Eye Conditions

Medical Information on Lissencephaly

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 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

Authors

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
Holyrood Road
Edinburgh EH8 8AQ

Telephone Number : 0131 651 6078
Fax Number : 0131 651 6502
Textphone : 0131 651 6067

Email : viscotland@ed.ac.uk
Website : www.viscotland.org.uk

Medical Information on Lissencephaly

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 Lissencephaly?

When a baby is growing in the womb not all parts of the brain may grow correctly. About one third of the way through pregnancy folds on the surface of the brain normally develop. These folds increase the brain’s ability to work once the child is born. In children with Lissencephaly the folds may not form at all. This is called agyria. Agyria means with no folds. Sometimes folds form but in reduced number and thicker than usual. This is called pachygyria. The word Lissencephaly is derived from the Greek "lissos" meaning smooth and "encephalos" meaning brain. The ‘vision’ parts of the brain may also lack folds and be smoother than usual. This may lead to visual impairment once the child is born.

How does this condition affect a child?

Different children can be affected in different ways and to different degrees. Some children can achieve speech and language skills appropriate for their age. Most children however suffer from profound learning difficulties and developmental delay. Many children develop epilepsy. Children may have difficulty swallowing and feeding. This can lead to water and food going into the lungs. This can lead to frequent chest infections. More information about this condition can be gained from the support group printed at the bottom of this information document.

Because vision is ‘made’ in the brain visual impairment is common. Visual impairment in children with Lissencephaly is called ‘Cerebral Visual Impairment’.

What is Cerebral Visual Impairment?

Cerebral Visual Impairment (CVI) is a condition where some of the special ‘vision’ parts of the brain are damaged and not working properly. This causes reduced vision, even though the eyes are normal. In most cases, once the damage has happened it does not get worse. As the child grows vision may slowly improve.

What are the causes of Cerebral Visual Impairment?

There are many different causes of damage to the ‘vision’ parts of the brain. The damage can also occur at different times in the child’s life. Often it is not known what the cause of the damage to the brain is. Most often damage occurs while the unborn child is still in the womb. This is the case for children with Lissencephaly.

How is the diagnosis made?

If a child is suspected to have visual impairment an assessment can be organised. Sometimes it is the parents who notice (by the way their child acts) that their child’s vision is impaired. Sometimes it is difficult to know if a child has CVI because of other problems with speech and language or learning difficulties. If parents discuss their concerns with their Family Doctor an assessment can be arranged. In most children damage to the brain may already have been diagnosed. The doctors looking after the child may then also suspect poor vision.

CVI can be diagnosed in a child who has:

1. Visual Impairment and
2. Damage to the ‘vision’ parts of the brain but
3. Normal eyes

A head scan will usually confirm that the vision parts of the brain have not developed normally.

There are other special tests that can be done. These tests measure signals from the ‘vision’ parts of the brain when a child is shown patterns on a screen. Sticky patches are placed on the back of the head. The sticky patches are attached to wires that lead to a machine. The machine records the electrical signals made by the brain. The record of the signals will help the doctors decide what the matter is. If the signals are reduced in size or slow then CVI is more likely. This test is called a Visual Evoked Potential (VEP). Sometimes this test can also give an idea of the child’s level of vision.

How does cerebral visual impairment affect the way a child sees?

Most young children with Cerebral Visual Impairment feel their vision to be ‘normal’ as they have never known anything else but their own visual world. At first they assume that everyone else has vision the same as their own and do not realise that other people see things differently.

Cerebral Visual Impairment can affect vision in many ways. All or only one of the special ‘vision’ parts of the brain can be damaged to different degrees. If there has been lots of damage to many parts of the brain the vision can be very poor. However the child may still see movement and bright lights. Complete blindness due to brain damage is rare.

If there has been only a small amount of damage in only one part of the brain the visual problem can be a lot less impairing.

Cerebral Visual Impairment can cause Visual Field Loss

If certain parts of the brain are damaged with other bits not affected there may be loss of only one half or quarter of the visual world. This is called visual field loss. Different patterns of visual field loss can occur.

The right side of the brain is responsible for seeing the left side of the visual world. The left side of the brain sees the right side of the visual world. If the right side of the brain is damaged the left side of the visual world may not be seen. In the same way the upper part of the back of the brain is responsible for seeing the lower part of the visual world. A child with damage in this area will not see the ground when looking straight ahead. The child may then tend to trip over things.

In Lissencephaly most parts of the brain are affected. This is likely to lead to blurred vision and visual field loss in all parts of the visual world.

Problems with getting around and recognising objects

The many different ‘vision’ parts of the brain combine together to make two visual ‘systems’.

1. The ‘dorsal stream’

One system helps the child to get around safely and quickly. It also helps the child pick objects up and avoid bumping into things and falling over. This visual system that tells the body how to get around is called the ‘dorsal stream’. It is called a ‘stream’ because it is a flow of information about the visual world from one place to another like water flowing in a stream. ‘Dorsal’ describes the part of the brain where the system is.

When the dorsal stream is damaged it is difficult to know precisely where things are in three dimensions. It can be difficult to:

• Use stairs without falling.
• Step onto pavements without tripping.
• Reach forward and grab a cup or handle.

Damage to the dorsal stream can also make it difficult to see a lot of different things at the same time. This means it can be difficult to find a toy on a patterned carpet or to see something that is pointed out in the distance amongst other things.

2. The ‘ventral stream’

The other system, called the ‘ventral stream’ helps us to recognise faces, objects and places. Damage to this system leads to problems:

• Recognising familiar faces.
• Knowing what common everyday objects are.
• Losing the way in places that should be well known to the child.

There are a number of other problems that can occur in children with CVI who still appear to have good vision. These include:

• Difficulty remembering things they have seen.
• Difficulty imagining ‘seeing’ things in their minds.
• Some children’s vision can become ‘tired’ more quickly than others. This means that their ability to see can vary from one time to another.
• Difficulty reading. This can be due to lots of different reasons.

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

There are no medicines or surgical treatments that will help CVI.

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.

Words in books or a computer screen may be being hard to see. This often means it takes longer and more effort to do read. If the size of print is increased most children will find reading easier.

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. If the child has visual field loss try to place objects in the part of the child’s vision that is working.

Parents can make a big difference. If spectacles have been prescribed they need to be worn while the child is awake and active.

In children with Lissencephaly both head movements and eye movements may be slow and difficult to control. Careful positioning of the head to prevent it falling to the side or falling forward can help a lot.

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. See the Advice section on the VI Scotland Website.

Parents of children with Lissencephaly often benefit from sharing experiences with other parents with similar children. It is recommended that parents contact a support organisation called the Lissencephaly Contact Group. They can be contacted at the address below:

c/o Contact a Family
209-211 City Road
London EC1V 1JN
Tel 020 7608 8700
Fax 020 7608 8701

e-mail: info@cafamily.org.uk