By Sandra M. Brown, M.D.
What Is Strabismus?
Strabismus is a condition in which each eye points at a different object (the eyes are misaligned). There are many different types of strabismus. They are named by the direction of the misalignment.
Cause of Strabismus
It is natural to think that strabismus is a problem with the eye or the eye muscles. However, in 90% of all children with strabismus, strabismus is a problem caused by the brain.
In the normal case, each eye is "aimed" at the object that the child wants to see most clearly. One area of the brain is responsible for keeping both eyes aligned on this object. This does not mean that the eyes are always pointed straight ahead.
Child wants to look at house. Both eyes are moved to the left, and both are aimed at the house.
In some children, there is a problem with this very delicate part of the brain. The eyes are healthy and the eye muscles work correctly, but the brain makes mistakes in how it sends signals to the eye muscles. The result is misaligned eyes. This problem appears in a variety of ways. Some babies are born with very crossed eyes. Some children have straight eyes for several years but develop crossed eyes later, generally between 18 months to 3 years old. Some children will have one eye wander outward, especially when tired. Although these conditions seem very different, the children all have the same underlying problem with brain control of the eye position. This condition very often runs in families.
Unfortunately, we cannot correct the brain problem to "cure" strabismus. We can improve the strabismus using treatments that help the brain to improve its own ability to control both eyes at the same time.
Strabismus treatment is very different depending on your child's particular situation. In some cases, surgery is the first treatment. In other cases, glasses or eye drops may be used first. Surgery may be necessary in addition to glasses or eye drops. This surgery is performed on the eye muscles to tighten or loosen them so that the unbalanced signals from the brain are compensated for by the new position of the eye muscles.
It is important to remember that all of these treatments can only help the brain. The success of any therapy for strabismus depends mostly on how well the brain responds to the treatment and re-learns to control the position of both eyes at the same time. For example, some children can be given glasses to help them focus more easily and clearly; their brains need just a little help, and will quickly take excellent control of eye alignment once the glasses are prescribed. The brains of other children have very little ability to control the eye position. In this case, surgery is often needed. The long-term success of surgery depends on how much the brain takes control and "fine-tunes" the eye position after the operation. This is why some children need more than one eye muscle surgery, and why adults who have had eye muscle surgery as children can need additional eye muscle surgery.
The Difference between Strabismus and Amblyopia
Amblyopia is the medical term for poor vision that is due to not using one eye. For example, if your child's right eye always crosses inward, the brain will shut off the picture from that eye and only use information from the left eye. Over time, vision from the right eye becomes weak (somewhat like having an arm in a cast -- the arm muscles become weak from not being used, even though they are not injured). Even though the right eye is taking pictures and sending them to the brain, the brain is shutting the pictures out because the eye is pointed in the wrong direction.
Brain sees the tree with right eye. Brain shuts off picture of house from left eye.
In this case, the strabismus (crossed eye) caused the amblyopia. There are many other causes of amblyopia. Some people use the words "lazy eye" to describe childhood eye problems, but this is a poor term because to some people "lazy eye" means a misaligned eye, and to other people it might mean a malformed eye or a nearsighted eye.
It is critical to treat amblyopia at the earliest possible age; the earlier it is detected, the easier it is to treat. Amblyopia becomes harder to treat as the child nears 7 years old. Parents must understand that treating amblyopia comes first, and this treatment is NOT designed to correct the misalignment of the eyes but to strengthen the vision in the eye with amblyopia. Treatments for amblyopia include glasses, patching, and eyedrops. Eye muscle surgery has no effect on vision and does not correct amblyopia.
How You Can Help Your Child...
Keep all your scheduled appointments. Insist on full-time wear of glasses, and apply the patch or eyedrops as instructed by Dr. Brown. If you have any questions about the prescribed treatment, please do not hesitate to call our office.
Copyright Sandra M. Brown MD, May 22, 2005