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Squint Causes in Children and Adults: Why Does an Eye Turn?
Squint causes depend on age. In children, a squint is often the eye straining to overcome a focusing problem such as long-sightedness, with family history, premature birth and brain or nerve conditions adding risk; sometimes no cause is found. In adults it is usually a muscle or nerve problem, such as diabetes, thyroid eye disease, stroke or head injury. Any new squint needs an eye examination. Prof. Dr. Ahmet Satıcı treats squint at Laser Istanbul Clinic.
What are the main squint causes?
A squint, medically called strabismus, happens when the two eyes stop pointing at the same target because something disturbs the muscles that move the eye, the nerves that control them, or the brain's control of eye movement. The NHS describes a squint as eyes that point in different directions: one eye may turn in, out, up or down while the other looks straight ahead, either all the time or only sometimes.
The American Association for Pediatric Ophthalmology and Strabismus (AAPOS) says most strabismus results from an abnormality of the neuromuscular control of eye movement, including the brain's part in it. That is why the causes of squint look so different from each other: a focusing error, a tendency that runs in a family, a muscle affected by thyroid disease and a nerve affected by a stroke all end in the same visible sign. AAPOS estimates that about 4% of the US population has strabismus, and the Royal College of Ophthalmologists (RCOphth) puts childhood strabismus at 2.1% of UK children.
The main squint causes at a glance:
| Group | Examples | Mostly seen in |
|---|---|---|
| Focusing (refractive) problems | Long-sightedness (hypermetropia), short-sightedness, astigmatism, a marked difference between the two eyes | Children |
| Inherited tendency | Squint or lazy eye in a parent, brother or sister | Children and adults |
| Birth and pregnancy factors | Premature birth, low birth weight, assisted delivery, maternal smoking in pregnancy | Children |
| Brain and nerve conditions | Cerebral palsy, Down's syndrome, hydrocephalus, developmental delay, brain tumour, stroke | Children and adults |
| Poor vision in one eye | Cataract, scarring, retinal or optic-nerve disease, injury | Children and adults |
| Nerve or muscle disease | Diabetes, thyroid eye disease, myasthenia gravis, head injury | Mainly adults |
| Earlier eye surgery | Damage to an eye muscle, or an over-correction after squint surgery | Adults and children |
| Unknown | No cause found | Often infants and young children |
What are the squint eye causes in a child?
In children, a squint is most often linked to a focusing problem, an inherited tendency or a birth-related risk factor, and in many children no single cause is identified. The NHS says squints in children are often caused by the eye attempting to overcome a vision problem, such as short-sightedness, long-sightedness or astigmatism, and adds that the exact cause is not always known. The RCOphth guideline notes that childhood strabismus generally begins before the age of 5 and that most affected children are otherwise healthy.
Long-sightedness (hypermetropia) and other focusing problems
A long-sighted child has to focus harder than normal. Because focusing and eye-turning are linked, that extra effort can pull one eye inwards, which is called accommodative esotropia. The RCOphth describes it as an inward squint caused by uncorrected hypermetropia (usually more than +2.0 dioptres), usually starting between 2 and 5 years of age and often seen when a child is tired or concentrating on close objects. It makes up 36.4% of childhood esotropia in the guideline, and glasses that fully correct the long-sightedness can straighten the eyes. The guideline also states that hypermetropia and anisometropia (a clear difference in prescription between the two eyes) greatly increase the risk of developing amblyopia (lazy eye) and strabismus.
Does a squint run in families?
Yes, a squint can run in families, though it is not certain to be passed on. The NHS says squints sometimes run in families, and AAPOS says strabismus can run in families. The RCOphth lists a family history of strabismus or amblyopia among the conditions associated with squint and recommends a higher level of surveillance for such children. EyeWiki, the American Academy of Ophthalmology's (AAO) clinical encyclopedia, lists a positive family history among the risk factors for esotropia. If a parent had a squint or lazy eye, an eye check in the early years is sensible.
Premature birth, low weight and pregnancy factors
The RCOphth reports that squint is more common after assisted delivery (forceps or caesarean section), in children with low birth weight, including premature babies, and in children with neuro-developmental disorders. It adds that squint linked to a neuro-developmental problem is independently associated with maternal smoking later in pregnancy, maternal illness in pregnancy and low birth weight for gestational age. EyeWiki also lists prematurity, low birth weight and maternal smoking in pregnancy among the risk factors for esotropia, and prematurity and maternal alcohol or substance use for exotropia. These are risk factors, not blame: most children with these factors do not develop a squint, and many children with a squint have none of them.
