye muscle movements.
Tests and Diagnosis
In infants, it is often difficult to determine the difference between true strabismus (misaligned eyes) and eyes that appear to be crossed. Young children often have a wide, flat nasal bridge and a fold of skin at the inner eyelid (epicanthal fold) that tends to hide the white sclera of the eye when looking in side gaze, thus causing the eyes to appear crossed. An ophthalmologist can readily distinguish true strabismus from the optical illusion called pseudo-strabismus which resolves spontaneously with growth during childhood development. Children should undergo vision screening by a family doctor, pediatrician, or ophthalmologist at birth, six months of age, three years of age, and pre-school to detect potential eye problems early while they can still be treated.
Treatment and Drugs
The treatment goal for strabismus is to allow for normal vision development, realign the eyes, prevent amblyopia (lazy eye), and attempt to restore stereo or 3-dimensional vision. If amblyopia is detected in the first few years of life, treatment is often successful. If diagnosis and treatment is delayed until later, amblyopia (reduced vision in one or both eyes caused by disuse) may become permanent. Occlusive patching of the better sighted eye can force use of the amblyopic eye and improve vision in the amblyopic eye. Depending on the cause of the strabismus or amblyopia, treatment may involve repositioning the unbalanced eye muscles, removing a cataract, or correcting other conditions that are causing the eyes to turn. After a complete eye examination, refraction and detailed study of the inner parts of the eye, an ophthalmologist can recommend appropriate optical, medical, or surgical treatment.
Early surgery is often recommended to correct strabismus in younger infants, who can then develop normal acuity and binocular (stereo) vision once the eyes are straightened. As a child gets older, the chance of developing normal sight and depth perception decreases. Crossed eyes can also have a negative effect on a child's coordination and motor skills, social interaction and self-confidence.
Strabismus surgery involves making a small incision in the tissue covering the eye, which allows the ophthalmologist to access the underlying eye muscles. The eyeball is never removed from the socket during this kind of eye surgery. Which eye muscles are repositioned during the surgery and by how much depends upon detailed measurement of the type of strabismus. It may be necessary to perform eye muscle surgery on one or both eyes. When strabismus surgery is performed on children, a general anesthetic is required; a local anesthetic is often an option for adults.
Eye muscle surgery is generally performed as an outpatient procedure in a hospital or a surgery center. Recovery time is rapid and the patient is usually able to resume normal activities within a few days. Following surgery, glasses or prisms may sometimes be needed to “fine tune” the result. Over-or-under correction can occur and further "touch-up" surgery may be needed. As with any surgery, eye muscle surgery has certain risks which include over or under correction of the strabismus, infection, bleeding, excessive scarring, and other complications that very rarely may lead to loss of vision.
Your Questions about Eye Muscle Surgery Answered
Christopher Gappy, M.D., pediatric ophthalmologist, answers the most commonly asked questions about eye muscle surgery.
- Topics include:
- What is eye muscle surgery?
- What eye conditions does eye muscle surgery correct?
- What home preparations will my child follow on the day before eye muscle surgery?
- Where will my child's eye muscle surgery be performed?
- Is eye muscle surgery an out-patient procedure and is it covered by insurance?
- What are the risks of eye muscle surgery?
- How long will it take for my child's eyes to heal?
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Reviewed by Monte A. Del Monte, M.D.