Babies & first checks

One of my baby's eyes looks smaller than the other

One eye looks smaller in a photograph, or when you look down at your baby's face. The eye itself is only one of four places the difference can come from. How to tell them apart, and which ones should not wait.

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

Dr Chan Li Yen, consultant paediatric ophthalmologist, MMC 43128, NSR 132980 · Eagle Eye Centre Kuala Lumpur, Petaling Jaya

11 min read · 1,996 words

Key takeaways

An eye can look smaller because the upper lid sits lower, because the face is fuller on one side, because the other eye is the larger one, or, less often, because the eye itself is small.
A head flattened on one side can make the eye on that side look bigger, which leaves the other looking smaller. Guidelines say the shape usually improves as a baby moves and sits.
A lid that sits low can affect vision, so a paediatric eye doctor should check it. A large eye that is also cloudy, watery or sensitive to light should be examined soon, as it can be a sign of childhood glaucoma.
A truly small eye (microphthalmos) is described as rare, and sight ranges from little affected to significantly reduced. Only an examination can say which.
Take a straight-on photograph in daylight every week or two and bring them to the appointment. A photograph alone cannot tell the causes apart.

One eye looks smaller than the other. You notice it in a photograph, or when your baby is feeding and you are looking straight down at the face. In Malay the search is "mata bayi kecil sebelah", and the worry behind it is the same: is this an eye problem, or just a face?

The honest answer is that "smaller" can come from four different places, and only some of them are the eye. Below is how I sort them, what each one looks like, and which ones should not wait for a routine appointment.

Is one of my baby's eyes really smaller, or does it only look that way?

Very often it only looks that way, and the difference comes from the lid, the face or the other eye rather than from a small eye. The opening between the lids can look smaller because the lid sits lower, because the cheek and forehead on one side are fuller, or because the other eye is the larger one. A truly small eye exists, but the sources describe it as rare.

That is why a photograph on its own settles very little. The same baby can look uneven or even depending on the angle of the phone and the way the head is turned. What settles it is an examination that looks at the lids, the eyes and the shape of the face together.

Noticing it is not a sign you missed something. It is what the examination is for.

Could it be the eyelid rather than the eye?

Yes, and the lid is a good place to look first. If one upper lid sits lower, it covers more of the eye and the opening looks smaller. When a baby is born with a lid like that, it is called congenital ptosis. The American Association for Pediatric Ophthalmology and Strabismus (AAPOS) explains it as a weak lid-lifting muscle, which in children usually starts before birth.

The reason it matters is what the lid can do to vision, not how it looks. AAPOS lists astigmatism from the lid pressing on the eye, a chin-up head position to see under the lid, and a lazy eye (amblyopia) when vision does not develop well. In severe cases the lid can block vision. A paediatric eye doctor checks the lid position, the vision, whether glasses are needed and the head position. The full picture is in the article on droopy eyelids in babies.

If the pupils also look different in size, that is a separate question with its own article, one pupil bigger than the other.

Could the flat spot on my baby's head be the reason?

It can be. A head that is flattened on one side at the back (positional plagiocephaly) can make the face uneven. The Royal Children's Hospital in Melbourne describes the eye on the affected side as possibly looking bigger, with the cheek pushed forward and the ear pushed forward on the same side. The American Academy of Family Physicians describes the forehead as more prominent on that side, and Cleveland Clinic lists a forehead, eye or cheek that looks larger or fuller on one side.

Notice what that means. In this case the eye that looks big is the flattened side, and the other eye looks smaller only by comparison. Neither eye needs to be at fault.

Head shape is assessed by your baby's doctor or nurse, and I am not suggesting any change to how your baby sleeps. The Melbourne guideline advises arranging the room so your baby turns toward the less flat side while awake, with toys placed on that side, and regular tummy time. It also says the shape improves once babies can move their head on their own, and that it usually settles without treatment by the time a baby sits without support. It advises referral if the deformity is severe or worsening despite these steps, if a ridge along a skull seam is suspected, or if a tight neck is not improving.

The eye check still has a place here, because a flat head does not rule out a lid or eye cause at the same time. See when a baby should have a first eye check.

Which eye is the problem, the small one or the big one?

Sometimes it is the bigger eye. An eye that is enlarging can make its partner look small, and in babies an enlarging eye is one of the reasons doctors think of childhood glaucoma, a condition where the pressure inside the eye is too high. AAPOS lists the signs in babies as too much tearing, eye pain with bright light, and a large or cloudy cornea, which is the clear front of the eye. Its advice is that a child with these symptoms should see an eye doctor, and that early diagnosis and regular follow-up matter for protecting vision.

Watery eyes on their own are usually a blocked tear duct, and AAPOS makes that point itself, which is why an examination is needed to tell the two apart. But an eye that looks larger, and is also cloudy, watery or seems to hate light, should be examined soon rather than at the next routine slot. The longer explanation is in big beautiful eyes can be a warning sign.

Before you decide which eye is smaller, decide which one is different.

Can an eye really be small, and what does that mean for sight?

