Warning signs

Two different-coloured eyes: when it is genetics and when it needs a same-day look

A parent notices it in a photograph first, almost every time: one eye reads a shade lighter than the other. Most of the time this is heterochromia, ordinary and genetic. A short list of things alongside it changes that answer.

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

Practises at Hospital Kuala Lumpur 11 min read · 1,971 words

Key takeaways

Heterochromia, two different iris colours in the same child, is usually benign and genetic, with nothing else wrong.
AAO's own baseline advice is that any infant with heterochromia is examined by an eye doctor at least once, even when nothing else looks amiss.
A drooping eyelid or a smaller pupil on the lighter-eye side can mean Horner syndrome; a white forelock, patchy pale skin or a failed hearing test alongside it can mean Waardenburg syndrome.
An iris that changed colour after birth, rather than being two colours from the start, is a different and more urgent pattern than the genetic kind.
Photographs under flash or mixed lighting often make one iris look different from the other; a genuine difference is the same in daylight and in the mirror.

It is almost always a photograph that starts it. Parents often notice it first when scrolling back through pictures, one eye reading a shade lighter than the other, sometimes only in one particular light. What they have usually found is heterochromia: two eye colours in the same child, with nothing else going on.

I want to give you that reassurance honestly, not as a way of rushing past the question. Heterochromia is not rare, and it is usually harmless, with the overwhelming majority of children who have it going on to have completely healthy eyes. What this article is for is the short, real list of things that can sit alongside two eye colours and turn a cosmetic observation into something to look at this week, so you know which kind you are looking at.

What actually is heterochromia?

It is simply two irises that are different colours, or one iris that has more than one colour within it. Doctors describe three patterns: complete, where one whole iris differs from the other; sectoral, where part of one iris differs from the rest of that same eye; and central, where a ring closer to the pupil differs from the outer part of the iris. If it is there from birth or appears in the first weeks of life, it is called congenital. If a child's eyes were the same colour and one visibly changes later, that is acquired, and it is a different, more urgent pattern that I come back to below.

Does two-colour eyes mean something is wrong?

No, in the great majority of children. Benign heterochromia, the kind with no underlying condition at all, is the most common form there is. That said, the standard advice from the American Academy of Ophthalmology is that any infant found to have heterochromia is examined by an eye doctor at least once, because it can, uncommonly, be the first visible sign of a small number of named conditions. Most of those examinations end with nothing else found, and I would still rather you had that one appointment and the reassurance on record than skip it because the odds are good.

What is Horner syndrome, and why does a droopy lid matter here?

Horner syndrome is a specific combination: a drooping upper eyelid, a pupil that is smaller than the other one, most noticeable in dim light, because the affected pupil fails to widen normally in the dark, and reduced sweating on that side of the face. When this pattern is present from birth, the affected iris is often paler too, because the same nerve pathway that carries the drooping lid and small pupil also guides how colour develops in the iris during early life. On its own, a slightly drooping eyelid is common and usually nothing. Paired with a smaller pupil and a lighter iris on the same side, it is the combination worth an eye doctor's look, because congenital Horner syndrome occasionally points to something further along that nerve pathway that benefits from being found early.

What is Waardenburg syndrome, and what does it look like alongside heterochromia?

Waardenburg syndrome is a genetic condition present from birth. Along with heterochromia, the features to know are a white forelock, a patch of hair with no pigment usually at the front hairline, patches of unusually pale skin, and congenital hearing loss that is usually present from birth and usually does not worsen. It is one of the recognised genetic causes of childhood deafness. None of these features on its own proves anything, but heterochromia appearing alongside a white forelock, patchy pale skin, or a failed newborn hearing screen is worth naming to your child's doctor directly, because the hearing loss it can carry is the part that benefits most from being caught early, long before it would otherwise be noticed.

My child's eye changed colour after birth. Is that different?

Yes, and it is the pattern I would want to see sooner rather than later. A colour that was the same at birth and has genuinely changed since is called acquired heterochromia, and the causes are a different list: injury to the eye, inflammation inside the eye, and a rare but recognised growth in young children called juvenile xanthogranuloma, which can involve the iris and cause it to change colour, sometimes with a red or teary eye, or blood appearing at the front of the eye with no injury at all. An iris colour that changes after your child's first year, particularly with any of those other signs, is not the same question as a baby born with two eye colours, and deserves prompter attention.

Could this just be the camera, not a real difference?

Often, genuinely yes. Flash photography and mixed indoor lighting can make one iris look noticeably lighter or darker than the other in a single picture, and this catches parents out, especially in the first year of life when a baby's true eye colour is still settling as pigment develops. Before you worry, look in daylight, and look again in the mirror over a few days rather than trusting one photo. A genuine difference looks the same in every kind of light your child sits in. A trick of the flash does not, and usually disappears the moment you look properly.

What happens at the appointment if we come in for this?

