Squints that come and go

The squint that comes and goes: intermittent exotropia

He only drifts outward when he is tired, staring into the distance, or has just woken up. That is not you imagining it, and it is the most common form of childhood squint, with its own pattern and its own plan.

by Dr Chan Li Yen · MBBS, MOphth (UM), Fellowship in Paediatric Ophthalmology & Strabismus

Practises at Hospital Kuala Lumpur 11 min read · 1,948 words

Key takeaways

Intermittent exotropia is an eye that turns outward some of the time while both eyes track straight the rest of the time, and it is the most common form of childhood-onset squint.
Classic triggers are tiredness, illness, distance viewing, and daydreaming; squinting or closing one eye in bright light often travels alongside it.
There is no guaranteed course. Some children's drift stays stable for years, some improve, and some worsen, which is why regular review rather than a single check is how it is followed.
Many children with a small, well-controlled drift are simply observed at intervals; glasses, patching or surgery are used when the measurements at review change, not automatically.
This pattern itself is not an emergency. A squint that appears suddenly and stays constant, or comes with a new head tilt or a sudden change in vision, needs prompt assessment instead.

He only drifts outward when he is tired, or staring into the distance, or has just woken up. That is not you imagining it, and it is not "nothing." An eye that turns outward some of the time and sits straight the rest of the time has a name, intermittent exotropia, and it is the most common form of childhood squint. I have already written about a squint that appears suddenly and stays constant, in sudden squint in a toddler, and about a strong eye quietly masking a weak one in the hidden weak eye. This is a different pattern again: one eye that comes and goes, most often outward, and is genuinely common rather than rare.

What actually is intermittent exotropia?

It is an eye that turns outward some of the time, while both eyes point straight and work together the rest of the time. It represents the most common form of childhood-onset squint, and it typically shows up most clearly during distance viewing, tiredness, illness, or moments of inattention, such as daydreaming.

Onset is usually early, most often between two and six years of age, though a good number of children are not actually noticed and diagnosed until school age, once someone, often a teacher or a photo, catches the pattern repeatedly rather than as a one-off.

It is worth saying plainly why this particular pattern unsettles parents more than a squint that is simply always there: a constant squint is at least consistent, so it is easy to believe and easy to act on. An eye that is straight in front of you one moment and drifting the next feels harder to trust, and harder to describe to someone who was not in the room to see it. That difficulty describing it is normal, not a sign you are imagining things or exaggerating, and it is exactly why doctors ask for detail rather than a single description: when it happens, how often, and whether it has changed recently.

Why does it only happen sometimes, and only in certain moments?

Parents typically describe the same handful of triggers: the eye drifts when the child is tired, unwell, or gazing into the distance, and stays straight the rest of the time. A second sign often travels alongside it: a child who squints or closes one eye in bright sunlight. That is not a separate quirk, it is the child's own way of blocking out double vision when the eyes are not lined up, and it is common enough to be considered part of the same pattern rather than a coincidence.

The eyes drifting apart, rather than crossing inward, is the specific direction that defines this condition, distinct from the inward-turning squints covered elsewhere on this site. Recognising which direction an eye turns, and that it comes and goes rather than staying constant, is exactly the kind of detail worth describing precisely to your doctor, because it helps place a child correctly within a condition that behaves differently from a squint that is there all the time.

Does the type of drift matter?

Doctors classify intermittent exotropia by comparing how much the eye drifts when the child is focusing on something close versus something far away. In most children the drift is roughly similar at both distances, called the basic type. In others, the drift is noticeably worse at near, called convergence insufficiency, or noticeably worse at distance, called divergence excess.

This is not something to work out at home, and it does not change what a parent should do day to day; it is simply the kind of measurement a doctor takes at a proper assessment, because it shapes which nonsurgical option, if any, is likely to help most.

Will this get worse over time?

There is no single, guaranteed answer, and it would not be honest to give one. Older research following untreated children found that most showed some progression over time, a minority stayed stable, and a smaller group actually improved. More recent work following children found a somewhat different split: just over half stayed stable, close to a fifth improved, and just under a quarter worsened.

Those two findings do not agree on an exact number, and that is precisely the point: the course of intermittent exotropia genuinely varies between children, and there is no fixed timeline or guaranteed direction. What can be said with confidence is that regular review, rather than a single check, is how a doctor tells which pattern a particular child is following, by watching how the control and the angle of the drift change, or do not change, from one visit to the next.

Does my child need surgery, glasses, or a patch?

Often, none of the above straight away. A small, well-controlled drift that a child can pull back into line easily, with normal depth perception between visits, is frequently simply observed, with review at set intervals rather than immediate treatment. Where treatment is used, it usually starts with the least invasive option that fits the child: correcting any short-sightedness or significant astigmatism with glasses, orthoptic exercises in some cases, or part-time patching.

