What Is Strabismus?
Strabismus, also known as crossed or turned eye, is the medical term used when the two eyes are not straight. It occurs in approximately 2 to 4 percent of the population.
What Are the Different Types of Strabismus?
There are three common types of strabismus:
A child may be born with this condition, or it may develop within a few months of birth or around two years of age. 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.
The eyes are out of alignment vertically.
Turned or crossed eye
Head tilting or turning
Double vision (in some cases)
Even if a child's 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.
The ophthalmologist may use special tests, such as prism testing, to evaluate the alignment of the eyes.
Most commonly, a tendency to have some type of strabismus is inherited. If any members of your family have had strabismus, the condition is more likely to develop in your child.
Sometimes the condition is due to the eyes being far-sighted and the need for corrective 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 tumour.
What You Can Do to Reduce Risk
According to Joseph H. Calhoun, MD, Director, Pediatric Opthalmology & Strabismum, Wills Eye Hospital in Philadelphia, PA, "Any cause for poor vision in one eye in a child may lead to strabismum. There are many causes for poor vision in one eye, but a major concern of ophthalmologists is retinoblastoma, a malignant tumor of the retina. Although it is very rare, in the range of one in 20,000 children, this possibility is why every child with strabismus should have a pupil dilated examination of the retina as soon as strabismus is recognized."
And, to detect poor vision in one eye or the other, parents should take children for regular eye examinations. The American Academy of Ophthalmology recommends regular eye exams according to the following timetable:
Newborn to 3 months
6 months to 1 year
3 years (approximately)
5 years (approximately)
However, if you or your child notices problems with his or her vision, visit the eye doctor immediately.
What Happens to Sight in Eyes with Strabismus?
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 used to judge depth.
Reduction of vision in the turned eye (amblyopia)
A reduction of vision may occur in one eye in strabismus, especially under certain circumstances, such as late treatment.
One such circumstance is if a child is born with straight eyes, but one eye turns in around age two. 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.
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 and special drops (phospholine iodide) 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 two. 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.