A turned eye in a child is not something to watch and wait on. Early treatment makes a real difference, and the results are often better than parents expect.
Strabismus is a condition in which the two eyes do not point in the same direction at the same time. One eye looks straight ahead while the other turns inward, outward, upward, or downward. It affects around 4 percent of children and can also develop in adults following neurological events, injury, or thyroid disease. In children, strabismus is closely linked to amblyopia and requires prompt treatment. In adults, it typically causes double vision and significant quality of life impact. Both groups have good treatment options.
What You Need to Know About Strabismus
- Strabismus means the eyes are misaligned: one eye turns in a different direction from the other
- It is not caused by weakness or laziness of the child. It is a neuromuscular coordination problem that is not the child’s fault
- Left untreated in children, strabismus causes the brain to suppress the turned eye, leading to amblyopia
- Some strabismus in children is caused by uncorrected long-sightedness and is corrected entirely by glasses
- Surgery is effective and often produces excellent alignment, but glasses and patching may still be needed afterward
- Adults who develop a sudden new squint require urgent assessment to exclude a neurological cause
Types of Strabismus
Esotropia
One eye turns inward toward the nose. The most common type in young children. Infantile esotropia appears in the first six months of life and requires surgery. Accommodative esotropia appears between ages 2 and 4 and is driven by uncorrected long-sightedness: the child’s efforts to focus for near vision cause the eyes to over-converge. Glasses that correct the long-sightedness can eliminate or greatly reduce the turn. A child who suddenly develops a convergent squint at age 2 to 3 should have a refraction done under cycloplegia as a first step before considering surgery.
Exotropia
One eye turns outward away from the nose. Often intermittent at first, noticed most when the child is tired, daydreaming, or looking into the distance. Many children with intermittent exotropia compensate well for years. Parents often notice one eye drifting outward in bright sunlight and the child squinting or closing that eye. Constant exotropia is less common than constant esotropia in children but becomes the more prevalent pattern in adults with longstanding strabismus.
Vertical strabismus
One eye turns upward (hypertropia) or downward (hypotropia) relative to the other. Can occur in isolation or alongside a horizontal deviation. Common causes include fourth nerve palsy, which causes the affected eye to tilt and the patient to adopt a characteristic head tilt to compensate, thyroid eye disease causing restrictive myopathy, and Brown syndrome, in which the superior oblique tendon restricts upward gaze in adduction. Vertical strabismus in adults with double vision requires careful workup to identify the cause before planning treatment.
Why Does Strabismus Develop?
In children
In most children, strabismus does not have a single identifiable cause. There is often a hereditary component: a parent or sibling with a squint raises the risk noticeably. Uncorrected refractive errors, particularly long-sightedness, are a major contributing factor for accommodative esotropia. Premature birth, developmental delay, and certain neurological conditions are associated with higher rates of strabismus. Rarely, a new squint in a child can be caused by a tumor or neurological lesion: a child who develops any new squint should be assessed promptly rather than observed.
In adults
A new squint in an adult with double vision has a different set of causes from childhood strabismus. Cranial nerve palsies (third, fourth, or sixth nerve) from microvascular ischaemia in patients with hypertension or diabetes are common. Thyroid eye disease causes restrictive myopathy that limits eye movement and produces vertical or horizontal double vision. Myasthenia gravis produces a variable strabismus that worsens with fatigue. Mechanical causes include orbital fractures and prior surgery. A new onset squint with diplopia in an adult always warrants neurological investigation.
Strabismus and Amblyopia
These two conditions are inseparable. When the eyes are misaligned, the brain receives two different images simultaneously. To avoid double vision, the brain suppresses the image from the turned eye. This suppression, sustained during the critical period of visual development in childhood, leads to amblyopia: the suppressed eye fails to develop normal visual acuity (VA) (VA testing), and that reduction in vision becomes permanent if not treated in time.
Treating strabismus without also treating the amblyopia it has caused is only half the job. Surgery aligns the eyes. Patching or atropine develops the vision in the amblyopic eye. Both are needed, and the younger the child when treatment starts, the better the outcome for both alignment and vision.
Treatment
Glasses
For accommodative esotropia, glasses correcting the underlying long-sightedness are the first step and sometimes the only treatment needed. The glasses need to be worn full-time, not just for near work, because the accommodative drive that causes the convergence operates at distance too. Parents sometimes resist full-time glasses in a two-year-old, but early compliance is critical. Some children’s accommodative esotropia fully resolves with glasses alone. Others achieve partial correction and need surgery for the residual deviation.
