Strabismus (heterotropia or tropia) is a misalignment of the visual axes which prevents bifoveal fixation. This results in disruption of binocularity with loss of fusion and stereopsis. In childhood, strabismus is associated with sensory adaptations such as suppression and amblyopia. Past neurophysiologic animal studies have demonstrated that this interruption to binocular vision in the critical period of vision development results in a marked reduction of binocularly driven cells in the visual cortex that limits the potential for stereopsis.1

Strabismus may be primary with no other ophthalmic or systemic problems, or secondary due to an associated ocular or systemic disorder. Frequently there is a genetic predisposition to strabismus.

Ocular conditions causing a sensory strabismus include developmental abnormalities of the eyes, cataracts, intraocular infection or inflammation, and tumours such as retinoblastoma. Systemic associations include developmental delay, prematurity, muscular diseases, or neurological conditions such as cerebral palsy, or intracranial tumours. This discussion will review only primary strabismus in children as secondary causes were reviewed previously in mivision by Dr Craig Donaldson (February 2025) and Dr Sandra Staffieri (September 2025).

There are two distinct ways to reduce the magnitude of strabismus. Firstly, using glasses to manipulate the accommodative/ convergence relationship (i.e. plus lenses for esotropia and minus lenses for exotropia). Secondly, by way of physically changing the balance of forces between the extraocular muscles, as with strabismus surgery or with chemodenervation (injecting botulinum toxin directly into the muscle). Occlusion therapy (patching) of the fixing eye to improve vision in the amblyopic eye, or convergence or fusion exercises for intermittent exotropia, may help to improve control of the turn and hence the frequency of the deviation.

Realignment of the eyes will restore binocular single vision (BSV), thus eliminating the cause of amblyopia, and importantly, improve cosmesis. It has long been noted that significant psychosocial issues have been associated with an uncosmetic tropia, including low self-esteem and lack of self-confidence, which can impact socialisation, quality of life, and employment opportunities.2-9There are reports of significant improvement in the psychosocial wellbeing of individuals following strabismus surgery, the importance of which should not be underestimated.6,10-12

OCULOMOTOR IMMATURITY

Babies often have a misalignment of their eyes in the first few months of life, most commonly a divergence of the eyes.13 This may just reflect an immaturity of the oculomotor system at that young age. As a general guideline, babies should be fixing well by six weeks and the eyes should be straight from three months of age. I often say to the parents that the baby has to learn to coordinate their eye movements, similar to how they have to learn to control the muscles of their legs before they can walk. Hence there is not a high index of suspicion with regard to strabismus in the first few months of life. Checking for a normal red reflex in each eye can be reassuring at this stage. If, however, the parents are still noticing a turn by three to four months of age, an ophthalmic assessment should be sought for dilation, cycloplegic refraction, and fundoscopy.

PSEUDOSQUINT (PSEUDOSTRABISMUS)

Sometimes, after the first few months of life, parents may still think their child has a turn in their eyes. This is because of the shape of the child’s face with a flat, broad nasal bridge and vertical skin folds nasally (epicanthus). This gives the optical illusion of a squint, particularly if the child looks in side-gaze. However, the corneal light reflexes remain symmetrical, and there is no tropia movement on cover testing, confirming pseudostrabismus and not a real turn.

STRABISMUS IN AUSTRALIA

Historically, a large population-based Australian study of predominantly six-year-old children (n=1,739) found the prevalence of strabismus to be 2.8%.14 Esotropia (ET) was the most common form of strabismus and often associated with significant hypermetropia, defined as ≥+3.00 DS. As expected, the prevalence of amblyopia was much higher in children with strabismus than non-strabismic children.

More recently, with the rapid rise in prevalence of childhood onset myopia,15,16 intermittent exotropia has become an increasingly common pattern of strabismus in Australia.

