A coloboma is a gap in part of the structures of the eye. This gap can be large or small and is normally in the bottom part of the eye.
A coloboma is caused when a baby's eyes do not develop properly during pregnancy. The eyes develop between the fourth and anything up to the fifteenth week of pregnancy, though development is usually completed around eight weeks. This condition occurs in about 1 in 10,000 births.
Coloboma can affect one eye (unilateral) or both eyes (bilateral). Coloboma can affect a number of different parts of the eye. A coloboma does not mean that there is a hole in the eye, but that certain structures or parts within the eye did not fully form.
A coloboma can affect the iris which is the coloured part at the front of the eye. It can affect the lens, the part of the eye which helps focus light onto the retina.
Coloboma can also affect the choroid which is a thin network of blood vessels which help to keep the retina healthy. Finally, it can affect the retina at the back of the eye. Very rarely coloboma can also affect the optic disc or the eyelid.
A coloboma forms whilst the baby grows in the womb. The eyes develop early during pregnancy and start off as little buds. Usually the eye folds in on itself as it develops which leaves a small gap called the foetal cleft.
The foetal cleft helps maintain the blood supply to the developing parts of the eye. In the final stage of eye development during pregnancy the cleft seals up from the back of the eye forwards and all the structures of the eye are formed. In an eye with coloboma this gap does not fully close and remains in some of the structures of the eye.
If the hospital staff suspect a child has a coloboma, which is normally first noticed by the possible keyhole-like shape of the pupil, then an ophthalmologist (eye doctor) will carry out a full eye examination.
The ophthalmologist would normally use an instrument called an ophthalmoscope to examine the inside of a child's eyes. The ophthalmoscope is held close to the eye but will not touch it. A baby may be given a general anaesthetic to allow the ophthalmologist to carry out a eye examination. This allows the doctor to look thoroughly at the baby's eye whilst he or she is still without causing any distress.
This kind of thorough eye examination at the hospital will help them to find out how much of the eye has been affected by the coloboma. It may be hard to tell how much a child's sight has been affected until they are older. This is because small children aren't able to communicate in words how good their vision is.
The hospital may also carry out other examinations to check on your child's general health
The affect coloboma has on vision depends a lot on which part of the eye is affected and how big the gap is. Normally the gap is at the bottom of the eye (where a 6 is on the face of a clock) and runs from the front to the back of the eye. Coloboma may affect only the front of the eye if most of the cleft has sealed up. It may affect the eye from the front to the centre and back if more of the cleft has failed to close.
Most commonly coloboma only affects the iris. Children with this type of coloboma often have fairly good vision. Their pupil may be shaped a bit like a keyhole. They may have some problems with and dislike bright lights because the iris, which usually limit the amount of light entering the eye by controlling the size of the pupil may not work properly. Too much light entering the eye can cause discomfort and distort the image created. Measures can be taken to help protect a child from sunlight such as tinted glasses, sun hats or sunblinds in cars.
If the coloboma goes further back into the eye then the child may have more visual problems, especially if the retina is involved. If this has happened then central vision may be affected. Central vision is used for detailed activities such as reading, writing and close work or play. If this is the case, specialist support services for children with a visual impairment will be involved.
Support services can help a child and his or her carers learn how to make the most of the vision the child has. Specialist services are mentioned at the end of this leaflet. They can provide information on development, play, education and many other issues.
Coloboma may affect one eye more than the other, so one eye may have better vision than the other.
Sometimes children with coloboma may have other problems and some 'syndromes' which include coloboma, such as CHARGE, a rare condition which stands for:
C - coloboma
H - heart defects
A - atresia of the choanae (problems with the nose passages)
R - retarded growth and developments
G - genital hypoplasia (undescended testicles)
E - ear abnormalities.
The hospital and medical staff will tell you if there are any other existing health issues and offer the relevant treatment and support services from a very early age.
Most cases of coloboma appear without any previous family history. In some families coloboma can be inherited. If a child is diagnosed with coloboma it is advisable for the child's parents to have an eye examination. This is because coloboma can be present without causing any visual problems. Therefore a parent might have coloboma but not know it. If an eye examination detected coloboma then a parent could explore inheritance patterns with the hospital or genetic counsellor.
The genetic factor responsible for most cases of coloboma has not yet been identified. Research is on-going to identify genes and any environmental factors that may cause coloboma.
If coloboma has occurred in your family and you would like to talk through the issues of genetics then you could ask your GP to refer you to the local clinical genetics department who could explore this with you.
There is no treatment for coloboma at present. A child with coloboma will receive specialist care at hospital during the early years to monitor the effect of the coloboma and their eye health. The frequency of these checks will depend on the child's needs. Children who have coloboma can be more at risk of glaucoma (increased eye pressure) and retinal detachment. There are treatments for both of these conditions which the hospital would explore with you.
If your child's eye health is stable and no further complications appear then they will usually attend an eye test every six months up to the age of seven years and then annually. These eye tests will usually take place with an optician or orthoptist.
Children with coloboma may need glasses. Glasses cannot correct the vision problems caused by the coloboma. However, glasses can correct short-sightedness or long-sightedness which can help to correct the parts of vision that haven't been affected by coloboma.
Sometimes cosmetic contact lenses may be considered at a later stage. These can help to make the pupil look round rather than keyhole shaped.
Prescription sunglasses due to the light-sensitivity may also be suggested, as may some low vision aids and equipment to help a child make the most of their sight.
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