Patching deserves a specific, honest mention, because it is often assumed to be clearly superior to simply watching and waiting, and the evidence does not fully support that assumption. One trial comparing children who were patched for a set period each day against children who were simply observed found a similarly low rate of the condition worsening in both groups over six months, suggesting that both a watch-and-review approach and patching are reasonable options for many children, rather than one being clearly the right answer and the other a lesser choice.

Surgery is reserved for a different picture: a drift that is becoming more frequent, control that is visibly slipping, or a fall in how well the two eyes work together as a measurable pair, of the kind I describe generally in how two eyes work together. None of these decisions are made from a single glance in a waiting room; they come from measurements taken and compared over more than one visit.

When does this pattern need a same-day assessment rather than the next routine visit?

Intermittent exotropia itself is not an emergency, and most children with this pattern are simply followed over time. What does deserve prompt attention is a squint that appears suddenly and is constant rather than coming and going, a squint accompanied by a new head tilt, or any sudden change in how well your child seems to see, since those point towards a different and more urgent picture than a squint that has been intermittent for some time. The distinction between an intermittent squint and a new, constant one is drawn out in more detail in the sudden squint article linked above, and is worth reading alongside this one if you are not yet certain which pattern you are seeing.

Outside of that distinction, an outward drift that shows up only when your child is tired, unwell, or staring into the distance, and otherwise sits straight, is a real and recognised pattern. It is not a reason to panic, and it is also not a reason to wait indefinitely before having it properly assessed and, from there, reviewed at the intervals your doctor sets.

A phone video, taken at the moment you notice the drift rather than recreated afterwards, is often more useful at that first assessment than a description alone, precisely because the pattern is intermittent and may not show itself on demand in a clinic room. Note roughly how often it happens, and whether it seems to be becoming more frequent over weeks rather than staying about the same, since that trend, more than any single observation, is what guides whether watching, glasses, patching, or eventually surgery is the right next step for your particular child.

Don't wait for a check-up if…

A squint appears suddenly and is constant, rather than coming and going.
The outward drift is accompanied by a new head tilt.
Your child's vision seems to have changed suddenly, or they complain of double vision.
The drift is becoming clearly more frequent over a matter of weeks, rather than staying about the same.
Your child has never had an eye assessment and you have noticed any pattern of drifting, even an intermittent one.

Common questions

What is intermittent exotropia?

It is an eye that turns outward some of the time, while both eyes point straight and work together the rest of the time. It is the most common form of childhood-onset squint, and it typically appears most clearly during distance viewing, tiredness, illness, or moments of inattention.

At what age does intermittent exotropia usually start?

Onset is usually early, most often between two and six years of age. A good number of children are not actually noticed and diagnosed until school age, once a teacher or a repeated photo pattern draws attention to it.

Why does my child's eye only drift outward sometimes?

Classic triggers are tiredness, illness, gazing into the distance, and daydreaming. A child squinting or closing one eye in bright sunlight is a related sign, a way of avoiding double vision when the eyes are briefly not lined up, and it commonly travels alongside the drift.

Will intermittent exotropia get worse over time?

There is no guaranteed course. Different studies following untreated children have found different splits between children who stayed stable, improved, or worsened over time, and no single number applies to every child. Regular review, watching how the control and angle of drift change over more than one visit, is how a doctor tracks a particular child's pattern.

Does my child need surgery for this?

Often not, at least not immediately. A small, well-controlled drift with normal depth perception is frequently simply observed at set review intervals. Surgery is reserved for a drift that is becoming more frequent, with visibly slipping control or a measurable fall in how well the two eyes work together, decided from measurements taken over more than one visit, not from a single glance.

Does patching help with intermittent exotropia?

It can be one reasonable option, but it is not clearly superior to simply observing and reviewing. A trial comparing daily patching against observation alone found a similarly low rate of worsening in both groups over six months, so both are considered reasonable approaches for many children rather than one being the clearly correct choice.

How is intermittent exotropia different from other squints on this site?

This pattern is specifically an outward drift that comes and goes, distinct from a squint that appears suddenly and stays constant, which is covered separately, and from a strong eye masking a weaker one, covered in the site's article on the hidden weak eye. The direction of the turn and whether it is constant or intermittent both matter to how it is assessed.

When should I take my child to a doctor urgently about a squint?

See a doctor promptly for a squint that appears suddenly and stays constant rather than coming and going, one that comes with a new head tilt, or any sudden change in your child's vision. An intermittent outward drift that has been present for a while, without those features, still deserves a proper assessment, just not as a same-day emergency.

References

StatPearls (NCBI Bookshelf) · Intermittent Exotropia · www.ncbi.nlm.nih.gov
AAPOS · Exotropia · aapos.org
American Academy of Ophthalmology · Intermittent Exotropia (disease review) · www.aao.org
EyeWiki (American Academy of Ophthalmology) · Intermittent Exotropia · eyewiki.org

By Dr Chan Li Yen. General information only. It does not replace a consultation. If you are worried about your child's eyes or vision, please see an eye doctor.