Patching and amblyopia treatment
Patching the dominant eye forces the brain to use the turned eye and develops its visual acuity. This is amblyopia treatment, not strabismus treatment: it improves the vision in the weaker eye but does not straighten it. It is done before surgery in children with significant amblyopia to maximise vision in both eyes, because a child with poor vision in the non-dominant eye makes a much better surgical candidate than one who is entirely dependent on a single eye.
Surgery
Strabismus surgery adjusts the tension on one or more of the muscles that move the eye, either weakening an overacting muscle or strengthening an underacting one. It is performed under general anaesthetic, typically as a day procedure. The eye is red and sore for a week or two afterward, which looks alarming but is normal. Most patients achieve good alignment from a single procedure; some need a second operation to fine-tune the result.
Botulinum toxin injection
Botulinum toxin injected into an overacting extraocular muscle temporarily weakens it, allowing the opposing muscle to bring the eye back toward alignment. The effect lasts two to four months and may produce lasting correction in some cases, particularly recent-onset strabismus from a cranial nerve palsy that may recover spontaneously. It is most useful as a temporary measure or as an alternative to surgery in selected patients.
Prism glasses
Prism lenses bend light before it enters the eye, compensating for the deviation and eliminating double vision in adults with strabismus. They do not treat the underlying deviation but provide symptomatic relief. Temporary stick-on Fresnel prisms are used to assess whether a prism will be helpful before incorporating permanent prism into spectacle lenses. Useful for small stable deviations, less practical for large deviations where the prism thickness becomes optic (see the fundus photography page)ally limiting.
What Surgery Can and Cannot Do
Many parents come in with mismatched expectations, so let’s be direct about what surgery does and doesn’t do. Strabismus surgery repositions the eyes. It does not fix the brain’s processing of vision from the turned eye. A child who has had surgery and is now cosmetically aligned still needs to be monitored for amblyopia and may still need patching afterward. Surgery is one step in the treatment, not the endpoint.
The cosmetic outcome matters genuinely. Strabismus affects how others perceive a child during formative social years, and correcting it carries real psychological benefit alongside the visual benefit. Perfect symmetry is not always achievable. Some under- or over-correction is common. A second procedure is not a failure of the first — it’s part of how strabismus is managed in a proportion of patients. Strabismus surgery is often iterative. That is completely normal and should be explained before the first operation, not discovered afterward.
For adults having surgery for longstanding strabismus, the situation is different. The amblyopia cannot be reversed in adulthood, and the realistic goal is cosmetic alignment and, where possible, the elimination of double vision. Many adults who had a squint as a child and are finally addressing it in their thirties or forties have outcomes they find significant in terms of confidence and social ease.
Seek Prompt Assessment If
- A child of any age develops a new squint, even if it seems to come and go
- An adult develops sudden new double vision or a visible eye turn that was not present before
- A child has a white pupil reflex in photographs instead of the normal red reflex
- A child with known strabismus seems to be developing a strong preference for one eye
A new squint in a child always needs assessment, not observation. In a small number of cases it is the presenting sign of a serious underlying condition including retinoblastoma, which is why any new squint with an abnormal red reflex is a same-day referral. A sudden new squint in an adult with diplopia needs neurological investigation urgently, as it can indicate a cranial nerve palsy from a structural cause.
Frequently Asked Questions About Strabismus
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Will my child grow out of their squint?
Pseudostrabismus — where wide nasal skin folds make the eyes appear crossed when they’re actually straight — does resolve as the face matures. Real strabismus does not. A child with a genuine eye turn will not grow out of it, and watching and waiting is not neutral: every month of untreated strabismus during the critical period of visual development carries a cost in terms of amblyopia risk. If you are unsure whether the squint is real, get it assessed. An orthoptist can make that determination quickly.
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Does wearing glasses really fix a squint?
For accommodative esotropia, yes, sometimes completely. The squint is driven by the effort of focusing through an uncorrected long-sighted prescription. Give the eye the right glasses, remove the need for that extra focusing effort, and the convergence reduces or disappears. This only works for the accommodative component of the squint. If there is a structural or non-accommodative component as well, surgery will still be needed for the residual deviation after the glasses have done their part.
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My child had surgery but the squint is coming back. Is this normal?
Regression after strabismus surgery is real and relatively common, particularly in the first few years. The eye muscles adapt over time and the deviation can drift back. This is not a sign the surgery failed. It’s how strabismus works in a proportion of cases. Many patients have two or more procedures over their lifetime and achieve excellent long-term alignment. Regular follow-up after surgery is needed precisely to catch regression early.
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I had a squint as a child that was never treated. Can anything be done now?