Yes, but it is uncommon. A small eye is called microphthalmos (microphthalmia), a developmental condition in which one or both eyes are smaller than usual. MedlinePlus Genetics gives a frequency of about 1 in 7,000 people. EyeWiki calls it rare and notes it may affect one eye, though it is more commonly both.

What it means for sight varies a great deal, and no one can tell from a photograph. MedlinePlus says people with it may or may not have significant vision loss, and EyeWiki explains that the outlook depends on which parts of the eye are affected. Good vision may be kept in some children, while involvement of the macula (the centre of the retina) or the optic nerve is linked with poor vision. Some children also have other conditions, so the doctor looks at the whole child.

The examination measures the eye, including the size of the cornea, and may add scans. A baby whose eye has looked very small since birth should have that examination without waiting for a routine slot.

When does it need an eye check this week?

Book within days, rather than at the next routine visit, if any of these is present. The lid covers part of the pupil. Your baby tips the chin up or works the eyebrow hard to look out from under a lid. The larger eye is cloudy, watery or avoids light. One eye has looked very small since birth. Or the difference is new, having appeared or clearly changed over days or weeks.

If the difference is mild and stable, there is no sign of any of the above, and the flat-head explanation fits, it is still worth an examination to be sure, but it is not an emergency. A routine check can be arranged through a klinik kesihatan or a family doctor, and who checks a child's eyes explains the routes.

Will it even out, and what can I do until the appointment?

That depends on the cause, and I cannot promise it for any one baby. If it is the flat head, the shape usually improves as a baby moves and sits, according to the Melbourne guideline, and the face would be expected to look more even with it. A lid, a large eye or a small eye needs an examination, not a wait.

While you wait, take a photograph straight on, in daylight, with your baby's face level and looking towards you, and repeat it every week or two. Make a note of whether the lid ever covers the pupil, whether the eye waters, whether your baby seems bothered by light, and whether the difference looks the same in every photograph. Take the photographs with you. They give the doctor something to compare against.

Above all, keep the appointment. A small difference that is nothing is a good result, and a small difference that is something is found earlier.

Do not wait for a routine visit if…

The upper lid covers part of the pupil, or your baby tips the chin up or works the eyebrow hard to see.
The eye that looks larger is also cloudy, watery or seems to hurt in bright light.
One eye has looked very small since birth.
The difference is new, or is clearly changing over days or weeks.

Common questions

Why does one of my baby's eyes look smaller than the other?

Usually because of the lid, the face or the other eye, not because the eye itself is small. A lower upper lid covers more of the eye, a flattened head can make the face fuller on one side, and an enlarged eye can make its partner look small. A truly small eye is described as rare. An examination sorts these out; a photograph cannot.

Could my baby's flat head make one eye look different?

Yes. A head flattened on one side at the back can make the forehead, cheek and eye on that side look larger or fuller, and the ear sits further forward. The Royal Children's Hospital Melbourne guideline says it usually improves once babies can move their head themselves. Ask your baby's doctor or nurse about head shape, and still have the eyes checked.

Is it normal for one eyelid to be lower than the other?

I cannot tell you that from a description, because a lower lid can be a droopy lid (ptosis) that affects vision. AAPOS says a lid that droops can cause astigmatism, a chin-up head position and a lazy eye, and that a paediatric eye doctor should assess it. Book an examination rather than waiting to see.

When should I take my baby to an eye doctor for this?

Within days if the lid covers the pupil, if the larger eye is cloudy, watery or sensitive to light, if one eye has looked very small since birth, or if the difference is new or changing. If it is mild, stable and fits a flat head, an examination is still sensible, but it is not an emergency.

What is microphthalmos?

It is a developmental condition in which one or both eyes are smaller than usual. MedlinePlus Genetics gives about 1 in 7,000 people. Sight can range from little affected to significantly reduced, depending on which parts of the eye are involved, so the doctor examines the eye and the whole child.

Will the difference even out by itself?

It depends on the cause, and I cannot promise it for any one baby. If it is the flat head, the shape usually improves as the baby moves and sits. A low lid, an enlarged eye or a small eye needs an examination, not a wait.

What should I bring to the appointment?

Photographs taken straight on, in daylight, with your baby's face level, over a few weeks. Also note whether the lid ever covers the pupil, whether the eye waters, whether light seems to bother your baby, and whether the difference looks the same in every photograph.

References

American Academy of Family Physicians · Positional plagiocephaly (American Family Physician, 2003) · www.aafp.org
Royal Children's Hospital Melbourne · Positional plagiocephaly, clinical practice guideline · www.rch.org.au
Cleveland Clinic · Plagiocephaly (flat head syndrome) · my.clevelandclinic.org
EyeWiki (American Academy of Ophthalmology) · Microphthalmos · eyewiki.org
MedlinePlus Genetics · Anophthalmia and microphthalmia · medlineplus.gov
American Association for Pediatric Ophthalmology and Strabismus · Ptosis · aapos.org
American Association for Pediatric Ophthalmology and Strabismus · Glaucoma in children · aapos.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.