Brain, nerve and genetic conditions
The NHS lists rarer causes: measles, Down's syndrome, developmental delay, cerebral palsy and other brain or nerve problems. AAPOS adds hydrocephalus (a build-up of fluid around the brain) and brain tumours to the conditions that go with strabismus in children, and the RCOphth also lists craniofacial syndromes and fetal alcohol syndrome. Squint in these children is part of a wider picture, and their care is usually shared with a paediatrician.
Squints with no known cause
Some squints appear without any of the above. Infantile esotropia, an inward turn that starts in the first 6 months of life, is described by the RCOphth as idiopathic, meaning no cause is known; the guideline quotes estimates up to 1 in 400 live births. Intermittent exotropia, an outward turn that comes and goes, affects up to 1% of children, usually starts at 2–4 years and also has no known underlying cause. The RCOphth notes that parents see it when a child is tired, daydreaming or in bright sunlight, and AAPOS adds that it can show when a child is ill or bored.
| Squint type | Typical start | Known driver | Source |
|---|---|---|---|
| Infantile esotropia (inward) | Before 6 months | None known; family history and prematurity are risk factors | RCOphth, EyeWiki |
| Accommodative esotropia (inward) | 2–5 years | Uncorrected long-sightedness | RCOphth |
| Intermittent exotropia (outward) | 2–4 years | None known | RCOphth, AAPOS |
| Sensory squint (inward or outward) | Any age | Poor vision in one eye | AAPOS, EyeWiki |
What causes sudden eye turning in a child?
A squint that appears suddenly in a child needs a prompt eye examination, because most childhood squints start gradually and a sudden one can occasionally signal a serious problem. The RCOphth lists "sudden onset strabismus" among the possible indications for neuro-imaging, together with headaches, cranial nerve palsies, an abnormal pupil response, optic nerve disease and unexplained loss of vision. It also says that behaviour change or headache in a child with a squint should be considered suspicious of serious neurological disease.
Possible explanations a doctor will look for:
- A cranial nerve palsy. The RCOphth says a cranial nerve palsy must be considered at all times, particularly when the eye movements are limited.
- An acquired inward squint with acute onset. The RCOphth notes that the onset of acquired non-accommodative esotropia may be acute, and a doctor needs to check that it is not caused by a nerve or neurological problem.
- Poor vision in one eye. If one eye sees badly for any reason, it may drift. The NHS lists retinoblastoma, a rare childhood eye cancer, among causes of squint, and the RCOphth says a squint can be the first sign of a serious eye or brain condition such as retinoblastoma, hydrocephalus or a brain tumour.
- An intermittent squint that has become easier to see, for example during illness or tiredness. This is usually harmless but still needs assessing.
What to do: the NHS advises seeing a doctor if a child has a squint all the time, or one that comes and goes after the age of 3 months. AAPOS says constant eye crossing at any age is worrisome and that any crossing beyond 4 months of age should be checked. Take a recent photograph showing the turn and note when it happens. If there is also headache or a change in behaviour, contact a doctor promptly. Surgery is never the first step: the cause comes first.
What are the squint eye causes in adults?
In adults, a squint either dates from childhood or is new, and a new squint is often caused by a nerve or muscle problem that needs its own medical assessment. The AAO says many adults have had strabismus since childhood, while others develop it later. The causes it and AAPOS list for adults include:
- Diabetes. The AAO names diabetes among the health conditions that can lead to strabismus.
- Thyroid eye disease. EyeWiki explains that the eye muscles become inflamed and enlarged, which stops the eye moving normally; the inferior rectus (the muscle that pulls the eye down) is the one most often affected.
- Myasthenia gravis. The AAO lists this muscle-weakness condition as a cause.
- Stroke, brain tumour or other brain problems. AAPOS lists stroke or vascular problems, and neurological problems, and the AAO adds brain tumours.
- Head injury. AAPOS and the AAO both list trauma, whether to the brain, the nerves or the muscles themselves.
- Earlier eye surgery. The AAO notes that eye surgery can damage the eye muscles. After squint surgery for an inward turn, EyeWiki says an outward turn (consecutive exotropia) can appear, in most cases from a surgical overcorrection.