Infantile Esotropia

Infantile esotropia is defined as a large angle esotropia present by six months of age. Typically, the angle of the turn is greater than 30 prism dioptres (PD), but it is often over 50 PD. Infantile esotropia is primarily a surgical consideration and exercises / vision therapy will not change the angle of the turn. Early surgery, generally defined as occurring before two years of age,17-21 with adequate surgical alignment is associated with “improved stereoacuity outcomes, lower rates of subsequent misalignment, and reduced risk of moderate to severe amblyopia”.22 High grades of stereopsis have occasionally been reported in some children aligned before six months of age.23-25 Generally, however, stereopsis remains uncommon following surgery for infantile esotropia. In Birch and Stager’s study, 38% of children had some demonstrable stereoacuity when surgery was performed before six months of age, but only 4% had high-grade stereoacuity of 60 seconds of arc or better.25 Birch et al. confirmed that it was the duration of misalignment, rather than the actual age of the child at the time of surgery, that was the most important factor with regard to stereoacuity outcomes.20 Another benefit of early surgery is the significant improvement of both cognitive and psychomotor development in children postoperatively.22,26-28

Figure 1. A patient with pseudostrabismus: marked epicanthal folds but light reflexes central and symmetrical and no tropia on cover testing.

Figure 2. Infantile esotropia with large alternating esotropia.

Secondary associations of infantile esotropia often develop with time, including latent nystagmus (nystagmus induced when one eye is covered), dissociated vertical deviation (DVD), and inferior oblique overaction. Latent nystagmus and DVD are particularly indicative of a disruption of binocular vision occurring early in life.

Further squint surgery for infantile esotropia may be required to correct any residual esotropia, or a consecutive exotropia, which can occur following the initial surgery – even some years later. Surgery may also be required for the associated vertical deviations of inferior oblique overaction and DVD.

Accommodative Esotropia

This pattern of strabismus historically is the most common form of childhood esotropia, at least in Western populations,14,29,30 and typically presents from around 18 months to three years of age. It is well established that the risk of developing esotropia rises significantly with increasing levels of hypermetropia, particularly over +3.00 DS.31,32

The aim of treatment is to restore BSV and thereby eliminate the potential onset of amblyopia. This is achieved by initially giving the full hypermetropic correction. In doing so, a child with a fully accommodative esotropia will become orthotropic (binocular) again. Cycloplegic refraction (with a true cycloplegic agent such as cyclopentolate, rather than a mydriatic such as tropicamide) is mandatory to uncover all the latent as well as manifest hypermetropia. Undercorrecting the hypermetropia, as an initial step to allow the child to ‘get used to the glasses’, may convert a fully accommodative esotropia into a partial accommodative esotropia.33 The longer the delay, the more likely the outcome of a partial accommodative esotropia with the subsequent ongoing concerns of suppression, amblyopia, and loss of stereopsis.34

Figure 3. Accommodative esotropia. The eyes are straight (orthotropic) with full correction of hypermetropia.

Similar to infantile esotropia, it is the duration of misalignment that is most critical for a good stereopsis outcome in children with accommodative esotropia, as children with longer periods of misalignment had reduced or poor stereoacuity.35,36 In one study, children with less than four months of misalignment demonstrated high-grade stereopsis once orthotropia was restored, whereas children who had greater than 11 months of misalignment did not recover any measurable stereopsis.20,35

Accommodative esotropia may also be associated with a high accommodative convergence to accommodation ratio (AC/A), due to excessive accommodative convergence. Bifocals with a +3.00 DS add can be used if there is a high AC/A ratio; they are best reserved for a child who is orthotropic in the distance but has a residual esotropia for near despite wearing the full hypermetropic correction.

Some children with an accommodative esotropia, especially those with a higher degree of hypermetropia, have a residual microesotropia (an esotropic flick measuring less than 10 PD on cover testing). This results in suboptimal vision and a tendency for amblyopia in the esotropic eye. Patching (occlusion therapy) of the fixing eye may therefore be required to improve the vision further in the squinting eye. Attempts to treat microtropia with eye exercises, anti-suppression, or prisms are likely to result in the previously asymptomatic child developing intractable diplopia. This is similar for residual microtropias following infantile esotropia surgery.19

Accommodative esotropia is generally a very stable strabismus when the full hypermetropic correction is given initially. Hypermetropia often decreases with age and there may be an increasing tendency for the eyes to drift out (consecutive exotropia). Hence long-term follow-up with periodic reduction in the degree of hypermetropia prescribed in glasses is recommended to maintain alignment and fusion.37

Partial Accommodative Esotropia

Sometimes children may have a residual esotropia, even with the full hypermetropic

Figure 4. Intermittent exotropia. A) Large exotropia in the distance. B) Orthotropic for near.

correction. The size of the strabismus is usually decreased with plus lenses and if the squint is alternating freely between the two eyes, amblyopia is unlikely to develop. However, if the child develops a fixation preference, then with time the squinting eye will become amblyopic. The goal of patching is to eliminate any amblyopia and to achieve alternation of squint, and this may be required for some years. Strabismus surgery can then be considered if an uncosmetic squint remains with the full hypermetropic correction, but is recommended after amblyopia has been successfully treated.

