Visually Impairing Conditions
Medical Information on Colobomaby Dr Andrew Blaikie for VI Scotland
For whom is this information intended?
The information contained in this document is intended for use primarily by parents, other members of the family and older children with visual impairment. The information will also be of use to interested health professionals, carers and teachers.
The purpose of each information document
The purpose of the information is to explain:
- The way the eyes and brain normally work to make 'vision'
- The reason why vision may become impaired by a specific condition
- The cause of the condition
- The effects of the condition on the child's vision
- How the condition is diagnosed
- What can be done to help
This document is written with the minimum use of medical terms and jargon. It is impossible to avoid all medical terms but where we have used them we have attempted to explain them as clearly as we can. Although the information is intended to describe most aspects of the condition each child is different and there will always be exceptions to the rule. As far as we can determine these pages are true and accurate and have been written in good faith. Inevitably there will be some mistakes. We apologise for this.What this information is not for
This document is not a substitute for a consultation with a Health Professional and should not to be used as a means of diagnosing a condition.
We hope the information will help you
After reading the information we hope you will:
- Have a better understanding of the condition
- Know what tests and treatments are normally available
- Know when to seek professional advice
- Be able to discuss the condition in a more informed way
- Make the most of consultations with carers, teachers and health professionals
- Be reassured and more able to cope
These pages represent the consensus of opinion of many different people who include Parents of Visually Impaired Children, Visually Impaired Children themselves, Community Paediatricians, Ophthalmologists, Educationalists and Psychologists.
The main author and person responsible for their content is Dr Andrew Blaikie who is an Ophthalmology Research Fellow with Visual Impairment Scotland and a member of the Royal College of Ophthalmologists. We are very keen that parents and children feedback to VI Scotland about these information documents. If you have any questions or comments regarding the information please contact:
Visual Impairment Scotland
Scottish Sensory Centre
The University of Edinburgh
Edinburgh EH8 8AQ
Telephone Number : 0131 651 6078
Fax Number : 0131 651 6502
Textphone : 0131 651 6067
Medical Information on Coloboma
What we see is made in the brain from signals given to it by the eyes.
What we see is in fact made in the brain. The brain makes sight from signals given to it by the eyes.
What is the normal structure of the eye?
The eye is made of three parts.
- A light focussing bit at the front (cornea and lens).
- A light sensitive film at the back of the eye (retina).
- A large collection of communication wires to the brain (optic nerve).
A curved window called the cornea first focuses the light. The light then passes through a hole called the pupil. A circle of muscle called the iris surrounds the pupil. The iris is the coloured part of the eye. The light is then focused onto the back of the eye by a lens. Tiny light sensitive patches (photoreceptors) cover the back of the eye. These photoreceptors collect information about the visual world. The covering of photoreceptors at the back of the eye forms a thin film known as the retina. Each photoreceptor sends its signals down very fine wires to the brain. The wires joining each eye to the brain are called the optic nerves. The information then travels to many different special 'vision' parts of the brain. All parts of the brain and eye need to be present and working for us to see normally.
What is a coloboma?
Very rarely when a baby is growing in the womb not all of the parts of the eye grow fully. If a part of the eye does not grow then this is known as a coloboma. Coloboma is a Greek word. It means 'curtailed' or 'unfinished'. The parts that sometimes do not grow fully include the iris, lens, retina or optic nerve.
What is the cause of coloboma?
Most cases of coloboma occur by chance. No reason or cause for it happening can be identified. This is called 'sporadic'.
Sometimes the condition runs in families. This is called autosomal dominant inheritance. An ophthalmologist should examine all the close relatives of a child with coloboma. Sometimes mild types of coloboma can be found in a parent or brother or sister of an affected child. This may help the doctors say if coloboma is likely to occur again in the same family.
Very rarely it may occur for the first time in a family as a result of marrying a cousin or even a more distant relative. This is called recessive inheritance.
There is no evidence that the coloboma is caused by prescription or recreational drugs or chemicals in the environment.
This document mainly refers to children with coloboma affecting both eyes
Most children with coloboma in only one eye usually have good vision in the other. These children do not normally complain of reduced vision. When both eyes are affected the child is much more likely to have blurred vision. This document mainly talks about children who have coloboma in both eyes.
