Strabismus - Crossed Eyes
What is strabismus?
Strabismus is a visual defect in which the eyes are misaligned and point in different directions. One eye may look straight ahead, while the other eye turns inward, outward, upward or downward.
You may always notice the misalignment, or it may come and go. The turned eye may straighten at times and the straight eye may turn.
Strabismus is a common condition among children. About 4% of all children in the United States have strabismus. It can also occur later in life.
It occurs equally in males and females. Strabismus may run in families. How ever, many people with strabismus have no relatives with the problem.
How do the eyes work together?
With normal vision, both eyes aim at the same spot. The brain then fuses the two pictures into a single three-dimensional image. This three - dimensional image gives us depth perception.
When one eye turns, two different pictures are sent to the brain. In a young child, the brain learns to ignore the image of the misaligned eye and sees only the image from the straight or better-seeing eye. The child then loses depth perception.Adults who develop strabismus often have double vision because the brain is already trained to receive images from both eyes and cannot ignore the image from the turned eye.
Amblyopia
Good vision develops during childhood when both eyes have normal alignment. Strabismus may cause reduced vision, or amblyopia, in the weaker eye.
The brain will recognize the image of the better-seeing eye and ignore the image of the weaker or amblyopic eye. This occurs in approximately half the children who have strabismus.
Amblyopia can be treated by patching the "good" eye to strengthen and improve vision in the weaker eye. If amblyopia is detected in the first few years of life, treatment is usually successful.
If treatment is delayed until later, amblyopia usually becomes permanent. As a rule, the earlier amblyopia is treated, the better the visual result.
What causes strabismus?
The exact cause of strabismus is not fully understood.
Six eye muscles, controlling eye move ment, are attached to the outside of each eye. In each eye, two muscles move the eye right or left. The other four muscles move it up or down and at an angle.
To line up and focus both eyes on a single target, all of the muscles in each eye must be balanced and working together. In order for the eyes to move together, the muscles in both eyes must be coordinated.
The brain controls the eye muscles. Strabismus is especially common among children with disorders that affect the brain, such as:
- Cerebral palsy
- Down syndrome
- Hydrocephalus
- Brain tumors
A cataract or eye injury that affects vision can also cause strabismus.
What are the symptoms of strabismus?
The main symptom of strabismus is an eye that is not straight. Sometimes children will squint one eye in bright sunlight or tilt their head to use their eyes together.
How is strabismus diagnosed?
Strabismus can be diagnosed during an eye exam. It is recommended that all children have their vision checked by their pediatrician, family doctor or ophthalmologist (medical eye doctor) at or before their fourth birthday. If there is a family history of strabismus or amblyopia, an ophthalmologist can check vision even earlier than age three.
The eyes of infants often seem to be crossed. Young children often have a wide, flat nose and a fold of skin at the inner eyelid that can make the eyes appear crossed.
This appearance of strabismus may improve as the child grows. A child will not outgrow true strabismus.
An ophthalmologist can usually tell the difference between true and false strabismus.
How is strabismus treated?
Treatment for strabismus works to:
- Preserve vision
- Straighten the eyes
- Restore binocular (two-eyed) vision
After a complete eye examination, an ophthalmologist can recommend appropriate treatment.
In some cases, eyeglasses can be prescribed for your child. Other treatments may involve surgery to correct the unbalanced eye muscles or to remove a cataract. Covering or patching the strong eye to improve amblyopia is often necessary.
How is strabismus surgery done?
The eyeball is never removed from the socket during any kind of eye surgery. The ophthalmologist makes a small incision in the tissue covering the eye to reach the eye muscles.
Certain muscles are repositioned during the surgery, depending on which direction the eye is turning. It may be necessary to perform surgery on one or both eyes. When strabismus surgery is performed on children, a general anesthetic is required. Local anesthesia is an option for adults.