Yes, though the goals are different from treating it in childhood. The amblyopia from untreated childhood strabismus cannot be fully reversed in adulthood. But the alignment can be corrected surgically, the double vision can be addressed with prisms or surgery, and the cosmetic and psychological impact of having straight eyes for the first time is something many adults describe as genuinely life-changing. Age is not a barrier to strabismus surgery.
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Could my child’s squint be something serious?
The vast majority of childhood strabismus is benign and related to refractive error or idiopathic muscle imbalance. A small proportion is associated with more significant conditions: retinoblastoma can present as a squint, as can intracranial tumours or other neurological causes. This is why any new squint in a child should be assessed promptly rather than observed. The examination takes minutes and provides reassurance in most cases. The cases where something serious is found are exactly why prompt assessment matters — and equally, why most parents leave the clinic reassured.
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Will my child need glasses after surgery?
If they needed glasses before surgery for a refractive error, they will almost certainly still need them afterward. Surgery moves the eyes to a new position; it does not change the optics of the eye. A child with accommodative esotropia who had surgery for a residual deviation after glasses still needs those glasses to maintain the alignment the surgery achieved. Taking the glasses off after surgery to see if the eyes stay straight is usually a bad idea and often leads to the squint returning.
If you would like to learn more, the American Optometric Association’s strabismus page and the NCBI StatPearls review on strabismus offer additional information about the condition, its evaluation, and treatment.
Strabismus (ocular misalignment) is a failure of the binocular vision system to maintain simultaneous bifoveal fixation. The eyes point in different directions, with the deviating eye positioned nasally (esotropia), temporally (exotropia), superiorly (hypertropia), or inferiorly (hypotropia) relative to the fixating eye. Strabismus affects approximately 3-4% of the population and is the most common cause of amblyopia in children. The clinical importance extends beyond cosmesis: constant unilateral strabismus suppresses the deviating eye’s cortical input during the critical period, causing amblyopia; binocular strabismus without amblyopia still deprives the patient of stereoacuity and binocular summation. In adults, acquired strabismus from cranial nerve palsy, thyroid eye disease, or orbital pathology causes disabling diplopia that requires prompt diagnosis and targeted management. The choice between non-surgical (optical, prism, orthoptic) and surgical treatment depends on the type, onset, and size of the deviation, and on the binocular vision status.
Clinical Overview: Strabismus
- Classification: Esotropia (ET): eye turns in , accommodative (hyperopia-driven, AC/A ratio), non-accommodative (infantile, acquired non-accommodative), restrictive (TED), paretic (VI nerve palsy). Exotropia (XT): eye turns out , intermittent (most common XT in children, often distance-predominant), constant, consecutive (post-surgical ET). Vertical: hypertropia/hypotropia , IV nerve palsy (most common paretic cause), Brown syndrome, double elevator palsy.
- Cover test: Unilateral cover test (cover/uncover) detects a manifest tropia , the uncovered eye moves to take up fixation when the fixing eye is covered. Alternating cover test (alternate occlusion) detects the total deviation (phoria + tropia). Prism cover test quantifies the deviation in prism diopters (PD). Always perform in primary gaze, upgaze, downgaze, and near and distance fixation.
- Accommodative esotropia: Hyperopia causes increased accommodation to see clearly, with consensual convergence exceeding the divergence fusional amplitude. Management: full cycloplegic hyperopic correction. If the esotropia resolves fully with spectacles: pure accommodative ET , no surgery. If a residual angle remains: non-accommodative component requiring surgical correction of the residual angle. Do not under-plus the prescription.
- Intermittent exotropia (IXT): Most common XT in children. Exodeviation that is manifest in distance fixation or when the child is tired or daydreaming, but controlled (held as a phoria) at near. Newcastle Control Score or Office Control Score quantifies control. Watchful waiting is appropriate for well-controlled IXT; surgery indicated when control deteriorates, angle increases, or binocular vision deteriorates.
- Surgery: Recession (weakening , moves the muscle insertion posteriorly), resection (strengthening , shortens the muscle and reattaches anteriorly), adjustable sutures (post-operative adjustment under topical anaesthetic when the patient is cooperative). Effect varies by muscle and muscle length. Aim for slight overcorrection immediately post-op (residual small-angle ET in XT surgery; small-angle ET/exo in ET surgery) as the eye tends to drift toward the pre-operative position.
- Botulinum toxin: Injection into the antagonist muscle weakens it temporarily (3-4 months effect), allowing the paretic muscle to recover in cranial nerve palsy. Also used for small-angle acquired ET, consecutive ET, and in children as an alternative to early surgery for infantile esotropia.