How might coloboma affect a child's vision?
Coloboma can affect vision in different ways depending on how affected the eyes are. If only a small part of the iris is missing then the child's vision may be normal. If a large part of the retina and optic nerve is missing then vision may be poor. A large part of the visual world may be missing (visual field loss) and the sharpness of vision may be reduced. A child like this may only see bright lights and large shapes from the affected eye.
Despite this, young children with large colobomas and visual impairment will at first feel their vision to be 'normal'. They have never known anything else but their own visual world. They will assume that everyone else has vision the same as their own. They will not realise that other people see things differently.
Fast to-and-fro movements of the eyes can develop. This is called Nystagmus. Sometimes a child with coloboma can also develop a squint. This is when the eyes do not look in the same direction. If you wish more information on any of these conditions please ask us.
Are there any other conditions associated with coloboma?
Most children with coloboma are otherwise normal. Rarely however other conditions, especially of the eye, may also occur. The same eye or the other eye may be unusually small. This is called microphthalmia. A hazy lens (cataract) or high pressure (glaucoma) may also affect an eye with coloboma. All these conditions may blur vision further.
Eyes affected by coloboma are often short-sighted (myopic). Spectacles can sometimes help children see more clearly and ensure the vision parts of the brain grow and develop.
Some children with coloboma can have problems with other parts of the body as well. There is a very rare condition where children with coloboma also have poor hearing, learning difficulties, slow growth and problems with their heart. The condition is called CHARGE Syndrome.
If you wish more information on any of these conditions please ask us.
How are Colobomas diagnosed?
Parents may notice that a part of the iris is missing. It may look like a 'key hole' or a 'cat's eye'. Parents may also notice, by the way their child acts, that vision may be impaired. Parents should ask their family doctor for an assessment. An eye doctor can then diagnose most colobomas during an examination at the eye clinic.
How can doctors help?
Wearing spectacles can often improve vision. If the vision is worse in one eye than the other sometimes patching the better eye will help to improve the vision in the other. If other eye conditions develop such as cataract or glaucoma they can usually be treated.
How can parents, family, friends and teachers make a difference?
There are no effective medicines or surgical treatments that will fix the missing bits of the eye that occur in coloboma. There are however lots of things that can be done to help children with coloboma see better.
We use our vision to get around, learn new things and to meet other people and make friends. It is important to consider what your child's particular problems with vision might be now and in the future.
If your child has been prescribed spectacles, contact lenses or a Low Visual Aid (LVA) it is important that they are encouraged to wear and use them. This will help your child see more clearly and ensure the vision parts of the brain grow and develop.
Problems at school may be due to some of the reading books being hard to see. This often means it takes longer and more effort to do the work. If the size of print is increased and letters and words spaced more widely most children will find schoolwork easier. Good bright lighting and crisp black print on a clean white background will also make things easier. Sometimes placing reading books on a slope, which tilts the print towards the child, will improve reading speed as well. When reading it can be helpful to read one line at a time through a 'letter box' placed over the page. Placing a piece of blue tack below the line they are reading, at the beginning of the next sentence, can help some children find their way back to the start of the next line more quickly.
It is also worth watching carefully to find out what the smallest toys are that a child can see and play with. Then try to only play with toys that are the same size or bigger. Placing one toy on a plain background will often help children see it more readily. Placing lots of toys of different size and colour close together on a patterned background can make them 'invisible' to many children with poor vision.
Recognising facial expressions can often be difficult. It is worth trying to find out at what distance facial expressions can be seen and responded to. Then always try to talk and smile from within this distance. This helps a child to learn what facial expressions mean and to copy them. If the child has visual field loss try to place objects in the part of the child's vision that is working.
Infants and young children need to learn about the world around them. Home visiting teachers, physiotherapists and occupational and speech therapists may all add to the child's care and education. It is important to continue the programmes that they recommend. If the child is involved in family activities vision can improve and new skills can develop.
Even if a child has very poor vision many useful and practical things can be done to improve the ability of the child to get around, interact with other children and learn. Have a look at the advice section and the parents forum on the VI Scotland website.