Strabismus (Esotropia and Exotropia)
Definition | Symptoms | Treatment | Clinic Information
Definition
Strabismus is a visual disorder where the eyes are misaligned and point in different directions. This misalignment may be constantly present, or it may come and go. Sometimes, only one eye is affected — turning inward (esotropia), outward (exotropia) or downward — while the other eye is directed straight ahead.
Strabismus is a common condition among children. Normal alignment of both eyes during childhood allows the brain to fuse the two pictures into a single 3-dimensional image. Strabismus or abnormal alignment can block this normal binocular development and cause amblyopia or reduced vision in one eye. If vision is reduced, the brain of the child will only learn to recognize the stronger image and ignore the weaker image of the amblyopic eye. This will eventually cause a loss of depth perception and, if not treated before 6-7 years of age, can result in permanent visual loss in the affected eye. If strabismus develops in an adult, the patient will often experience double vision because the brain has been trained to receive images from both eyes.
The exact cause of the eye misalignment that leads to strabismus is not fully understood. 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 eye muscles must work together with the corresponding muscles of the opposite eye. The brain coordinates these eye muscles. A cataract or eye injury that affects vision can also cause strabismus.
In infants, it is often difficult to determine the difference between eyes that appear to be crossed and true strabismus. Young children often have a wide, flat nasal bridge and a fold of skin at the inner eyelid that tends to hide the eye when looking to the side, 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 the family doctor, pediatrician, or ophthalmologist at birth, 6 months of age, 3 years of age, and pre-school to detect potential eye problems while they can still be treated.
- Decreased vision
- Misaligned eyes
Treatment
The treatment goal for strabismus is to preserve vision, to straighten the eyes, and to restore 3-dimensional vision. If amblyopia is detected in the first few years of life, treatment is often successful. If treatment is delayed until later, amblyopia or reduced vision generally becomes permanent. Occlusive patching of the better seeing eye can force use of the amblyopic eye and improve vision. Depending on the cause of the strabismus, 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, including a 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 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 depends upon 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. 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 infection, bleeding, excessive scarring, and other complications that very rarely may lead to loss of vision.
Clinic Information
For more information, see the Pediatric Ophthalmology & Adult Strabismus Clinic and the complete Clinic Services listing of the U-M Kellogg Eye Center.
Update: July 31, 2008