Pathophysiology
Binocular single vision (BSV) requires simultaneous bifoveal fixation with fusion , the combining of the two slightly disparate retinal images into a single percept. This depends on accurate ocular alignment, which is maintained by tonic vergence, fusional vergence reflexes, and the motor control of the extraocular muscles (EOMs). When alignment breaks down, two responses are possible: diplopia (older children and adults, whose visual cortex has already established binocular connections) or suppression (younger children in the critical period, who suppress the deviating eye’s image to avoid confusion and rivalry).
Infantile esotropia: Onset before 6 months of age. Large-angle constant ET (typically 30-50 PD). The cortex lacks mature binocular connections at this age , there is no fusion to break down, only suppression developing. High rates of associated nystagmus, dissociated vertical deviation (DVD), and amblyopia. Surgery is required because spectacles cannot correct a non-accommodative ET. Timing of surgery: alignment by age 2 years is associated with better binocular outcome than later surgery.
AC/A ratio and accommodative ET: The accommodative convergence to accommodation (AC/A) ratio describes the amount of convergence produced per diopter of accommodation. A high AC/A ratio means excessive convergence for a given amount of accommodation , driving esotropia. Bifocal lenses (for high AC/A esotropia) reduce the near accommodative effort and the convergence it drives, reducing or eliminating the near ET without surgery. A normal AC/A ratio with esotropia that resolves fully with distance correction = pure accommodative ET; bifocals not needed.
Assessment
Ocular motility: Examine pursuit, saccades, and ductions (see visual field context) (uniocular movements) in the nine diagnostic positions of gaze. Identify any limitation. Pattern strabismus: A-pattern ET worsens in downgaze (overaction of superior oblique); V-pattern ET worsens in upgaze (overaction of inferior oblique). Oblique muscle dysfunction is common in infantile strabismus and affects surgical planning.
Binocular vision assessment: Worth 4-dot test (at distance and near): suppression vs fusion vs diplopia. Visual acuity and Randot/Titmus stereotest: quantifies stereoacuity (from 40 arc seconds in normal to 3000 arc seconds in gross stereopsis; absent in dense suppression). Bagolini striated glasses: assesses peripheral fusion and suppression scotoma. Lang stereotest: suitable for preverbal children (uses random dot stereograms that require no special glasses). The binocular vision profile informs the prognosis for restoring single binocular vision and the urgency of intervention.
Management
Spectacle correction first: Full cycloplegic refraction and spectacle correction in all children with strabismus, before any surgical decision. Accommodative ET: prescribe full hyperopic correction; reassess at 6-8 weeks. If ET resolves fully: non-surgical management with annual review. If residual angle: plan surgery on the residual non-accommodative angle only (not the full presenting angle). Spectacles must be worn during examination before and after any surgery for accurate angle measurement.
Amblyopia treatment: Treat amblyopia before strabismus surgery whenever possible. Improving VA in the amblyopic eye maximizes the sensory drive for fusion after alignment, improving surgical outcomes. The exception: infantile ET with equal VA , align early for best binocular outcome without waiting.
Strabismus surgery principles: Recession weakens a muscle (pushes the insertion further from the limbus). Resection strengthens a muscle (shortens it before reattachment). Adjustable sutures: the muscle is tied with a slip knot under GA; adjustment of the suture tension is performed the next day under topical anaesthetic while the patient is cooperative , allows fine-tuning of alignment. Most useful in adults with acquired strabismus where the expected dose-response is less predictable.
Acquired strabismus in adults: Diplopia from IV nerve palsy (vertical, torsional), VI nerve palsy (horizontal ET), III nerve palsy (exotropia, ptosis, mydriasis), thyroid eye disease (restrictive HT or ET), or post-trauma. Management: prism glasses for stable small-angle deviations; botulinum toxin while awaiting spontaneous recovery; strabismus surgery once the deviation has been stable for 6 months. Always exclude structural cause before labeling a nerve palsy as “microvascular” in patients over 50 , imaging is required if there are atypical features (pain, pupil involvement in III palsy, other cranial nerve signs).
Surgical Planning and Outcomes
Surgical dosage: Based on the largest stable angle under best optical correction, measured under controlled conditions (prism cover test in primary gaze at distance and near, with appropriate spectacle correction in place). Avoid operating on an angle measured on the day of first presentation , it may not represent the stable deviation. For intermittent XT: measure the largest angle over multiple visits. Surgical rules of thumb: approximately 5-6 PD of correction per mm of recession of a horizontal rectus muscle (varies with muscle and starting insertion point).
