Turned eyes (strabismus)
Strabismus is the medical term for misalignment of the eyes two eyes that are not straight. It occurs in at least five per cent of the population. There are three common types:
- Esotropia, or 'crossed eyes': One eye is turned inward, toward the nose. A child may be born with this condition, or it may develop a few months after birth or around age two to three.
- Exotropia, often called 'wall-eye' in the past: One eye is turned outward, away from the nose. A child is rarely born with this condition. More often, it develops later.
- Vertical strabismus: The eyes are out of alignment vertically.
Strabismus can cause a couple of different vision problems:
- Defective binocular vision: The eyes need to be straight for the brain to combine the images seen by the two eyes into a single picture. This gives us 3-D vision, which allows us to judge depth. Any turn of the eye can interrupt 3-D vision. As well, if an eye turns in, it can reduce the total field of vision.
- Vision loss in the turned eye: When a child's eye is turned, he or she may end up with only partial sight in the turned eye. This condition is called amblyopia, or 'lazy eye.' This can also happen if the eyes are unequally focused.
Strabismus can run in families. Sometimes the condition is due to the eyes being out of focus; in this case, eyeglasses are part of the treatment. Sometimes there is a problem with the eye muscles or nerves. Strabismus can also be caused by a serious problem inside the eye, such as a tumour or a cataract, which leads to poor vision.
How is strabismus diagnosed?
A child can be checked at any age to see whether his or her eyes are properly aligned. If you are not sure whether your child's eyes are straight, ask your family doctor or a qualified eye care professional, who may refer you to an ophthalmologist.
All newborns should have their eyes checked in the hospital for visual problems, such as cataracts or lack of visual response. All children should have their vision checked by age three and a half to four and a half to detect common treatable problems such as strabismus, amblyopia or the need for glasses.
Is my child especially at risk?
If any member of your immediate family has had strabismus or amblyopia, it is more likely that your child will have it. In this case, even if your child's eyes seem straight, he or she should be examined by a qualified eye care professional by age one and again by age three. Premature birth, neurological diseases, and a family history of severe eye diseases are also reasons to have your child's eyes examined early.
How is strabismus treated?
The goal of treatment is for your child to have good vision in each eye, as well as good binocular (3-D) vision. If your child's strabismus has caused amblyopia, treatment will aim at bringing the vision up to normal in the 'lazy' eye first. Glasses may help for eyes that are out of focus, especially when one is much worse than the other. They may also help straighten the eyes. Surgery on the eye muscles may be necessary, especially when glasses are not enough to straighten the eyes.
The results of treatment can be excellent. How much your child's vision improves depends on how early in life and how quickly treatment was started. This is especially true for amblyopia and for strabismus that develops in a child who was born with straight eyes. If treatment is delayed too long, it may not be possible to completely restore your child's vision. This kind of vision problem can be effectively prevented, so it is important to seek professional advice as soon as possible.
© Copyright by the Canadian Ophthalmological Society