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Coloboma: What It Is, Types, Causes, Symptoms and Treatment
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Coloboma (noun, plural colobomas or colobomata): a coloboma is a gap in the eye, present from birth, where part of the normal tissue is missing. It happens when a seam in the developing eye fails to close in early pregnancy, and it can affect the iris (giving a "keyhole" pupil), the retina and choroid, the optic nerve, the lens or the eyelid. Vision can be normal or reduced, depending on where the gap is and how large it is; the gap itself cannot be repaired, but many complications can be treated.
Coloboma: key facts
- What it is
- A congenital (from birth) gap in eye tissue; the word comes from the Greek for "mutilated" or "with a defect"
- Cause
- Incomplete closure of the optic (embryonic) fissure in early pregnancy, usually in the first two months
- Where
- Typically the lower, inner (inferonasal) part of the eye; one or both eyes
- How rare
- About 1 in 10,000 people (MedlinePlus); published estimates of 0.5–2.2 per 10,000 live births for ocular coloboma
- Types
- Iris, lens, chorioretinal (retina and choroid), optic nerve, eyelid
- Inheritance
- Often no family history; can be inherited (dominant, recessive or X-linked), and can be part of a syndrome such as CHARGE
- Main risk
- Retinal detachment when the retina or choroid is involved; amblyopia ("lazy eye") in children
- Cure
- No. The gap stays, but glasses, lenses, laser, surgery and low-vision support manage its effects
- Specialist
- Ophthalmologist, ideally with retina experience; at Laser Istanbul Clinic, Doç. Dr. Muhammet Derda Özer (retina, cornea, cataract) and Op. Dr. Aysan Bayram (retinal disease)
What is a coloboma of the eye?
A coloboma of the eye is a congenital defect in which a piece of the eye's structure is missing. The American Academy of Ophthalmology describes it as normal tissue in or around the eye that is missing at birth. It can involve the eyelid, iris, lens, ciliary body, the zonules that hold the lens, the choroid, the retina or the optic nerve, and EyeWiki notes it most often sits in the lower, inner (inferonasal) quadrant and is often linked with an unusually small eye (microphthalmia).
Many people first meet the word because an iris coloboma is visible: the pupil is not round but pear- or keyhole-shaped, a bit like a cat's eye. Others have a coloboma at the back of the eye that nobody sees from the outside, and it is found at an eye test. The same term, "coloboma", is used for all of these, which is why the effect on vision ranges from none at all to severe.
Types of coloboma
The type depends on which part of the eye is affected, and one person can have more than one.
| Type | What is missing or affected | What it looks like or does |
|---|---|---|
| Iris coloboma | A segment of the iris, usually at the bottom | A keyhole or cat-eye pupil; glare and light sensitivity are common |
| Chorioretinal coloboma | Part of the choroid and retina at the back of the eye | Often unseen from outside; a blind patch (field defect) in the vision; risk of retinal detachment |
| Optic nerve coloboma | A gap or hollow in the optic nerve head | Reduced vision, depending on how much of the nerve is involved |
| Lens coloboma | A notch or flattening at the edge of the lens | The lens tissue is not truly missing; the problem is in the supporting fibres (zonules). It can blur vision |
| Eyelid coloboma | A notch in the lid, most often at the inner third of the upper lid | The lid does not cover the eye fully, so the cornea can dry out and be damaged |
The iris is the most commonly affected site, and these gaps are often found together: an iris coloboma can go with a coloboma of the ciliary body, choroid, retina or optic nerve. Because of that, a child or adult with an iris coloboma should always have the back of the eye examined as well.
What causes coloboma?
Colobomas happen when the optic fissure does not close properly during early eye development. In the womb, the eye forms as a cup with a seam along its underside. That seam normally closes during roughly the fifth to seventh week of pregnancy; if it stays partly open, a gap remains. If the gap is at the front, it affects the iris; if at the back, the choroid, retina or optic nerve.
What makes the seam fail to close is not always clear. The known causes are:
- Genes. MedlinePlus lists more than 40 genes linked to coloboma, including PAX6, OTX2, CHD7, SOX2 and BCOR. Most cases occur with no family history. When it does run in families it can be passed on in a dominant, recessive or, less often, X-linked pattern.