Recovery time is rapid. People are usually able to resume their normal activities within a few days. After surgery, glasses or prisms may be useful. In many cases, further surgery may be needed at a later stage to keep the eyes straight. For children with constant strabismus, early surgery offers the best chance for the eyes to work well together. In general, it is easier for children to under go surgery before school age.
As with any surgery, eye muscle surgery has certain risks. These include infection, bleeding, excessive scarring and other rare complications that can lead to loss of vision. Strabismus surgery is usually a safe and effective treatment for eye misalignment.
It is not, however, a substitute for glasses or amblyopia therapy.
Strabismus in Adults What is adult strabismus?
Strabismus is a condition in which the eyes are misaligned and point in differ ent directions. Most strabismus in adults has been present since childhood.
Strabismus which occurs in adults with out a history of childhood eye misalign ment should be carefully evaluated for medical or neurological causes such as:
- Diabetes
- Thyroid disease
- Myasthenia gravis
- Brain tumors
- Strokes
- Other neurological disorders..
In this form of strabismus, called Esotropia, the eye turns inward.
What are the symptoms of adult strabismus?
If the strabismus has been present since early childhood, the symptoms are usually minimal. If it develops later, the most common symptom is double vision. Some adults with strabismus will have:
Eye strain
- Discomfort when reading
- Headaches
- Abnormal head positions to use their eyes together.
In this form of strabismus, called Exotropia, the eye turns outward.
What causes double vision?
When your eyes are not aligned prop erly, each eye sees a different image. Infants and children can learn to suppress or ignore the image from one eye in order to avoid seeing a double image. Adults are unable to suppress one of the images, and therefore have double vision. This can be relieved by closing one eye, wearing a patch or aligning the eyes.
How is adult strabismus treated?
There is a common misconception that strabismus in adults is difficult or impossible to treat. Actually, adults with strabismus have many different treatment options including:
- Eye exercises
- Glasses with prisms
- Botulinum injections
- Eye muscle surgery, with or without adjustable sutures
Eye muscle exercises may be helpful in treating special problems such as convergence insufficiency, a condition in which the eyes are misaligned only for close work or reading.
Glasses with prisms are most useful for correcting small deviations. The images are realigned by prisms to compensate for the misalignment of the eyes, and the double vision may be relieved.
How does surgery work?
The most common treatment for strabismus at any age is surgery on the eye muscles. A tight muscle is surgically weakened by moving the muscle back on the eye. A weak muscle is tightened by removing a small segment of the muscle to shorten it. Surgery may involve the straight eye, the misaligned eye, or both.
What anesthetic is used in strabismus surgery?
Usually strabismus surgery is performed under general anesthesia. Sometimes surgery can be performed while the individual is awake or slightly sedated. In this situation, an injectable local anesthetic or anesthetic eyedrops are used.
What are adjustable sutures?
Adjustable sutures are a surgical technique that allows for some "fine tuning" of the alignment after surgery. The operation is performed in two stages.
In the first stage, one or more muscles are repositioned with "slip knot" sutures. In the second phase, usually performed within the next 24 hours, the muscle (s) may be repositioned by untying and retying the knots under eyedrop anesthesia. In many cases, no adjustment is needed and the slip knot is converted to a standard knot. Adjustable sutures require good cooperation from the patient and may not be suitable for everyone.
What are the risks of strabismus surgery?
The risks of strabismus surgery are extremely low, but as with all surgery there are potential problems. These may include:
- An unfavorable reaction to anesthesia
- Infection
- Reduced or double vision
- Inadequate eye alignment
Summary
An adult does not need to live with misaligned eyes. Glasses, prisms, exercises, and other treatments can sometimes help. Surgery can be done to:
- Align the eyes for cosmetic reasons
- Eliminate double vision
- Improve the use of the eyes together
- Reduce fatigue
Advances in surgical techniques allow an excellent chance of successful alignment and improved appearance for most individuals.
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Einstein Medical Inc., (c) 1999