- A childhood squint that was never treated. The AAO says many adults have had strabismus since childhood.
- Poor vision in one eye. EyeWiki describes sensory exotropia as a blind or poorly seeing eye drifting outwards, which typically happens in children older than 2–4 years and in adults. A cataract or other cause of lost vision in one eye can therefore bring on a squint.
Why double vision matters. The AAO lists double vision among the symptoms of adults who develop strabismus after childhood. The NHS says to get advice if a squint or double vision develops in adulthood, and to call 111 or arrange an urgent GP appointment for double vision that started suddenly or double vision with eye pain. It lists severe headache or an enlarged pupil with blurred or double vision, and double vision after a head injury, as reasons to call 999 or go to A&E. Outside the UK, use your local emergency number.
What are the squint eye symptoms?
Squint eye symptoms are a visible turn of one eye, often with signs that the person is trying to compensate. The NHS lists an eye that turns in, out, up or down, a squint that is constant or comes and goes, and a child who turns the head or keeps one eye closed when looking at things.
| Children | Adults | |
|---|---|---|
| Visible sign | One eye looks in a different direction, all the time or only at times | The same, or a subtle change after illness or injury |
| What the person notices | Often little; many children do not complain | Double vision, blurred vision, eye strain, difficulty reading, loss of depth perception (AAO) |
| Compensating habits | Head turn, or closing one eye (NHS) | Head tilt to see clearly (AAO) |
| Hidden risk | A lazy eye (amblyopia), where vision in the turned eye does not develop | Daily tasks such as reading become harder |
The NHS warns that an untreated squint can lead to blurred or double vision, a lazy eye and embarrassment or low self-esteem. EyeWiki notes that about half of children with esotropia develop amblyopia, which is why finding the cause early matters.
How do doctors find the cause of a squint?
Finding the cause starts with a full eye examination, because the cause decides the treatment. In children, the RCOphth guideline describes a history that covers birth, prematurity, developmental milestones and family history, followed by measurement of vision, the alignment of the eyes with and without glasses (cover tests) and a prescription check with the right correction for any long-sightedness. If the squint is new or eye movements are limited, the examiner considers a cranial nerve palsy; any abnormal neurological sign prompts referral to a paediatrician and consideration of an MRI or CT scan.
At Laser Istanbul Clinic, Prof. Dr. Ahmet Satıcı examines the eyes, measures the squint, the eye movements and the focusing of each eye, and checks how the eyes work together before advising on treatment. If your reports point to another eye problem behind the squint, Doç. Dr. Muhammet Derda Özer (Doç. means Associate Professor), our retina and ocular oncology specialist, can review reports and scans for a second opinion. You can send your reports through our online consultation first.
Which squint causes can be treated, and how?
Treatment follows the cause: glasses for focusing causes, lazy eye treatment for poor vision, medical care for an underlying illness, and eye-muscle surgery for the turn that remains. The NHS lists glasses, eye exercises, surgery and muscle injections (whose effect lasts less than 3 months) as the main options, and says surgery is for when other treatments are not suitable or do not help.
| Cause | First step | Where surgery fits |
|---|---|---|
| Long-sightedness and other prescription problems | Full glasses correction | Only for a turn that remains with glasses on |
| Lazy eye (amblyopia) | Glasses, patching or blurring drops, ideally before age 7 (NHS) | After vision treatment, if the eyes are still misaligned |
| Infantile esotropia | Examination and treatment of any lazy eye | EyeWiki reports that early surgery (before age 2) gives more potential for the two eyes to work together |
| Intermittent exotropia | Monitoring | When the turn shows often or causes eye strain or double vision (AAPOS) |
| Nerve palsy, thyroid eye disease, myasthenia, stroke | Investigate and treat the underlying condition first | Considered afterwards, if a turn remains |
| Poor vision in one eye (for example a cataract) | Treat the cause where possible | May still be considered for the alignment |
| Squint since childhood, in an adult | Assessment of alignment and double vision | Can be done at any age; AAPOS says eyes can be straightened even in people in their 90s |
Prof. Dr. Ahmet Satıcı performs squint surgery for adults and children and recommends it only when glasses and other treatments are not enough. The technique, recovery and what is included are explained on our treatment page.