- Syndromes. Coloboma is part of several syndromes, the best known being CHARGE syndrome (the C stands for coloboma, along with heart, nasal airway, growth, genital and ear differences). EyeWiki reports changes in the CHD7 gene in about 70–90% of people who meet the diagnostic criteria for CHARGE. Others include Treacher Collins, Goldenhar and cat-eye syndromes and trisomy 13 and 18.
- Environment. MedlinePlus notes that factors such as alcohol exposure during pregnancy may increase risk. A Texas birth-registry study of 1,587 children with coloboma (1999–2014) also found higher prevalence with multiple births and maternal diabetes. These are statistical associations, not proof that any one pregnancy caused it.
- Unknown. Many cases have no identifiable cause. Nothing a parent did or did not do is usually to blame.
In the same Texas study, about 59% of children had a non-syndromic coloboma and about 30% had it in isolation, with no other birth defect, which means a good share of children with coloboma do have other differences and need a wider check-up.
How rare is coloboma?
Coloboma is rare. MedlinePlus puts it at about 1 in 10,000 people, and EyeWiki quotes 0.5–2.2 cases per 10,000 live births for ocular coloboma and 0.2–0.8 per 10,000 for eyelid coloboma. Exact numbers are hard to pin down because mild cases may never be diagnosed. The Texas registry reported a clear rise in recorded birth prevalence over its 16-year study period, which may reflect better detection as well as real change.
Coloboma symptoms: what do people notice?
Coloboma symptoms depend on which structures are involved and how big the gap is. Some people have none.
| Sign or symptom | What it can point to |
|---|---|
| Keyhole, pear-shaped or off-centre pupil | Iris coloboma |
| Sensitivity to light and glare | Iris coloboma (the pupil cannot narrow normally) |
| Reduced vision, or vision that glasses cannot fully correct | Chorioretinal or optic nerve coloboma; high refractive error; amblyopia |
| A missing patch in the visual field | Chorioretinal coloboma |
| Notch in the eyelid, dry or sore eye | Eyelid coloboma exposing the cornea |
| Small eye (microphthalmia), involuntary eye movement (nystagmus), squint | Often seen with larger or bilateral colobomas |
| Sudden shadow, curtain, flashes or a shower of floaters | Retinal detachment: urgent |
Vision problems may not be obvious at birth, which is why a child with a visible iris coloboma should have a full eye examination. In children, the AAO stresses preventing amblyopia (lazy eye) with glasses or patching of the better eye.
Related problems in colobomatous eyes include cataract, glaucoma, short-sightedness, nystagmus and squint. A paediatric series of 335 eyes with chorioretinal coloboma found other eye anomalies in 87.2%, including iris coloboma (71%), microcornea (45.1%), nystagmus (41.5%) and squint (21.2%).
How is coloboma diagnosed?
Coloboma is diagnosed by an eye examination, and a full dilated examination is needed because the back of the eye cannot be judged from the pupil alone. Typical steps:
Examination of the eye and pupil
, including the eyelids and iris, to see the size and shape of any gap.
Vision, refraction and field tests
, to measure how well each eye sees, whether glasses are needed and whether there is a field defect.
Dilated retinal examination
, to look at the choroid, retina and optic nerve and see whether the gap reaches the optic disc or the macula (the centre of vision). The Eye journal's 2021 clinical review stresses that vision depends mainly on whether the optic disc and fovea are involved.
Imaging
, where needed. Ultrasound is usually the first scan for the eye in children; CT or MRI is added when the doctor wants to look at the eye socket or the brain.
General and genetic assessment
, particularly for children with both eyes affected or other signs (heart, hearing, growth or facial differences), because CHARGE and other syndromes need a paediatrician or geneticist. Genetic testing and counselling can help families understand recurrence risk.
Coloboma on a scan (radiology)
On CT or MRI, a posterior coloboma shows as a focal gap in the back wall of the globe, often with a small eye and sometimes a fluid-filled cyst behind it. Iris colobomas are usually not visible on these scans, because they are seen directly. Radiopaedia also notes that scans help tell coloboma from morning glory disc anomaly, which can look similar and is linked with brain and skull-base differences. Imaging does not replace an eye examination; it adds to it.
Coloboma treatment: what can be done?
