What is strabismus?
Strabismus (often called crossed eyes or squint) is a disorder that affects the eye muscles, causing the eyes to look in different directions and on different things at any one time. Either one or both eyes may look inwards, outwards, upwards or downwards. This misalignment may occur all or some of the time, and may affect the same eye always or alternate between the eyes.
How common is strabismus?
Strabismus is estimated to occur in up to 5% of children, although adults can also develop the problem.
What does strabismus do to eyesight?
Early in the disorder, people with strabismus experience double vision and confusion because the eyes are not focusing on the same thing. Eventually, the view from the ‘turned’ eye will be ignored (suppressed) by the brain as it tries to prevent seeing double. The view of the world is not three-dimensional; it lacks depth and distance. Left untreated, constant eye turning can result in reduced vision in the eye (or Amblyopia, also known as lazy eye).
What causes strabismus?
While strabismus tends to occur in children at a young age, it may also develop in older children and in adults. Complications and injuries to the eye muscle are causes of strabismus. However, strabismus frequently arises from defects in nerves that send signals to the eye muscles or in the part of the brain that controls eye movements. Strabismus is a heritable condition and therefore can run in families. It can occur in people with other disorders, such as Down syndrome and cerebral palsy, or who have had a stroke or head trauma. Strabismus may also arise in people who continually try to correct their far-sighted vision.
Testing for strabismus
Normally, it is advised that all children have their eyes examined at about nine months of age. However, regardless of age, advice should be sought for any notable eye problem.
A complete medical history of the patient is taken, including family history of eye problems and the patient’s general health, other diagnoses and medicines. Essential to the diagnosis, is a detailed history of the eye problem, such as when it began and the nature of the eye turning. For a confirmed diagnosis of strabismus, the eyes are given a thorough examination. This includes observing the eye parts, and tests for visual acuity, alignment, focusing, and refraction (lens strength).
How is strabismus treated?
Treatment of strabismus is necessary as it will not disappear with age and may worsen. Treatment aims to improve the alignment of the eye and enable the eyes to move in a coordinated fashion. It will depend on the characteristics of the condition.
Prescription eye glasses may be used to get rid of eye turn and other problems with vision, such as farsightedness. An eye patch can be worn over the ‘good’ eye to encourage the ‘lazy’ one to function properly. Prism lenses, which change the course of light entering the eye and reduce the extent of eye movement required for the eye to focus, can sometimes correct the problem. Lenses may be all that is needed when the condition is mild but, more often, vision therapy and/or surgery are also required.
Vision therapy aims to improve movement, coordination and focusing of the eyes. The series of eye exercises re-establishes normal vision by educating the eyes and the brain to function together, the eyes to move together, and the brain to effectively merge the images from both eyes into one. Vision therapy is very effective and the improvement is long-lasting.
Surgery performed on the eye muscles aims to align the eyes and make the turned eye appear straight. It involves altering the length or moving the eye muscles. Surgery improves the cosmetic appearance of the eye but may not correct vision, particularly if the problem is not with the eye muscles only. This means that vision therapy may also be recommended to coordinate eye and brain functioning.