Why it happens

A newborn's eyes are not yet a team. The AAP explains the mechanism: most visual development happens in the brain rather than the eyes, and one of the hardest jobs for a developing brain is coordinating signals from both sides. Until that coordination arrives, the eyes can point in slightly different directions when a baby is tired, is looking at nothing in particular, or is looking past you rather than at you.

The AAP puts a timescale on the earliest stage: "For the first 2 to 4 weeks of life vision is not accurate enough for the baby's eyes to find a target a lot of the time. Parents often feel like their newborns are looking past them rather than at them, because they are. By the fourth week of life, however, your baby will focus on your face if you're cradling him."

The NHS says the same thing in one line on its newborn page: "Your newborn's eyes may roll away from each other occasionally. This is called a squint and is normal in a newborn."

How long it is meant to last

Here the sources give two slightly different numbers, and both are worth having.

The NHS newborn page: a newborn squint "should go away by 4 months. Talk to your health visitor or GP if it does not."
The NHS squint page: get advice if your child is older than 3 months and has a squint that comes and goes — "in babies younger than this, squints that come and go are common and are not usually a cause for concern". And get advice at any age if the squint is there all the time.
The AAP: occasional crossing "for the first 6 months of life... can be normal", but by two months a baby should be able to track a face or toy from right to left and back again, and by six months the eyes should stay aligned even if one is briefly covered.

The safest reading of all three is the strictest one. If the eyes are misaligned all the time, that is worth raising now, at any age. If they drift sometimes, expect it to be settling by around three to four months, and raise it if it is not.

What is normal in the meantime

The AAP's account of vision development gives the reference points:

Newborn: can see light, shapes, faces and movement. Distance vision is blurry. Focus is best at about 20 to 30cm (8 to 12 inches) — roughly the distance from your baby's eyes to yours during a feed.
Wandering: the AAP says a newborn's eyes may occasionally wander, cross or move randomly, and that this "random movement should be going away by 2 to 3 months of age".
By 3 months: babies should focus on faces and close objects and follow a moving object with their eyes.

The HSE's eyesight timeline is compatible: from birth to six weeks a baby starts to focus their gaze on a face or object; by six to eight weeks they may look at you, follow your face, smile back when you smile, follow a coloured toy at about 20cm, and move both eyes together. That last item is the one that matters on this page.

The eyes that only look crossed

The AAP flags a common false alarm: "Sometimes the shape of a child's face makes it look as though the eyes are crossed even when they are not. A child with a broad nasal bridge may appear to have an inward-looking eye, when in fact he's just looking off to the side." The AAP gives a simple home check: "watch the light reflection in your child's eyes from a window or lamp; if it falls in the same place on each eye, the eyes are working together." Photographs taken straight on, without flash red-eye, are a good way to look at this calmly.

Why the deadline matters

The NHS is blunt about this and it is the reason not to wait it out: a squint that is constant, or that develops after three months of age, "is unlikely to get better on its own and it could cause further problems if not treated early on." The named risk is amblyopia, or lazy eye, where "the brain starts to ignore signals coming from the affected eye, so your child does not develop normal eyesight".

The NHS adds that surgery can improve alignment even after a long delay, "but any vision problems may be permanent if they are not treated at a young age". The AAP makes the same point: over time the brain's suppression of the weaker eye becomes irreversible.

Treatments the NHS lists include glasses if the squint is driven by long-sightedness, eye exercises, surgery to reposition the eye muscles, and injections into the eye muscles — and if there is a lazy eye as well, that is usually treated first, often with patching.

The checks your baby already gets

The NHS's newborn physical examination, offered within 72 hours of birth, includes the eyes, and it is repeated at around six to eight weeks. NICE's postnatal care guideline NG194 specifies exactly what is looked at: opacities, the red reflex and the colour of the sclera. That red reflex check is looking for things like congenital cataract, which is why it is done with a light rather than by watching how the eyes move.

The HSE lists the signs of an eye problem in younger children as: a baby over six to eight weeks who does not fix on and follow an object one to three metres away; eyes that are not looking in the same direction; not learning to respond to facial expressions, for example not smiling; not reaching for objects; sensitivity to light even when it is not bright; rubbing the eyes; and eyes that seem very large or prominent.

When to call

Speak to your health visitor, public health nurse, GP or optician if:

One eye turns in, out, up or down all the time, at any age.
A squint that comes and goes is still there after three months, or has not gone by four months.
Your baby regularly turns their head to one side to look at things, or keeps one eye closed.
Your baby is not fixing on and following your face by six to eight weeks.
The white of one eye looks different, or a pupil looks white or cloudy, or looks white in a flash photograph — ask for this to be looked at promptly.
Your baby's eyes seem very sensitive to light, or one eye looks larger than the other.

The NHS also notes that a squint can rarely be a symptom of retinoblastoma, a rare childhood eye cancer, which is exactly why it says to see a GP about a squint rather than waiting for it to resolve.

What to let go of

Eye exercises you find online, patching without a diagnosis, and toys marketed to fix eye tracking are all beside the point. The two useful things are to hold your baby's face at about 20 to 30cm so there is something in focus to look at, and to get a persistent squint looked at inside the window where treatment still changes the outcome.

Newborn Eyes Crossing