There is no treatment that closes a coloboma, and no cure. Treatment aims to protect vision, treat complications and improve comfort or appearance. The AAO and the clinical literature list these options, depending on the type.
| Problem | Typical approach |
|---|---|
| Blurred vision, refractive error | Glasses or contact lenses, started early in children |
| Amblyopia (lazy eye) | Patching or special glasses for the better eye, to train the weaker one |
| Iris coloboma: glare, light sensitivity or appearance | Coloured or prosthetic-iris contact lenses; surgery is an option in selected cases |
| Chorioretinal coloboma: risk of retinal detachment | Regular dilated checks; in some eyes, laser (retinopexy) to the edge of the gap to strengthen the retina; surgery if a detachment occurs |
| Cataract | Cataract surgery, which can be harder in small eyes with firm lenses |
| Eyelid coloboma | Lubricating drops and ointment to protect the cornea, then surgical repair; the method depends on the size of the defect |
| Low vision | Low-vision aids, training and support |
Coloboma of the iris: treatment options
An iris coloboma often needs no medical treatment, because it mainly affects appearance and glare rather than sight. Coloured, "artificial iris" contact lenses can make the pupil look round and reduce glare; they are fitted individually. Surgical options exist for selected eyes but are a specialist decision, since the retina and optic nerve behind the iris also need assessing first.
Retinal detachment: the main sight-threatening risk
When the retina or choroid is involved, the risk of retinal detachment is higher than average. EyeWiki puts the risk with posterior colobomas at 23–42%. In a series of 198 children (335 eyes), 17.6% had a retinal detachment overall, and the detachment rate was 2.9% in eyes that had preventive laser compared with 24.1% in eyes left untreated. This was an observational study with short follow-up, not a trial, and the Eye review adds that in most eyes the optic disc lies inside the gap, which can make complete laser treatment hard to do safely. Whether laser is advised is an individual decision for a retina specialist. Modern surgery for coloboma-related detachment gives consistently good results, according to the same review, but these operations can be complex.
Eyelid coloboma
Eyelid colobomas are most often found at the junction of the inner and middle third of the upper lid. The priority is to protect the cornea from drying. StatPearls explains that small defects, up to about a quarter of the lid, can often be closed directly, while larger ones need more extensive reconstruction.
Care with us: retinal and cataract assessment for people with coloboma-related eye problems is led by Doç. Dr. Muhammet Derda Özer (retina, cataract, cornea) and Op. Dr. Aysan Bayram (retinal disease, cataract), and eyelid surgery questions are handled by Prof. Dr. Ahmet Satıcı (eyelid and oculoplastic surgery). Send your reports and scans first, and the right surgeon will tell you whether treatment in Istanbul could help.
When to see a doctor about a coloboma
Seek same-day eye care if you have a coloboma and notice:
- a sudden shadow, curtain or veil across your vision
- new flashes of light or a sudden shower of floaters
- a sudden drop in vision in either eye
- a red, painful eye, especially if the eyelid does not close fully
Book a routine appointment if:
- your child has a keyhole or irregular pupil, or you notice a notch in the eyelid from birth
- a baby or child seems not to follow objects, squints, or holds things very close
- you have been told you have a coloboma and have not had a recent dilated retinal examination
- glare is making daily life or driving difficult
- you are planning cataract or other eye surgery and have a coloboma, because it changes how surgery is planned
If you already have a diagnosis and want a second opinion, you can send your scans before you travel.
Frequently asked questions
A coloboma is a gap in the eye that has been present since birth, where part of the normal tissue is missing. It can involve the iris, retina, choroid, optic nerve, lens or eyelid, and the effect on vision ranges from none to severe.
The main types are iris, chorioretinal (retina and choroid), optic nerve, lens and eyelid coloboma. An iris coloboma gives a keyhole-shaped pupil; a chorioretinal or optic nerve coloboma is at the back of the eye and often cannot be seen from the outside.
It is caused by incomplete closure of the embryonic fissure, the seam of the developing eye, in early pregnancy. Genes are involved (more than 40 are linked to it), it can be part of syndromes such as CHARGE, and most cases happen without a family history. Often the exact cause is not found.
Rare. MedlinePlus gives about 1 in 10,000 people, and published estimates for ocular coloboma range from 0.5 to 2.2 per 10,000 live births.
