What is strabismus?
Strabismus, although often referred to as “crossed eyes”, is actually the term used to describe any condition in which the eyes are not parallel—whether one eye turns or wanders in or out, or up or down. Strabismus may be present all the time, or it may only appear when a child is tired, ill, or concentrating on nearby objects. It may be obvious from birth, or it may not show up until later in childhood or even in adult life. Most often, strabismus is due to a persisting eye muscle imbalance.
It is not uncommon for a newborn baby’s eyes to wander. At birth, the eye muscles are not well-coordinated, but within a few weeks the infant learns to move both eyes together and the wandering disappears. However, if the condition continues beyond early infancy, prompt medical attention is needed to prevent amblyopia. Strabismus can run in families. Remember, some children can be born with strabismus and others develop strabismus as they get older.
What is amblyopia?
Amblyopia is poor vision in an eye that did not develop normal sight during early childhood. It is sometimes called “lazy eye”. When one eye develops good vision while the other does not, the eye with poorer vision is called amblyopic. Usually one eye is is affected. The condition is common, affecting 4 out of every 100 people. Amblyopia can sometimes be corrected only if treated during infancy or childhood.
Although newborn infants are able to see, vision improves over the first month of life as use of the eyes increases. During early childhood years, the visual system remains in a changeable state. Vision continues to develop with proper use of the eyes. However, if the eyes are not used to capacity, visual abilities decrease. After the first eight or nine years of life, the development of the visual system is complete and cannot be changed.
Causes and symptoms of amblyopia
Amblyopia is caused by any condition that affects normal use of the eyes and visual development. There are three major causes:
- Strabismus (misaligned eyes)
- Unequal focus (refractive error)
- Cloudiness in the normally clear eye tissues.
Amblyopia occurs most commonly with misaligned eyes such as crossing of the eyes. The crossed eye “turns off” to avoid double vision, becomes lazy or amblyopic, and the child prefers the better eye. Amblyopia may also occur when one eye is out of focus because it is more nearsighted, farsighted, or astigmatic than the other. The out of focus eye “turns off” and becomes amblyopic. Sometimes, in these cases the eyes can look normal but one eye has poor vision. This is the most difficult type of amblyopia to detect and requires careful measurement of vision. An eye disease such as a cataract (see cataract on home page) may lead to amblyopia. Any factor that prevents a clear image from being focused inside the eye can lead to the development of amblyopia in a child. Children may also inherit conditions from parents that cause amblyopia. Children in a family with a history of amblyopia or crossed eyes should be examined early in life.
It is important to understand that the treatment of the condtion that causes amblyopia does NOT cure the amblyopia. After straightening the crossed eyes, correcting the blurred vision with glasses, or removing a cataract, the doctor will then treat the amblyopia separately, if amblyopia is present. Amblyopia often goes unrecognized. A child may be unaware of having one good eye and one poor eye. Unless the amblyopic child has a crossed eye or other obvious abnormality, there may be nothing to suggest the child’s condition to the parents.
Amblyopia is detected by finding a difference in vision between each eye. Since measurement of vision is difficult in young children, the doctor often estimates visual acuity by watching how well a baby follows objects with each eye when the other eye is covered. The doctor observes the responses of the baby when one eye is covered. If one eye is amblyopic and the good eye is covered, the baby may attempt to look around the patch placed over the good eye or object to the patch. Poor vision in one eye does not always mean amblyuopia is present. Vision can often be improved with glasses. However, an examination of the interior of the eye is needed to check for other disorders which may be causing decreased vision.
To treat amblyopia, the child must be forced to use the lazy eye. This is usually done by patching or covering the good eye, often for weeks or months. Part-time patching may be required over a period of years to maintain improvement even after vision has been restored. Glasses may be prescribed to correct error or imbalance in focusing. If glasses alone do not improve vision, then patching is necessary. Sometimes, amblyopia is treated by blurring the vision in the “good” eye with special eyedrops to force the child to use the amblyopic eye. If an abnormality such as a cataract is discovered, surgery is required to correct the problem causing the amblyopia. After surgery, glasses, contact lenses or other methods can be used to restore focusing along with patching to improve vision. Amblyopia is usually treated prior to surgery for strabismus (misaligned eyes) and is sometimes needed after surgery as well.
The doctor can instruct parents about how to treat amblyopia, but it is a parental responsibility to carry out this treatment. No child likes to have a good eye patched, but parents must convince their child to do what will be best for them. Successful treatment mostly depends on parental interest and involvement, and their ability to gain their child’s cooperation. In most cases, it is the parents who play an important role in determining whether their child’s amblyopia is adequately treated.