Frequently asked questions
A squint is caused by a problem with the eye muscles, the nerves that control them or the brain's control of eye movement. In children it is often linked to focusing problems such as long-sightedness, to a family history or to premature birth. In adults the causes include diabetes, thyroid eye disease, stroke and head injury. In many young children no cause is found.
The most frequent are uncorrected long-sightedness or another prescription problem, a family history of squint, prematurity or low birth weight, and neurological conditions such as cerebral palsy or Down's syndrome. Rarely, a squint is the first sign of a serious eye or brain condition, which is why every new squint should be examined.
It can run in families: the NHS and AAPOS both say so, and a family history of squint or lazy eye is a recognised risk factor. Having a parent with a squint does not mean a child will certainly develop one, but an early eye check is a good idea.
A sudden squint can come from a nerve palsy, from an acquired inward squint with acute onset, or, rarely, from a serious eye or brain condition. The RCOphth lists sudden onset strabismus as a possible indication for neuro-imaging. Book an eye examination promptly, and contact a doctor straight away if there is also headache or a change in behaviour.
The AAO names diabetes, thyroid eye disease, myasthenia gravis, brain tumours, stroke, head injury and earlier eye surgery. A childhood squint that was never treated, or poor vision in one eye, can also be responsible. New double vision in an adult needs prompt assessment.
None of the sources we reviewed lists screen use or ordinary eye strain as a cause of squint. Tiredness can make an existing intermittent squint easier to see, as the RCOphth notes for intermittent exotropia, but the underlying cause is something else. If your or your child's eyes drift when tired, have them examined.
No. Squinting means narrowing your eyes to see better, and the US National Eye Institute lists it as a symptom of short-sightedness. A squint (strabismus) is when the eyes do not point the same way. If a child squints to see, an eye test for glasses comes first; if one eye drifts, see an eye specialist.
Yes. AAPOS says eyes can be straightened at any age, and the NHS says surgery can improve alignment even when a squint has gone untreated for a long time. The cause still has to be understood first, especially when the squint is new.
Worried about a squint in you or your child?
Prof. Dr. Ahmet Satıcı at Laser Istanbul Clinic assesses squint in adults and children, looks for the cause before recommending anything, and explains your options in writing. Surgery takes place in a fully equipped, Ministry of Health–licensed operating theatre in Istanbul.
Sources for the facts on this page
- External pages opened and checked on 7 Oct 2026.
- NHS. Squint. https://www.nhs.uk/conditions/squint/
- NHS. Lazy eye. https://www.nhs.uk/conditions/lazy-eye/
- NHS. Double vision. https://www.nhs.uk/symptoms/double-vision/
- The Royal College of Ophthalmologists. Guidelines for the Management of Strabismus in Childhood (March 2012). https://www.rcophth.ac.uk/wp-content/uploads/2026/06/Management-of-strabismus-guideline.pdf (listed at https://www.rcophth.ac.uk/guidance-resources/management-of-strabismus-in-childhood/)
- American Association for Pediatric Ophthalmology and Strabismus (AAPOS). Strabismus. https://aapos.org/glossary/strabismus
- AAPOS. Esotropia. https://aapos.org/glossary/esotropia
- AAPOS. Exotropia. https://aapos.org/glossary/exotropia
- American Academy of Ophthalmology. Adult Strabismus. https://www.aao.org/eye-health/diseases/what-is-strabismus
- EyeWiki (AAO). Esotropia. https://eyewiki.org/Esotropia
- EyeWiki (AAO). Exotropia. https://eyewiki.org/Exotropia
- EyeWiki (AAO). Infantile Esotropia. https://eyewiki.org/Infantile_Esotropia
- EyeWiki (AAO). Thyroid Eye Disease. https://eyewiki.org/Thyroid_Eye_Disease
- National Eye Institute (NIH). Nearsightedness (Myopia). https://www.nei.nih.gov/eye-health-information/eye-conditions-and-diseases/nearsightedness-myopia
- Facts carried over from the treatment page and doctor profile (already sourced there): early surgery before age 2 for infantile esotropia (EyeWiki); eyes can be straightened at any age (AAPOS); surgery can help even after long delay (NHS); clinic facts (squint on Prof. Dr. Satıcı's treatment list; Doç. Dr. Özer's retina and ocular oncology fields): content/en/strabismus.md, content/en/doctor-1.md.