This underdeveloped tissue is normally in the lower part of the eye and it can be small or large in size. A coloboma occurs in about 1 in 10,000 births and by the eighth week of pregnancy.
Coloboma can affect one eye (unilateral) or both eyes (bilateral) and it can affect different parts of the eye. As coloboma forms during the initial development of the eye, it is present from birth and into adulthood.
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Most cases of coloboma appear without any previous family history, although in some families coloboma can be inherited, or could be caused by environmental factors such as certain drugs or infections during pregnancy.
The effect that coloboma has on vision depends on which structures of the eye are involved and how much tissue is missing.
Coloboma can affect your iris, the tissue that gives you your eye colour. Your pupil may look oval if the coloboma is partial, but if more of your lower iris is missing, your pupil will look more keyhole shaped. Both children and adults with only iris coloboma will probably have fairly good vision. However, iris coloboma is likely to cause light sensitivity (also called photophobia) in bright conditions. Light sensitivity and glare can cause discomfort and affect the quality of vision.
If the lens of the eye is affected by coloboma, vision is affected because of the change in lens shape caused by a notch or dent. There may also be some degree of cataract in the affected eye, which means the lens is cloudy instead of being clear. This cloudiness can cause symptoms such as blurred or misty vision, colours appearing dull and glare in your vision.
At the back of your eye, the retina (the light-sensitive layer) and the choroid (the layer of tissue and blood vessels behind the retina) can be affected by coloboma. This is known as a chorioretinal coloboma. An optic disc coloboma is where the optic nerve (which carries information from the eye to the brain) is affected by coloboma at the point where it leaves the back of your eye, an area known as the optic disc.
Someone with chorioretinal coloboma may not be aware of any visual symptoms. However, the more retinal tissue that is missing, the more their sight is likely to be affected, usually in the upper region of their field of vision. If the chorioretinal coloboma is large or there is optic disc coloboma, they are likely to have poor central vision. This will make activities such as reading, writing and watching television more difficult. If both eyes are affected by optic disc coloboma, they may also have nystagmus, meaning that their eyes move constantly and uncontrollably.
Sometimes, coloboma can increase the risk of other eye conditions, including:
Many children and adults with iris coloboma will require no treatment. However, some have a special contact lens fitted that covers the keyhole-shaped pupil and makes it look round. This improves the cosmetic appearance of the eye as well as reducing light sensitivity. For some people, surgery is an option, where the gap in the iris is sewn together to correct the pupil shape and reduce light sensitivity.
For other types of coloboma inside the eye, there is no treatment at present. However, other eye health problems that are associated with coloboma, such as glaucoma, retinal detachment, choroidal neovascularisation and cataract can be treated. It’s important for people with coloboma to have regular eye examinations with their optometrist, who will be able to check for any changes to their eye health. An optometrist will give advice on how often an eye examination is necessary. A person with coloboma who experiences any new symptoms or concerns should have their eyes examined straight away.
Although glasses and contact lenses are unable to improve any sight problems that are caused by coloboma, it’s important for children to have any focusing problems corrected to allow their sight to develop as fully as possible. Tinted glasses, sun hats or sun blinds in cars can help to relieve light sensitivity. Your optometrist (also known as your optician) will be able to offer further advice about this.
It’s completely natural to be concerned if you or your child has coloboma and normal to find yourself worrying about what it means now and in the future. We’re here to support you every step of the way, and to answer any questions you may have – just get in touch with our Sight Loss Advice Service.
You or your child may have normal vision or there may be some degree of sight loss. For a child, it’s difficult to predict to what extent their vision will be affected by coloboma in the long term. It's therefore important for them to attend their hospital eye clinic appointments and eye examinations to ensure they have the greatest chance of developing the best vision they can. It’s also important for adults to have regular eye examinations too.
For children who have sight loss as a result of their coloboma, having the right support at an early age can make a big difference. Your local authority should have at least one qualified teacher of visually impaired children (QTVI) to work with you and your child both at home and at school. QTVIs are qualified teachers who can provide support with development, play, learning and education. At an early stage, ask your local authority to put you in contact with a QTVI. If you have difficulty getting help, or need the details of the specialist teacher in your area, contact our Helpline.