Strabismus (squint)

Strabismus, also known as having a squint, is an eye condition in which the eyes don't point in the same direction. Typically one eye turns inward, outward, up or down.

Strabismus is often diagnosed in young children, but it can develop in older children and adults too. Around one in 20 children have a squint (Source: Patient). People with strabismus often have a family history of the condition, but there is a wide range of causes.

It's natural to worry about your child having a squint. Fortunately, early diagnosis and treatment can help improve strabismus. Treatment can also help avoid other vision problems caused by having a squint, such as a lazy eye.

After the age of three months, if you notice your child has a squint, see your GP or optician. If necessary, they can refer you to an orthoptist, someone who works in the childrens' eye clinic who is specially trained to assess strabismus in children. You might also get a referral to an ophthalmologist.

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Strabismus symptoms

The symptoms of strabismus can differ in infants and children compared to adults. It's often parents who first notice the signs of a squint in their baby or child. Adults who develop a squint are likely to be aware of symptoms themselves.

In adults, the signs and symptoms can include:

  • Having eyes that are visibly misaligned (crossed eyes)
  • Double vision, seeing two different images
  • Other changes to vision such as blurriness and loss of depth perception
  • A pulling sensation at the eye
  • Eye strain and, in some circumstances, headaches
  • Having to tilt or turn your head to see clearly
  • Being told by others that they're not sure if you are looking at them

If you suddenly develop strabismus and have double vision, this can be a sign of an underlying condition that needs treatment. You should see your GP or optician to assess your symptoms.

Strabismus treatment

There are various treatment options for strabismus. Your ophthalmologist should advise you of the best treatment depending on the diagnosis. For example, if a child has a lazy eye due to a squint, this may need to be treated first, usually by wearing an eye patch or using eye drops.

What causes strabismus?

Strabismus can be due to a problem with the eye muscles, the nerves that send instructions to the muscles, or the part of the brain in charge of eye movements.

There are many different causes for these problems, but strabismus is often inherited. 30% of affected children have another family member with strabismus (Source: Archives of Ophthalmology).

Conditions and risk factors that can result in strabismus:

  • A family history of the condition.
  • Uncorrected refractive errors, most commonly longsightedness (hyperopia), nearsightedness, myopia and astigmatism.
  • Underlying conditions including cerebral palsy, Down syndrome, and hydrocephalus (a build-up of fluid in the brain from birth).
  • Very rarely, strabismus can be due to a childhood eye cancer called retinoblastoma. This is rare, occurring in one in 20,000 births (Source: Patient), and your optician can rule this out.

Although most people with strabismus have it from childhood, it can develop in adults due to health problems and other causes, including:

  • Stroke, the leading cause of strabismus in adults (Source: Cleveland Clinic)
  • Brain tumours
  • Head injury
  • Graves' disease, a thyroid disorder

Types of strabismus

There are various types of strabismus. It is often described by the direction in which the affected eye turns:

  • Esotropia - inward turning
  • Exotropia - outward turning

Less commonly, the eye can turn up or down:

  • Hypertropia - upward turning
  • Hypotropia - downward turning

Strabismus can also be:

  • Intermittent
  • Constant
  • Unilateral (always affecting the same eye)
  • Alternating (sometimes affecting the left, sometimes the right eye)

When to get medical advice

Speak to your GP or health visitor if your baby appears to have either an intermittent or continuous squint after three months of age.

Children and adults should have their eyes tested regularly, and children get eye tests free with the NHS. Opticians can adjust eye tests for very young children. They'll be able to check for strabismus and any other eye conditions, such as refractive errors that could lead to a squint if untreated.

You can take your child for an eye test at a high street optician from around the age of three. Before then, speak to your GP or health visitor if you have any concerns about your child's eyes or sight, or call 111 for advice.

Living with strabismus

It's natural to feel worried about a strabismus diagnosis, whether for yourself or your child. You'll be dealing with treatment and adjusting to life with a condition that is often noticed by others. Some people feel self-conscious about having a visible difference.

It can help to talk to family and friends, so they understand how you're feeling. You can also speak with other people living with strabismus, and our Guide Line can help you find support groups.

Frequently asked questions

Medically reviewed by: The Royal College of Ophthalmologists on 18/10/2022

Edited by: Nick Astbury FRCS FRCOphth FRCP
Clinical Associate Professor

The Royal College of Ophthalmologists champions excellence in the practice of ophthalmology and is the only professional membership body for medically qualified ophthalmologists. The RCOphth is unable to offer direct advice to patients. If you’re concerned about the health of your eyes, you should seek medical advice from your GP, optometrist or ophthalmologist.

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