How the eyes work together
The eye works basically like a camera. The movement of the eyes up and down and from side to side is controlled by six paired muscles attached to the outside of each eye. In order to see correctly, both eyes must face or turn together in the same direction. This is accomplished by teamwork: When the eyes turn, one muscle pair pulls, while another pair relaxes. The muscles are positioned in such a way that the eyes can move in all directions. To see correctly, both eyes must look at the same object at the same time. Each eye sees it from a slightly different angle, and each eye sends a slightly different picture to the brain. The brain takes these two pictures and blends them into one three-dimensional image. This brain fuction is called “fusion” and helps us to have depth perception or the ability to judge the relative distances between objects.
Sometimes, the eye muscles are not coordinated. The result is that the eyes cannot work as a team. If one eye is looking directly at an object while the other turns in or out, the image that the straight eye sends to the brain will be clear, but the image from the wandering eye will be blurry. Try as it might, the brain can’t blend these two images into one image (double vision). The child quickly and unconsciously learns to ignore the blurred image seen by the wandering eye (suppression). The result is that the stronger eye takes over most of the work of seeing and the weaker eye grows “lazy” (amblyopia) from lack of use.
My child doesn’t like to wear the patch!
Since the patch covers the good eye, your child will have trouble seeing at first. Naturally, many children try to take the patch off. This usually disappears as soon as the childs gets used to wearing the patch. You may be tempted to give in to an unhappy child, but remember that every time your childs remvoes the patch, effective treatment is delayed. You can help by being inventive. Some parents have found that if they wear a patch for the first few days, the child will wear one too. Try decorating the patch with a colorful design. Organize a game of pirates with your child as the captain or have family patch day. Patching their favorite doll, car toy, etc. can be helpful. Some children respond well to postive reinforcement rewards such as sticking gold stars on a chart each day the patch is worn.
For more information about joining “The Eye Patch Club”, see Prevent Blindness America by clicking here.
Most children are farsighted but most children don’t wear glasses. This is because children have a remarkable ability to focus their eyes to correct the farsightedness themselves. One of the side effects of this excessive focusing abilty is the eyes tendency to turn inward much like the eyes normally cross inward slightly when looking at a very near object. In a farsighted child with crossed eyes, the glasses prescribed are not necessarily to improve vision but rather to relieve the eye of this focusing and secondarily decrease this tendency for the eyes to cross inward. Rather than the eye doing the focusing and causing the eyes to turn inward, the glasses relieve the eye muscles and the eyes are allowed to straighten. Sometimes glasses alone will successfully straighten the eyes. Sometimes, glasses will only partially straighten the eyes and surgery will be needed. In the case of amblyopia, patching may be used as well as glasses. Remember that glasses for the farsighted child are given to straighten the eyes, not necessarily to improve vision. They must be worn full time to be effective. Farsightedness often decreases with age and the child will likely need weaker and weaker glasses as they get older. Sometimes, glasses are not needed by the time the child is a teenager. However, if glasses are precribed to correct nearsightedness or astigmatism, they may always be needed to help the child focus.
Surgery is sometimes needed along with glasses and patching. The surgery has been shown to be safe and effective. By adjusting the tension of the outer muscles on one or both eyes, the eyes can be straightened. If surgery is done on an older child, the eyes can be made straight, but fusion will probably not be achieved. A small incision is made in the outer covering of the eye where the muscles are attached. The eye muscles are either weakened or strengthened with tiny stitches that eventually absorb and do not need to be removed. The child is usually very comfortable after surgery. Pain pills etc. are usually not required and no patches are used for the surgery itself. The average surgery might take 30-45 minutes. One operation usually fixes the problem. However, the amount of correction that is just right for one child may be too much, or too little, for another. It is always possible that more than one operation may be needed. If glasses were needed before surgery, most likely they will still be needed after surgery. Surgery will help straighten your child’s eyes, but it is only one tool of treatment, not a complete cure. Sometimes, patching for amblyopia is also necessary after surgery.
Why can’t my child have surgery instead of wearing glasses?
Surgery is intended to correct only the amount of strabismus that glasses won’t take care of. Remember that your child’s eyes will be developing further, and that glasses for farsightedness will probably not be needed years from now. If too much surgery is performed at a young age, by the time your child is a teenager, the eyes could begin to turn the opposite way.