Strabismus (Crossed Eyes)

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Strabismus, or crossed eyes, is a vision condition where both eyes do not focus on the same object at the same time. It occurs when the eye turns in, out, up or down and is caused usually by weak eye muscle control and a high degree of far-sightedness (hyperopia).

Maintaining correct eye alignment is necessary to avoid seeing double, for good depth perception and to prevent the development of poor vision in a turned eye. The brain receives two different images from misaligned eyes, which may lead to double vision and confusion initially. Later the brain will ignore the image from the turned eye which, if not treated, can lead to permanent reduction of vision in the eye and a condition called amblyopia or lazy eye.

In infants and young children, strabismus usually develops most often by age 3, but older children and adults can also develop the condition.

There is also a common misconception that a child with strabismus will outgrow the condition. In fact, strabismus is likely to get worse without treatment. Children older than four months, whose eyes do not appear to be straight all the time, should be examined.

Strabismus is classified according to the direction the eye turns:

• Inward turning is esotropia
• Outward turning is exotropia
• Upward turning is hypertropia
• Downward turning is hypotropia

Other classifications of strabismus include:

• The frequency with which it occurs – either constant or intermittent
• Always involving the same eye – unilateral
• If the turning eye alternates between right and left – alternating.

What Causes Strabismus?

Strabismus is usually a condition caused by eye muscle problems, which include the transmitting nerves to the muscles or the control center in the brain that directs eye movements. But it can also develop due to other general health conditions or eye injuries.

Some risk factors that would make one susceptible to contracting strabismus include:

Medical conditions – people who have suffered a stroke or head injury, or who have Down syndrome and cerebral palsy, are at greater risk for developing strabismus.

Family history – people with parents or siblings who have strabismus are more likely to develop it.

Refractive error – people with a high degree of uncorrected far-sightedness (hyperopia) may develop strabismus due to increased eye focusing needed to keep objects clear.

There are many types of strabismus occurring in children and adults, but the two most common forms are accommodative esotropia and intermittent exotropia.

Accommodative esotropia usually occurs because of uncorrected far-sightedness (hyperopia). In far-sightedness, when the eye’s focusing system is linked to the system controlling where the eyes point, the added effort needed to maintain clear images may cause the eyes to turn inward. Symptoms of accommodative esotropia may include double vision, closing or covering one eye when doing close work, and tilting or turning the head.

Intermittent exotropia usually develops as an inability to co-ordinate both eyes. The eyes may have a tendency to point beyond the object being viewed. Symptoms may include headaches, difficulty reading, and eye strain. These patients also exhibit a tendency to close one eye when viewing at a distance or in bright sunlight.

How is Strabismus Treated?

There are several treatment options for strabismus to improve eye alignment and co-ordination:

Eyeglasses or contact lenses may be prescribed for patients with uncorrected far-sightedness. Patients with accommodative esotropia may only need this form of treatment and, once the far-sightedness is corrected, the eyes need less focusing effort and may remain straight.

Prism lenses are special lenses containing a prescription for prism power, which alter the light entering the eye and help reduce the amount of turning the eye does to look at objects. Sometimes the prisms can fully compensate for and eliminate the eye turning.

Vision therapy is a program of visual exercises to improve eye co-ordination and focusing ability. The treatment trains the eyes and brain to effectively cooperate. It remedies deficiencies in eye movement and focusing, and reinforces the eye-brain connection. Office-based as well as home training procedures may be prescribed.

Eye muscle surgery is undertaken to alter the length or position of the muscles round the eyes to improve alignment. The surgery may physically align the eyes so they appear straight. Vision therapy may be used in conjunction with surgery to functionally improve eye co-ordination and stop the eyes reverting to their previous condition of misalignment.

If you note symptoms of strabismus in you or your child, please see your optometrist for a comprehensive eye examination and treatment.