University of Edinburgh
 

Medical Information on Neurofibromatosis

by Dr Andrew Blaikie for VI Scotland

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.

What this information is not for?

This document is not a substitute for a consultation with a Health Professional and should not be used as a means of diagnosing a condition.

We hope the information will help you to:

  • 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

Due to staffing limitations we are not able to offer telephone or email advice to parents of children.

Medical Information on Neurofibromatosis

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 optic nerves join about half way between the eye and brain, and then split up again. The join is called the optic chiasm. At the join, signals from the 'nose' side of each eye's visual world swap sides and continue travelling along the opposite side from where they started. The two optic nerves then join on to the brain. The brain is split into two halves, right and left. This means all the signals from the visual world on the child's right hand side are now travelling in the left side of the brain. It also means that all the signals from the visual world on the child's left hand side are now travelling in the right half of the brain.

The information then travels to the many different special 'vision' parts of the brain. The main bit of the brain that works vision is at the back of the head. It is called the occipital lobe. The joined up path that signals travel down from retina to optic nerve then optic chiasm then occipital lobe is called the visual pathway. There are two sides to the visual pathways, one on the right side of the brain and another on the left. All parts of both visual pathways need to be present and working for us to see normally.

What is Neurofibromatosis?

This is not one condition but two. The two conditions have in common:

  • typical marks on the skin; and
  • an increased risk of developing tumours.

Otherwise the two conditions are very different from each other. The more common form of Neurofibromatosis is called NF1 or von Recklinghausen's disease or peripheral Neurofibromatosis. The other type of Neurofibromatosis occurs ten times less often and is called NF2 or central Neurofibromatosis.

What causes Neurofibromatosis?

Neurofibromatosis develops when a misprint occurs in a certain gene of a child. Genes are a chemical alphabet stored in the body. Genes contain the body's 'built-in' plan to make sure all the parts of the body work correctly. If a gene has a misprint in the chemical alphabet then a part of the body may not work correctly. A child with neurofibromatosis has often been passed (inherited) a gene with a misprint in it from one parent. The gene causes neurofibromatosis. This is called autosomal dominant inheritance. Sometimes, by chance, a new misprint occurs in the gene that causes neurofibromatosis. Both this child's parents will have normal genes with no misprints. NF1 and NF2 are both autosomal dominant genetic conditions. They are however caused by two different genes developing misprints.

Why do children with Neurofibromatosis develop visual impairment?

There are a number of different reasons why vision might become impaired in this condition. In NF1 the main reasons are:

  • Optic nerve or chiasm glioma; and
  • Glaucoma

In NF2 the main cause of visual impairment include:

  • Optic nerve or chiasm meningioma; and
  • Cataract

What is glioma?

A glioma is a benign tumour of nerve tissue. A tumour is a condition where a part of the body grows more than it would normally. Benign means that bits of the tumour will not normally break off and spread to other parts of the body. It may, with time however grow and get bigger. The optic nerve and chiasm are made of nerve tissue and may develop a glioma. Most children present with this condition around nine years of age. Some may present much earlier, before they even start school. It usually only affects one optic nerve but in children with NF1 both may become affected. Growth of the glioma stops signals being transferred from the eye to brain. This may lead to visual impairment.

What is glaucoma?

Eyes keep their shape by being pumped up with water. It is a bit like a football being pumped up and inflated with air. You can feel the 'pressure' in your own eyes by gently feeling them through your closed eyelids. The amount of pressure depends on the flow of water in and out of the eye. The flow of water out of the eye may become blocked in NF1. This leads to high pressure that can cause damage to the optic nerve. Glaucoma is when the optic nerve is damaged by high pressure in the eye. This may lead to visual impairment. Drops and an operation called a trabeculectomy can often help to reduce the pressure.

What is meningioma?

A protective layer covers nerves. This covering is called the meninges. Children with NF2 are at risk of developing a benign tumour of the meninges. This is called a meningioma. The nerve of hearing is most commonly affected in children with NF2. This may lead to hearing difficulties. The optic nerve and chiasm may also become affected. As the meningioma grows it may press and damages these structures. This stops transfer of signals from the eye to brain and may also lead to visual impairment.

What is cataract?

Cataract is when the normally clear lens of the eye becomes hazy. If the lens is not clear then not all the light can get into the eye. This may lead to blurred vision. Most children with NF2 do not develop cataracts however a small number may. If the cataracts become very hazy, with poor vision they can be removed by an operation.

How is the diagnosis of Neurofibromatosis made?

Parents may notice that one of their child's eyes is sticking out further than the other (proptosis) or that their child is squinting. This may be due to a slowly growing tumour. Parents may also suspect, by the way their child acts, that their child's vision is impaired. Older children may sometimes complain that their vision is blurred or their eye is painful. If parents discuss their concerns with their Family Doctor an assessment can be arranged.

A school nurse or optometrist may also note blurred vision during a screening examination. They can organise an examination at the eye clinic.

At the eye clinic an eye doctor and orthoptists can assess the child's eyes and vision. If Neurofibromatosis is suspected other tests can be done. A head scan often helps to confirm the diagnosis.

What can be done to treat Glioma or Meningioma?

Many children with glioma or meningioma do not need any treatment. This is because these tumours grow so slowly that they do not cause any further problems. Regular checks are still needed at the clinic though. Scans can help to see if the tumour is getting any bigger. If the tumour is getting bigger and causing new problems then treatment may help. Three different kinds of treatment may help: Surgery, radiotherapy or chemotherapy.

  • Surgery: A surgeon might try to remove a tumour by an operation.
  • Radiotherapy: Often X-ray treatment is recommended. This is called Radiotherapy. X-rays are normally used to take pictures of patient's lungs and broken bones. When concentrated and focussed on to a tumour they can help slow down and stop its growth.
  • Chemotherapy: Sometimes drugs injected into a child's veins are also recommended. This is called chemotherapy.

Any decision on treatment is discussed fully with the child and their parents. All treatments can have side effects. The benefit to the child must always be weighed against any possible damaging side effects of the treatment.

How can parents, family, friends and teachers make a difference?

We use our vision to get around, learn new things and to meet other people and make friends. It is important to be aware of your child's own special problems with vision.

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 most children will find schoolwork easier. If a Low Visual Aid (LVA) or spectacles have been prescribed then try to encourage their use. This will help the child see more clearly. It will also help the vision parts of the brain to grow and develop.

It is 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.

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.

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.

Who wrote these documents?

These pages are the consensus of opinion of many different people. They 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 was an Ophthalmology Research Fellow with Visual Impairment Scotland and is a member of the Royal College of Ophthalmologists.

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