Strabismus

What is Strabismus?

Strabismus is a condition in which the eyes do not align with each other. In other words, one eye turns in a direction that is different from the other eye.

Under normal circumstances, the six muscles that control eye movement work together and point both eyes at the same direction. Patients with strabismus have problems with controlling eye movement and cannot maintain normal ocular alignment (eye position).

Strabismus can be categorized depending on the direction of the poorly aligned eye:

Inward turning (esotropia)
Outward turning (exotropia)
Upward turning (hypertropia)
Downward turning (hypotropia)

Other factors to consider that help determine the cause and treatment of strabismus:

Did the problem come on suddenly or over time?
Was it present in the first 6 months of life, or did it occur later on?
Does it always affect the same eye, or does it switch between eyes?
Is the degree of turning small, moderate, or large?
Is it always present, or only part of the time?
Is there a family history of strabismus?

What are the types of strabismus?

There are several forms of strabismus. The three most common are:

Infantile esotropia: This condition is characterized by a large turn of both eyes inwards in infants that usually begins before the age of six months. Usually there is no significant hypermetropia and the glasses do not correctthe strabismus. Treatment of this type of strabismus is surgery on the muscles of one or both eyes to correct alignment.
Accommodative esotropia: This often occurs in cases of uncorrected farsightedness and a genetic predisposition (family history) for the eyes to turn in. Because the ability to focus is linked to where the eyes are pointing, the extra focusing effort needed to keep distant objects in clear focus may cause the eyes to turn inward. Symptoms include double vision, closing or covering one eye when looking at something near, and tilting or turning the head. This type of strabismus typically starts in the first few years of life. This condition is usually treated with glasses, but may also require eye patching and/or surgery on the muscles of one or both eyes.
Intermittent exotropia: In this type of strabismus, one eye will fixate (concentrate) on a target while the other eye is pointing outward. Symptoms may include double vision, headaches, difficulty reading, eyestrain, and closing one eye when viewing far away objects or when in bright light. Patients may have no symptoms while the ocular deviation (difference) may be noticed by others. Intermittent exotropia can happen at any age. Treatment may involve glasses, patching, eye exercises and/or surgery on the muscles of one or both eyes.

Adults may also experience strabismus. Most commonly, ocular misalignment in adults is due to stroke, but it can also occur from physical trauma or from childhood strabismus that was not previously treated or has relapsed or progressed. Strabismus in adults can be treated in a variety of ways, such as observation, patching, the use of prism on glasses and strabismus surgery.

How common is strabismus?

It is estimated that 4% of the population have strabismus.

What causes strabismus?

Most strabismus results from an abnormality of neuromuscular control of eye movement. Our understanding of these control centers in the brain continues to evolve. Less commonly, there is a problem with the actualeyemuscle. Strabismus is often inherited, with about 30 percent of children with strabismus having a family member with a similar problem.

Other conditions associated with strabismus include:

Uncorrected refractive errors
Poor eyesight in one eye
Cerebral palsy
Down syndrome (20-60% of these patients are affected)
Hydrocephalus (congenital disease leading to fluid accumulation in the brain)
Brain tumors
Stroke (the leading cause of strabismus in adults)
Head injuries, which can damage the area of the brain responsible for controlling eye movement, nerves that control eye movement and eye muscles
Neurological problems
Thyroid eye disease

When do the symptoms of strabismus appear?

By the age of 3 to 4 months, an infant’s eyes should be able to focus on small objects, and the eyes should be straight and well-aligned. A 6-month-old infant should be able to focus on objects both near and far.

Strabismus usually appears in infants and young children, and most often by the time a child is 3 years old. However, older children and even adults can develop strabismus. The sudden appearance of strabismus, especially with double vision, in an older child or adult could indicate a more serious neurologic disorder. If this happens, call your ophthalmologist immediately.

A condition called pseudostrabismus (false strabismus) can make it appear that a baby has crossed eyes when in fact the eyes are aiming in the same direction. Pseudostrabismus can be caused by extra skin covering the inner corners of the eyes and/or a flat nasal bridge.

How is strabismus diagnosed?

Anyone older than four months of age the agewho appears to have strabismus should undergo a full ophthalmological examination by a pediatric ophthalmologist, with extra time spent examining how the eyes focus and move. The examination may include the following:

Patient history (to determine the symptoms the patient is having, family history, general health problems, medications used and any other possible causes of symptoms)
Visual acuity (reading letters from an eye chart or examining the visual behavior of young children)
Refraction (checking the eyes with a series of corrective lenses to measure how they focus light).
Alignment and focus tests
Examination after dilation of the pupils to determine the health of internal eye structures

How is strabismus treated?

Treatment options include the following:

Eyeglasses or contact lenses: They are used in patients with uncorrected refractive errors. With corrective lenses, the eyes will need less effort to focus and may remain straight.
Prismatic lenses: Special lenses that can bend the light entering the eye and help reduce the amount of turning the eye must do to look at objects.
Orthopticexercises (eye exercises): May work on certain types of strabismus, especially in convergence insufficiency (a form of exotropia).
Medications: Eye drops or ointments. Also, injections of botulin toxin type A (such as Botox) can weaken an overactive eye muscle. These treatments may be used with ,or in place of surgery, depending on the patient’s situation.
Patching: To treat amblyopia (lazy eye), if the patient has it simultaneously with strabismus.
Eye muscle surgery: Surgery changes the length or position of the eye muscles so that the eyes are properly aligned. This is performed under general anesthesia with dissolvable sutures. Sometimes strabismus surgery with adjustable sutures is offered to adults, where the eye muscle positions are adjusted after the surgery.

What can happen if strabismus is not treated?

Some believe that children will overcome strabismus or that it will improve on its own. In fact, it can get worse if not treated.

If the eyes are not properly aligned, the following may result:

Amblyopia (lazy eye) or permanent poor eyesight in the eye with strabismus. When the eyes are looking in different directions, the brain receives two images. To avoid double vision, the brain can ignore the image from the turned eye, resulting in poor development of vision in this eye.
Blurry vision, which can affect performance in school and at work and enjoyment of hobbies and leisure activities
Eye strain
Fatigue
Headaches
Double vision
Poor three-dimensional (3-D) vision
Low self-esteem (from embarrassment about its appearance)

It is also possible that by not diagnosing strabismus, a serious problem (such as a brain tumor that causes the condition) can be overlooked.

What can be expected after treatment for strabismus?

The patient will need to see the Paediatric Ophthalmologist for follow-up to see if the patient has responded to treatments, and to make adjustments, if necessary.

In the case of children with strabismus, if the condition is caught in time and properly treated, it can result in excellent vision and depth perception and can protect against loss of vision.

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