Strabismus, the medical term used when the two eyes are not straight occurs in approximately 2% to 4% of the population.
There are three common types of strabismus:
Crossed eyes: A child may be born with this condition, or it may develop within a few months of birth or around age 2 years. This is also called esotropia, or convergent strabismus.
Walleye, or divergent eyes: A child may be born with this condition, or it may develop later. This is also called exotropia, or divergent strabismus.
Causes of Strabismus
The eyes are out of alignment vertically.
Most commonly, a tendency to have some type of strabismus is inherited. Sometimes the condition is due to the eyes being out of focus and the need for eyeglasses or, occasionally, to some muscle abnormality. Very rarely, strabismus may be secondary to a serious abnormality inside the eye, such as a cataract or tumor.
Defective binocular vision: The eyes need to be straight for fusion in the brain of the images of the two eyes. This gives accurate vision and stereopsis, or 3–D vision. 3–D vision is one of the ways used to judge depth.
Loss of vision in the turned eye: Loss of vision in one eye may occur in strabismus, especially under the certain circumstances.
One such circumstance is if a child is born with straight eyes, but one eye turns in around age 2 years. If this condition is not treated urgently, vision may be reduced to partial sight (legal blindness) in the turned eye. If treatment is begun immediately, however, perfect vision can often be restored.
Another situation where loss of vision may occur is when the eyes are unequally focused. If one eye is way out of focus with the other, the brain may ignore the image from the eye that is improperly focused. This prevents development of normal vision in the affected eye. This condition is sometimes called a “Lazy” eye, or amblyopia.
The aim of treatment is to restore good vision to each eye and good binocular vision. Treatment usually includes patching the eye that is always straight to bring the vision up to normal in the turned eye. Glasses may be used, particularly for eyes that are out of focus. Glasses may also help straighten the eyes. Surgery on the eye muscles is sometimes necessary.
The results of treatment are good and may be excellent, but may depend on how quickly treatment is begun. This applies particularly to children who are born with straight eyes but manifest a turned eye around age 2 years. If treatment is unduly delayed, vision may not be restored. This type of legal blindness can be completely prevented. Do not delay if your child has strabismus. Seek professional advice from your family doctor.
Your child is especially at risk
If any members of your family have had strabismus, the condition is more likely to develop in your child. Even if the eyes appear to be straight, the child should be examined by an ophthalmologist–a medically qualified eye specialist–by the age of 1 year. It is possible to examine a child of any age for strabismus and determine whether the eyes are properly focused. If you are not sure whether your child’s eyes are straight, consult your family doctor, who may advise referring the child to an ophthalmologist.