Non-Accommodative Esotropia

Some children with esotropia have little or no clinically significant hypermetropia and hence glasses cannot be used to improve the angle of the turn. Similar to other forms of esotropia, amblyopia may be the ongoing issue and patching required. Squint surgery is often required to improve alignment.

Any acute onset of esotropia, particularly beyond the typical age of presentation of an accommodative esotropia (toddler years), raises the concern of intracranial pathology. It is important to perform a full ophthalmic assessment to exclude a sixth nerve palsy / paresis and papilloedema, which can be signs of raised intracranial pressure. These children often proceed to magnetic resonance imaging (MRI) of the brain to exclude any underlying neurological condition.

Recently, an increase in cases of acute acquired concomitant esotropia (AACE) has been associated with prolonged use of electronic devices.38,39 Research is currently ongoing with regard to the pathophysiology, but AACE has been found to respond well to chemodenervation and surgery.

Intermittent Exotropia

Intermittent exotropia (IXT) is the most common type of exotropia,40 but the pathophysiology remains poorly understood.41,42

The divergent deviation is not present all the time, and more classically describes the pattern in which the exotropia is evident in the distance, particularly with inattention or fatigue, but the child remains orthotropic for near.

Management for intermittent exotropia can be conservative, i.e. continued observation, because the size of the deviation often remains reasonably stable,43-48 and decompensation to a constant exotropia is uncommon,46-48 if not rare.45 Treatment can involve minus overcorrection in glasses, exercises including antisuppression, patching or surgery. However, a natural history study of intermittent exotropia showed that IXT rarely resolved spontaneously.49

Less commonly, IXT may also present as a convergence weakness or insufficiency, where the eyes are orthotropic in the distance but a manifest exotropia is seen at near. The convergence insufficient type of IXT is responsive to orthoptic treatments aimed at improving motor and proximal fusion by strengthening fusional convergence amplitudes (e.g. with ramp and step exercises).

Similar to the established relationship between hypermetropia and esotropia, there is an association between myopia and exotropia32 whereby many children who have intermittent exotropia become myopic with time. In one population-based study of children with IXT, the likelihood of developing myopia was calculated to be over 90% by 20 years of age.50 Correcting the myopic refractive error helps control the deviation. In addition, overcorrecting with minus, generally by -2.50 DS or -3.00 DS, stimulates accommodative convergence, which can lead to fusion in the distance and increased control of the exotropia.51,52 Several studies have reported successful control of the deviation by overcorrecting with minus lenses compared to those without the overcorrection.51,52 Minus overcorrection is best tolerated in younger children, in view of their large accommodative range, and can sometimes act as a temporising measure prior to any consideration of surgery. A well-controlled intermittent exotropia has less risk of amblyopia.

Patching, either for amblyopia or antisuppression, has been noted by some authors to modestly decrease the magnitude of the angle of deviation in children with intermittent exotropia,53-55 while others did not find any change in angle size at follow-up.44,45,49 In some observational studies, reduction in the angle of exotropia over time has been reported in patients without treatment.46-48 This may simply reflect the well-known variability of the frequency and control of IXT56 or the test-retest reliability and possible measurement error that could occur, particularly evident in larger angles of squint.57

Anti-suppression exercises, such as with a red filter, are designed to make the child aware of a second image when one eye is turning, so they can attempt to fuse both images again. It should be mandatory that this is only given to children with intermittent deviations with good fusion potential, otherwise there is a real risk of inducing intractable diplopia.

Surgery is frequently undertaken for IXT43,49 and may not be a ‘cure’ but can improve cosmesis significantly, particularly if there are ongoing psychosocial concerns, although recurrence rates are high.58,59

RARER PATTERNS OF STRABISMUS

Less common forms of childhood strabismus, such as superior oblique palsy (fourth nerve palsy), Duane retraction syndrome (DRS), and Brown syndrome, present with distinct clinical features.

