What Is Squint (Strabismus)?

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Squint, known medically as strabismus, occurs when instead of moving in tandem, each of the eyes points in a different direction. While one is focused in the correct direction toward an object, the other may move up or down or turn in or out instead.

This is pretty common, occurring in about one out of every 20 children. While it normally affects children under the age of 5, squint can also occur in adults. Overall, about 4% of the U.S. population, or about 13 million people, are impacted.

Child with strabismus (squint)

IvanJekic / Getty Images

Types of Strabismus

There are four categories of squint that can occur depending upon the direction of the non-forward-looking eye. These include:

  • Convergent squint (esotropia): The drifting eye turns inward while the other remains straight.
  • Divergent squint (exotropia): The squint eye moves outward while the other is focused straight ahead.
  • Vertical squint (hypertropia): The affected eye moves upward while the other looks straight ahead.
  • Vertical squint (hypotropia): The eye with squint looks downward, while the other focuses ahead.

The type of squint, however, is related to the particular form you or your child may have. Here are the possibilities:

  • Accommodative esotropia: This type of squint is usually noticed during the first few years of life. There is a genetic predisposition here that is linked to farsightedness that has gone uncorrected. Those with this are prone to having their eyes turn inward toward the nose due to redoubling efforts and strain to focus on things in the distance.
  • Intermittent exotropia: This type of strabismus can happen at any age. It involves one eye pointing outward while the other focuses on an object.
  • Infantile esotropia: With this form of squint, children younger than 6 months old are typically affected. These children’s eyes tend to turn inward whether the focus is on something up close or in the distance. Farsightedness does not seem to play a role here. While this may in the beginning only happen occasionally, it soon becomes constant.
  • Adult strabismus: This can happen at any point. Usually, this is caused by a stroke or physical trauma. However, in some cases, it may be linked to prior childhood squint that was undiagnosed or untreated and which has now reoccurred or gotten worse.

Symptoms

Apart from noticing that an eye appears to be turning, each form of squint may come with its own distinct symptoms, although not always.

Accommodative Esotropia

With accommodative esotropia, symptoms can include:

  • Double vision
  • Head tilting
  • Closing or covering one eye when focusing up close

Intermittent Exotropia

For intermittent exotropia, the following symptoms can occur:

  • Double vision
  • Headache
  • Straining of eyes
  • Reading difficulties
  • Closing one eye in bright light or when focusing far away

Infantile Esotropia

Other than a turning or a crossing of the eyes, usually there are no symptoms associated with this. There is generally no need for glasses or issues with double vision in these patients.

Adult Strabismus

Having an eye out of alignment is one telling symptom. If you have adult strabismus, you may also notice symptoms such as:

  • A feeling that your eye is being pulled in one direction or is suddenly weak
  • Visual issues such as blurry vision, problems with depth perception, trouble reading, or double vision
  • Finding you have the need to turn or tilt your head in order to see something clearly

Keep in mind that these symptoms do not have to be constant for you to have the condition.

Causes

While the cause of squint is not fully understood, this in many cases is known to involve a neuromuscular component with an abnormality. There are six muscles in the eye, and these must work together to successfully focus on a target. Problems that can interfere here and cause strabismus include:

  • Neurologic brain issues such as tumors, stroke, a neuromuscular condition such as myasthenia gravis that interferes with communication between nerves and muscles, or other health issues such as Graves’ disease resulting in too much thyroid hormone, or diabetes
  • Getting struck on the head or undergoing some other injury in the area
  • An injury or other issue involving the muscles themselves
  • Refractive errors that remain uncorrected (nearsightedness, farsightedness, astigmatism)
  • Conditions such as cerebral palsy, Down syndrome (where the condition can affect up to 60% of patients), or hydrocephalus (involving a buildup of fluid in the brain)
  • Nervous system issues

Diagnosis

To determine if you or your child (who is at least 4 months old) may have strabismus, it’s important to have a thorough eye examination. This should include the following:

  • A complete history considering any possible genetic connections, other health issues that may be contributing, or any medications or other substances that may play a role
  • Patient acuity, which can be assessed using a traditional Snellen letter chart to find how many letters can be read or with a very young child by observing behavior
  • Comparing refractive corrections by seeing how a series of different strength lenses can change vision
  • Testing for alignment and ability to focus
  • Dilating or widening the pupil using drops to assess what’s going on inside the eye

Treatment

There are a variety of approaches that can be used to tackle a squint issue. These include:

  • Getting glasses or contact lenses: If an issue with refraction—such as nearsightedness, farsightedness, or astigmatism—is at the root of the squint, then correcting this can help to solve the problem.
  • Performing eye exercises: These may help to strengthen the muscles to allow for better control of eye movements.
  • Patching the eye: If a patient also has lazy eye, treating this with a patch can improve vision and may have the added benefit of also improving eye alignment.
  • Getting eye muscle injections: This can temporarily help to weaken some eye muscles, thereby allowing them to better align.
  • Eye muscle surgery: Tightening or loosening eye muscles can improve the relative alignment of the eyes.

While it may be tempting to simply wait and see what happens with a squint, it’s important for a variety of reasons to seek treatment. Ignoring an emerging squint can lead to issues such as:

  • Amblyopia, otherwise known as a lazy eye, can develop when the brain begins to ignore signals from the eye that is misaligned and normal eyesight with depth perception does not develop.
  • Intermittent issues such as blurred or double vision can become persistent.
  • It can begin to have a real impact on self-esteem.

Prognosis

After undergoing treatment, it’s important to consult your doctor to see how successful this has been and determine if anything else needs to be done. The good news is that in young patients, if this is promptly treated, vision can develop entirely normally with perfect acuity.

When to Call a Doctor

Call a doctor immediately if you suddenly notice the appearance of squint, particularly in an older child or adult who may also have complaints of double vision. This may be an indicator of a more serious neurologic condition.

Summary

Squint (strabismus) is a condition in which one eye is focused in the correct direction while the other moves up or down or turns in or out instead. Several types of squint (strabismus) may occur at different ages with varying symptoms.

It has various causes, most of which involve the muscles and nerves that serve the eye. Squint can be diagnosed with an eye examination. Treatment will depend on the type of squint and may involve corrective lenses, eye exercises, eye patch, eye injections, or surgery.

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5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Moorfields Eye Hospital. Squint (strabismus).

  2. Cleveland Clinic. Strabismus (crossed eyes)? Updated January 22, 2019.

  3. Texas Children’s Hospital. Infantile esotropia.

  4. American Academy of Ophthalmology. What is adult strabismus?

  5. National Health Services. Overview squint. Updated January 6, 2020.