Strabismus (crossed eyes)

Strabismus is a condition where your eyes don’t line up or look at the same place at the same time. Commonly referred to as ‘crossed eyes’ as your eyes look in different directions. Strabismus usually occurs in people who have poor eye muscle control or who are very long-sighted (aka hyperopia).

What is strabismus?

Strabismus is when both eyes fail to maintain proper alignment, and work together as a team. It happens when there are neurological or anatomical problems that interfere with the control and function of the eye’s coordination muscles. The problem may start in the muscles, or in the nerves or vision centres in the brain that control binocular (both eyes working together, like a pair of binoculars) vision.

There are six eye muscles that control eye movement, and they must all work together to focus on a single image. One muscle moves the eye to the right, another to the left. With the remaining four muscles moving the eye up, down and at an angle.

When a pair of eyes don’t align, the straight or straighter eye becomes dominant. The strength of vision in the dominant eye will remain, as the eye and its connection to the brain are working as they should. However, the weaker or misaligned eye isn’t focusing as it should, and it’s connection to the brain doesn’t form correctly.



If your eyes aren’t aligned, one of three things could happen;

1. You will see double, as both eyes aren’t aimed at the same point.

2. One of the eyes can ‘turn off’ in the brain, to avoid double vision. This condition is called suppression and if left untreated, leads to a ‘lazy eye’ or amblyopia.

3. The brain can develop a new match with each eye so that bonding occurs, even though the eyes aren’t aimed at the same spot. This phenomenon is called anomalous retinal correspondence.

Causes of strabismus

Strabismus can be caused by problems with either the eye muscles, the nerves that send information to the muscles, or the control center in the brain that directs eye movements. It can also develop as a result of other eye injuries or general health conditions.

Risk factors can include:

Family history: if your parents or siblings have strabismus, you’ll be more likely to develop it also.

Refractive error: if you have uncorrected long-sightedness (hyperopia) you may develop strabismus, due to the additional focusing your eyes need to do, to keep objects clear.

Medical conditions: such as Down Syndrome and Cerebral Palsy, or if you’ve suffered a stroke or head injury, you’re at a higher risk for developing strabismus.

Type of strabismus

Many types of strabismus can develop in both children and adults, but the two most common types are:

Accommodative esotropia: often a result of uncorrected long-sightedness (hyperopia). The eye’s focusing system is connected to the control tower where the eyes point. People who are long-sighted need to put a lot more effort in focusing, to keep images clear and sharp. This may cause their eyes to turn inward.

Symptoms may include: seeing double, closing or covering one eye when doing close work or reading, and turning or tilting the head.

Intermittent exotropia: can develop when someone’s unable to coordinate their eyes together, meaning the eyes may point further than the object they’re looking at. 

Symptoms include: headaches, difficulty reading, eye strain. You may also close one eye when viewing at distance or in bright sunlight.

What are the symptoms of strabismus? 

Strabismus can be constant or intermittent. The misalignment may also always affect the same eye (referred to as unilateral strabismus) or the two eyes may take turns being misaligned (alternating strabismus). 

The primary sign of strabismus is a visible misalignment of the eyes, with: 

  • One eye turning in (known as esotropia)

  • One eye turning out (extotropia)

  • One eye looking up (hypertropia) 

  • One eye looking down (hypotropia)

  • Or one eye looking at an oblique angle

Large-angle strabismus: sometimes, strabismus is very noticeable. Other times it might only be noticed when a child is tired, for example or looking at something very closely. Typically, constant large-angle strabismus doesn’t cause symptoms such as eye strain and headaches, as there is virtually no attempt by the brain to straighten the eyes. Because of this, large-angle strabismus usually causes severe amblyopia in the turned eye, if left untreated.

Small-angle strabismus: less noticeable cases of small-angle strabismus are more likely to cause disruptive visual symptoms, especially if it’s intermittent or alternating. Some signs of small-angle strabismus include:

  • Headaches

  • Eye strain

  • Inability to read comfortably

  • Fatigue when reading

  • Unstable or “jittery” vision

If small-angle strabismus is constant and unilateral, it can lead to significant amblyopia in the misaligned eye. 

Both large-angle and small-angle strabismus can be psychologically damaging, and affect the self-esteem of children and adults with the condition, as it interferes with normal eye contact with others, often causing embarrassment and awkwardness.

The various types of Strabismus


Treatment options for strabismus include prescription glasses, prism lenses, vision therapy or eye muscle surgery. If strabismus is detected and treated early, it can often be corrected with fantastic results. 

There are a few options to improve eye alignment and coordination for strabismus, including:

- Prescription glasses or contact lenses. This may be the only treatment necessary for some patients and can be combined with vision therapy. If you or your child have intermittent or small-angle strabismus, it might be possible to improve eye alignment non-surgically, with these treatment options.

- Prism lenses: special lenses that are thicker on one side. The prisms alter the light coming into the eye and reduce how much the eye needs to turn to be able to see. Sometimes the prisms can eliminate eye turning altogether.


Vision therapy: trains the eyes and brain to work together better. Your optometrist may prescribe a program of visual activities and eye exercises to improve eye coordination and focusing, which can help problems with eye focusing, teaming and movement and reinforce the crucial eye-brain connection.

- Eye muscle surgery: will likely be considered if an eye is constantly turned out, and the above treatments haven’t corrected the eye. Eye muscle surgery can alter the length or position of the muscles around the eyes, so they appear straight. Often this is combined with vision therapy to improve eye coordination and stop the eyes from becoming misaligned again.

Book an appointment

Your optometrist will provide a tailored treatment plan for you or your child, based on their symptoms, test results, diagnosis and requirements. If you are worried about yours or your child's vision, please make an appointment today.


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Am I or my children at risk of getting strabismus? Genetics may play a role in developing strabismus. If you or your partner have strabismus, your children have a higher chance of developing it also. 

What is the most common age for strabismus? Strabismus usually develops in infants and young children by 3 years of age. But older children and adults can also develop it. People often believe that a child will outgrow the condition, but unfortunately this isn’t true. In fact, strabismus may only worsen without treatment. Please contact your optometrist if your child’s older than 4 months old and their eyes don’t appear to be looking straight all the time. We also have a program called InfantSee where we offer infants aged 6 months + free eye exams.


Can adults develop strabismus? It’s important to note, while strabismus often affects children in the early developmental years, it can sometimes develop in adults also, as a result of trauma, stroke, neurological conditions or disease.

What’s the difference between Strabismus and Lazy eye? Most people will automatically assume ‘Lazy eye’ when an eye crosses or turns outward. However, Lazy eye or amblyopia is when the vision in one eye is reduced due to the neural pathways from the eye to the brain not being properly formed. Amblyopia can be caused by strabismus, but the two are different conditions. . Strabismus is the condition where one or both eyes turn either inwards, outwards, upwards, downwards or at an oblique angle.