Very little that would trouble your child. I look at the pattern and extent of the colour difference, check the eyelids sit evenly and the pupils are equal and react normally to light, and ask a few questions about hearing, skin and hair from birth, and about any injury or eye redness if the colour seems to have changed. For most children that is the whole visit, and most examinations find nothing else. I go through what a general eye check for a young child actually involves, step by step, in how we test children's eyes before they can read, which is worth reading before any first appointment so nothing about it feels unfamiliar. If anything about the pupils themselves looks uneven rather than the iris colour, that is a related but separate sign covered in one pupil bigger than the other, and worth reading alongside this one if that is closer to what you have noticed.

So what should I actually do?

If your child has had two eye colours since babyhood, with straight eyelids, equal pupils, normal hearing and no redness, that is very likely the benign, genetic kind, and a routine mention at the next check-up is reasonable. If you notice a droopy lid, a smaller pupil on the lighter side, a white forelock, patchy pale skin, a failed hearing screen, a colour that has changed since birth, or any redness or blood in the eye alongside it, that is worth an appointment this week rather than at the next scheduled visit. Either way, this is one of those findings where a single proper look, once, is worth more than months of checking photographs against each other. A change in the coloured part of the eye is a different sign from a white glow appearing in a photo's pupil, which is its own, more urgent warning sign covered in the white glow in photos, and worth knowing apart from this one.

See an eye doctor this week if…

The lighter eye also has a drooping eyelid or a pupil that looks smaller than the other, especially in dim light.
There is a white patch of hair, patchy pale skin, or your child has not passed a newborn hearing screen.
The iris colour was the same at birth and has changed since, particularly with a red, teary or irritated eye.
You see any blood in the front of the eye that was not there before, with no known injury.
The colour change followed a known injury to the eye, or comes with a persistently red, painful or light-sensitive eye.

Common questions

Is it normal for a baby to have two different-coloured eyes?

Yes, most of the time. Heterochromia, where the two irises are different colours, or one iris has more than one colour in it, is usually a benign genetic trait with no underlying condition at all. It is uncommon rather than rare, and on its own is not a reason to worry.

Should my baby still be checked if the eyes just look like two different colours and nothing else seems wrong?

The American Academy of Ophthalmology's own baseline advice is that any infant with heterochromia is examined by an ophthalmologist at least once, precisely because it can, uncommonly, be the first visible sign of a few named conditions. Most of those checks confirm nothing else is going on, and that reassurance is worth having on record.

What is Horner syndrome, and why does it matter here?

Horner syndrome is a pattern of a drooping upper eyelid, a smaller pupil on that same side, and reduced sweating on that side of the face. When it is present from birth, the affected iris often ends up a lighter colour, because the same nerve pathway that is disrupted also guides colour development in the iris. Heterochromia appearing with a droopy lid or an unequal pupil is the specific combination that moves this from cosmetic to something worth imaging and investigating.

What is Waardenburg syndrome?

It is a genetic condition present from birth that can include heterochromia alongside a white forelock, patchy pale skin, and congenital hearing loss that is usually present from birth and usually does not worsen. It is one of the recognised genetic causes of childhood deafness, which is why heterochromia alongside any of those other features is worth a proper assessment rather than being put down to eye colour alone.

My child's eye was one colour at birth and seems to have changed since. Is that different from being born with two eye colours?

Yes, and it is the more urgent pattern of the two. A colour that changes after birth, rather than being present from the start, can be a sign of acquired causes including a rare growth called juvenile xanthogranuloma, injury, or inflammation inside the eye. Any acquired change, especially alongside a red, teary or irritated eye or any blood visible at the front of the eye, should be seen promptly rather than watched.

Could this just be the flash in a photograph, not a real difference?

Often, yes. Camera flash and mixed indoor lighting can make one iris look noticeably lighter or darker than the other in a single photo, especially in babies whose eye colour is still settling in the first year. Check in daylight and in the mirror over a few days. A genuine difference looks the same in every kind of light; a photo artefact does not.

Does heterochromia affect how well my child sees?

On its own, no. The colour of the iris does not affect vision. If heterochromia turns out to be linked to one of the conditions named above, it is that underlying condition, not the eye colour itself, that can carry its own effects, which is exactly why the assessment matters more than the colour.

At what age does eye colour finish settling in babies, and could that explain what I am seeing?

Many babies are born with eyes that look blue-grey and darken over the first six to twelve months as pigment develops, and that settling can happen at slightly different rates in each eye before evening out. This is a normal, temporary process and is different from a lasting, stable difference between the two eyes seen well past a child's first birthday, which is the pattern this article is about.

References

American Academy of Ophthalmology · What Is Heterochromia? · www.aao.org
PMC case report · Congenital Horner Syndrome with Heterochromia Iridis Associated with Ipsilateral Internal Carotid Artery Hypoplasia · pmc.ncbi.nlm.nih.gov
NORD (National Organization for Rare Disorders) · Waardenburg Syndrome · rarediseases.org
CMAJ case report · Heterochromia caused by Waardenburg syndrome in a 2-month-old infant · www.cmaj.ca

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.