Congenital Superior Oblique Palsy

This is uncommon in children but typically presents with a head tilt to the opposite side of the paretic muscle. Often the squint developing due to the nerve palsy may not be evident initially and can take years to fully evolve. Hence any child with a head tilt without an obvious non-ocular cause, such as torticollis (a tight sternomastoid muscle in the neck), requires follow-up to see if the clinical signs of a superior oblique palsy are developing with time. For instance, a left-sided superior oblique palsy is likely to present with a right head tilt. A left over right vertical deviation (hyperphoria or hypertropia) may subsequently develop with a greater vertical deviation in right gaze and an increase in the vertical deviation when tilting the head to the left side. Eye movements will typically show a left inferior oblique overaction and superior oblique underaction. Squint surgery, generally directed at weakening the overacting inferior oblique, will often restore the vertical balance and eliminate the abnormal head posture.

Duane Retraction Syndrome

Duane retraction syndrome (DRS) is a congenital non-progressive eye movement disorder that is also uncommon but well recognised in childhood. Typical DRS is unilateral but sometimes can be bilateral, and there may be a family history. It is due to the lack of development of the sixth cranial nerve innervating the lateral rectus. An aberrant branch from the third cranial nerve then innervates the ipsilateral lateral rectus muscle. This means that both the medial rectus and lateral rectus are fired off when the Duane’s eye is adducting, causing retraction of the globe and narrowing of the palpebral fissure. Due to the absent / hypoplastic sixth cranial nerve, the Duane’s eye does not abduct well. Typically, the eyes are either straight in primary position or the Duane’s eye is slightly esotropic, often causing a face turn to the affected side. The amount of adduction / abduction simply reflects just how much of the sixth cranial nerve is actually present, and how much of the third cranial nerve is innervating the lateral rectus. Hence there can be various patterns noted and vertical upshoots and downshoots are common. Squint surgery is rarely required for DRS unless there is a significant face turn or a large angle esotropia in primary position, marked retraction on adduction, or uncosmetic upshoots and downshoots.

Brown Syndrome

This rarer non-progressive eye movement disorder is characterised by a lack of elevation in adduction of the affected eye. There can be congenital or acquired causes.

Congenital causes include a superior oblique tendon that is short, or a difficulty with the superior oblique tendon running through the trochlear complex. Sometimes spontaneous improvement can occur in the latter case. The child may present with a slight chin up posture to maintain binocular fusion in downgaze. A significant vertical deviation is noted in upgaze, particularly in adduction, with the affected eye being the hypotropic eye. Brown syndrome can sometimes be bilateral and very occasionally there is a family history. Generally, no treatment is required but indications for squint surgery include a significant head posture or a marked vertical deviation in primary position.

CONCLUSION

In summary, strabismus in children can be well controlled, but rarely cured. There is no role for vision therapy in the management of children with infantile esotropia. Early surgery is recommended in the hope that some stereoacuity can be recovered if the eyes are realigned. Prompt prescription of the full hypermetropic refractive error, as elicited with cycloplegia, in children with a likely accommodative esotropia gives the best chance to re-establish stereopsis and prevent amblyopia. In both infantile and accommodative esotropia, the duration of misalignment is the most critical factor with regard to stereoacuity outcomes. There remain no well-defined clinical guidelines or standardised regimen for the management of IXT, particularly with regard to observation versus intervention. A number of treatment options are available, including surgery. Antisuppression treatment for a constant tropia is likely to result in intractable diplopia. Other rarer patterns of strabismus occur in children, such as superior oblique palsy, Duane and Brown syndromes, with well recognised clinical features.

Dr Maree Flaherty MB BS (HONS) FRANZCO FRACS FRCOphth is a paediatric ophthalmologist who established the Children’s Eye Centre in Wentworthville over 30 years ago. She was a Senior Consultant Ophthalmologist at the Children’s Hospital Westmead for many years, involved in the multidisciplinary management of complex paediatric eye conditions and genetic eye disease. With more than three decades of experience, she has a particular interest in strabismus and has operated on many children with strabismus. She is a Clinical Senior Lecturer, Discipline of Ophthalmology, Sydney Medical School, University of Sydney and contributes to the ongoing education of ophthalmology, orthoptic, and optometry trainees.

Dr Flaherty acknowledges and thanks the orthoptists at the Children’s Eye Centre: Devica Apriyani, Irina Sim, Rosalyn Obra, and Wendy Liang, for their valuable contributions to this article.

References available at mivision.com.au.