Binocular outcome vs cosmetic outcome: Adults and older children with longstanding constant strabismus have established suppression and will not regain stereoacuity after surgery. Surgery provides cosmetic alignment and may restore peripheral fusion, but central stereoacuity is not recoverable after years of suppression. This must be communicated clearly , patients who expect to “see normally with both eyes together” after adult cosmetic strabismus surgery may be disappointed. In children operated early, genuine binocular potential can be restored if amblyopia is treated and alignment is achieved within the critical period.
Clinical Decision Points
- Infantile ET, age 9 months, 40 PD, full spectacle correction in place, no reduction in ET: Non-accommodative component. Operate by 18-24 months for best binocular outcome. First treat any amblyopia.
- Accommodative ET resolves at distance but 15 PD residual at near: High AC/A ratio. Add bifocals (+2.50 D or +3.00 D addition) to the existing spectacles. Reassess at 3 months. If near ET resolves: continue bifocals. If not: surgery on residual near angle with preservation of spectacle correction.
- Intermittent XT, age 5, Newcastle control score worsening: Reassess every 3-4 months. If control deteriorates over two consecutive visits or the angle exceeds 20-25 PD at distance: offer surgery.
- Adult with new diplopia, esotropia, no trauma: Check for VI nerve palsy (limitation of abduction). MRI brain if any atypical features. If microvascular VI palsy presumed: 3-month observation for spontaneous recovery. Prism glasses for interim diplopia management. Botulinum toxin to the ipsilateral medial rectus if significant deviation and no recovery at 6 weeks.
- Third nerve palsy, partial, with pupil involvement: Do not wait for spontaneous recovery , image immediately to exclude posterior communicating artery aneurysm. Pupil-involving III nerve palsy is an aneurysm until proven otherwise.
Same-Day Assessment Required
- New diplopia with pupil-involving third nerve palsy , posterior communicating artery aneurysm until proven otherwise; emergency CTA or MRA
- New-onset diplopia with other cranial nerve signs or headache , intracranial pathology; emergency neuroimaging
- Sudden large-angle strabismus with restricted motility in a known thyroid eye disease patient , DON emergency (see TED page)
A partial or complete third nerve palsy with pupillary mydriasis is an aneurysm of the posterior communicating artery until imaging proves otherwise. The pupillary fibers of the third nerve travel on the outer surface of the nerve and are compressed by an expanding aneurysm before the motor fibers. Diabetic and other microvascular third nerve palsies typically spare the pupil because the ischemia affects the inner (motor) fibers. This distinction has life-saving implications: a pupil-involving III palsy must be imaged as an emergency, not observed for spontaneous resolution.
Clinical Pearls: Strabismus
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Spectacles must be worn during strabismus surgery planning. Measuring angle without full optical correction produces the wrong target angle.
In accommodative or partially accommodative esotropia, the deviation measured without spectacles includes both the accommodative component (which spectacles will remove) and the non-accommodative component (which surgery addresses). Operating on the total bare angle , without spectacles , will produce an overcorrection, leaving the child exotropic after surgery once they put their glasses back on. The surgical target is always the residual angle measured with the full spectacle correction in place, over multiple visits, at an age when the correction is stable. This error , operating on the wrong angle , is one of the most common and preventable causes of strabismus surgical failure.
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Intermittent exotropia is not urgent surgery. Control, not angle size, drives the timing decision.
The reflex to “fix” a noticeable exodeviation in a child by scheduling early surgery fails to account for the natural history of intermittent XT. Many children with IXT maintain good binocular control at near, have normal stereoacuity when the tropia is not manifest, and improve spontaneously during childhood. The Newcastle Control Score and the Office Control Score quantify how often and how easily the deviation is controlled , these are better predictors of the need for surgery than the angle size alone. Early surgery for a well-controlled IXT is not indicated and carries the risk of consecutive esotropia. Surgery when control deteriorates, when the deviation is becoming constant, or when stereoacuity is definitively declining is the correct approach.
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The cosmetic result of strabismus surgery is not the same as the binocular result. Counsel patients and families accurately.
Parents of a child with longstanding strabismus often understand surgery as making the eyes “work together.” For children operated early with good amblyopia treatment, this may be true , binocular potential is restored with good alignment. For adults or older children with longstanding constant strabismus, suppression is deeply established and stereoacuity is not recoverable. Surgery restores the appearance of alignment and may improve peripheral fusion, but central binocular single vision is not achieved. Setting this expectation before surgery , and documenting it , avoids the common situation of a cosmetically successful operation being perceived by the patient as a failure because diplopia appeared or “proper” binocular vision was not restored.
Further reading: RCOphth Paediatric Ophthalmology Guidelines. Related conditions: amblyopia (most common sequela of strabismus), thyroid eye disease (restrictive strabismus in adults). Subspecialty context: pediatric ophthalmology subspecialty page.