A keyhole pupil, sensitivity to light and glare, reduced vision, a missing area in the visual field, and, with eyelid coloboma, a notch in the lid and a dry eye. Some people have no symptoms.
Coloboma is a medical condition, not a label that applies to everyone who has it. Some people have normal vision and are barely affected, while others have low vision, field loss or light sensitivity that affects daily life. What matters is how much your vision and daily activities are affected, and low-vision services can help when they are.
The gap cannot be closed, so there is no cure. But glasses, lenses, treatment for lazy eye, laser or surgery for the retina, cataract surgery, eyelid repair and low-vision support can manage most of its effects.
It can increase the risk, particularly when the retina or choroid is involved. Published figures range from about 17% to 42%, depending on the study and the type of coloboma. Preventive laser may lower the risk in selected eyes. Regular dilated checks matter, and a sudden shadow or flashes need urgent care.
On CT or MRI, a posterior coloboma appears as a gap in the back wall of the eye, often in a small eye, sometimes with a cyst behind it. Ultrasound is often the first scan in children. Iris colobomas are visible on examination and generally do not need imaging.
Yes. Coloboma is also described in dogs: it is one of the two main lesions of collie eye anomaly, an inherited disorder widespread in herding breeds such as rough collies, Shetland sheepdogs and border collies. We care for people, not animals, so if you think your dog is affected, ask a veterinary ophthalmologist.
When people search for "coloboma ear", they usually mean the eye condition together with ear differences. Ear abnormalities are one of the features of CHARGE syndrome, which also includes coloboma of the eye, so an eye coloboma with ear differences is a reason to ask for a general and genetic assessment. Any notch or gap in the ear itself is a question for an ENT doctor or clinical geneticist rather than an eye surgeon.
Eye colour and coloboma are separate matters. Colour depends on pigment in the iris, while coloboma is a structural gap, and a colour chart cannot predict or exclude it. If you are curious about colour inheritance, try our Eye colour chart & inheritance calculator.
Sources for the facts on this page
- American Academy of Ophthalmology. What Is Coloboma? https://www.aao.org/eye-health/diseases/what-is-coloboma
- EyeWiki (AAO). Coloboma. https://eyewiki.org/Coloboma
- MedlinePlus Genetics (NIH). Coloboma. https://medlineplus.gov/genetics/condition/coloboma/
- EyeWiki (AAO). CHARGE Syndrome. https://eyewiki.org/CHARGE_Syndrome
- Vegunta S, Patel BC. Optic Nerve Coloboma. StatPearls, NCBI Bookshelf, updated 2023. https://pubmed.ncbi.nlm.nih.gov/30422472/
- Lingam G, Sen AC, Lingam V, Bhende M, Padhi TR, Xinyi S. Ocular coloboma: a comprehensive review for the clinician. Eye 2021;35(8):2086–2109. https://pubmed.ncbi.nlm.nih.gov/33746210/
- Uhumwangho OM, Jalali S. Chorioretinal coloboma in a paediatric population. Eye 2014;28(6):728–733. https://pubmed.ncbi.nlm.nih.gov/24675580/
- Mitchell DL et al. Epidemiology of coloboma: prevalence and patterns in Texas, 1999–2014. Birth Defects Research 2024;116(11):e2413. https://pubmed.ncbi.nlm.nih.gov/39530497/
- Radiopaedia. Ocular coloboma. https://radiopaedia.org/articles/ocular-coloboma
- Gerrie SK et al. Pediatric orbital lesions: ocular pathologies. Pediatric Radiology 2024;54(6):876–896. https://pubmed.ncbi.nlm.nih.gov/38321238/
- Fredholm M et al. Discrepancy in compliance between the clinical and genetic diagnosis of choroidal hypoplasia in Danish Rough Collies and Shetland Sheepdogs (collie eye anomaly). Animal Genetics 2016;47(2):250–252. https://pubmed.ncbi.nlm.nih.gov/26732749/
- Grosås S et al. Compliance between clinical and genetic diagnosis of choroidal hypoplasia in 103 Norwegian Border Collie puppies. Veterinary Ophthalmology 2018;21(4):371–375. https://pubmed.ncbi.nlm.nih.gov/29111596/
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