University of Edinburgh
 

Cerebral Palsy and Visual Impairment in Children: Experience of Collaborative Practice in Scotland

Chapter 1: Introduction by Andrew Blaikie

Introduction to Cerebral Palsy and Visual Impairment

How common is cerebral palsy?

For every 1000 new births in Scotland it is thought that about 2 to 3 children will have cerebral palsy. This means that in Scotland, where there are about 1 million children under the age of 16 years, there are about 2000 to 3000 children with cerebral palsy.

What is cerebral palsy?

Cerebral palsy (CP) is a condition that affects both movement and sensation. It is caused by damage to different parts of the brain. The damage may occur before birth, at birth or in early childhood. Some children's movement might be mildly affected while others will be more severely affected. Often at birth it is not possible to identify which type of cerebral palsy the child will have; the movement difficulties will become more obvious as the child grows and develops. Depending on where the damage to the brain has happened, the child may have other associated impairments: epilepsy; visual impairment; hearing impairment; communication; eating and drinking; emotional/behavioural; cognitive.

There are three main types of cerebral palsy which describe the difficulty with the child's movement:

1. Spastic cerebral palsy

Children with this type may find their muscles becoming very stiff and weak, especially under effort. This can reduce the amount of movement they have and they can be fearful of the movement because they cannot balance easily.

2. Athetoid cerebral palsy

Children with this type of cerebral palsy often lose control of their posture and will make often continuous and unwanted movements that they cannot control.

3. Ataxic cerebral palsy

Children with this type of cerebral palsy have lack of balance and demonstrate jerky movements. This description of their movement includes how they would move a body part, e.g. when reaching for a toy, as well as movement of their whole body for the purpose of moving around their environment.

While movement is described as being mildly to severely affected, ability to participate in everyday life is affected by the combination of the movement impairment and the other associated impairments. Therefore the child may be described as having a mild movement impairment but have a severe impairment in taking part in everyday activities, eg: play, eating and drinking, dressing or communicating.

Did you know, up to 70% of children with cerebral palsy also have a visual impairment?

Nobody is too sure exactly how many children with cerebral palsy also have difficulties with vision. However research has shown that up to three-quarters of all children with cerebral palsy have some kind of visual impairment (Sonsken, Petrie & Drew, 1991).

The reason nobody is too sure of the exact figure is because the types of visual impairment that children with cerebral palsy have, vary so greatly. Because damage to the brain is usually the cause of visual impairment in children with cerebral palsy, there are many more kinds of visual difficulties that may develop. It is not simply visual acuity that may be reduced. Children with cerebral palsy may have:

  • reduced visual acuity;
  • visual field loss;
  • difficulty using their vision to move parts of their body or to move around;
  • difficulty recognising objects;
  • problems focusing for near objects;
  • short or long sightedness;
  • problems making accurate fast eye movements;
  • problems keeping fixation still on an object.

Visual impairment does not just mean having poor visual acuity (sharpness of vision). It is many more things. In children in whom the eye is the cause of visual impairment, usually only visual acuity is affected. This is more straightforward to measure and it is easier to say for sure whether the child is visually impaired or not. The visual difficulties seen in children with cerebral palsy are more complicated to assess and describe. For these reasons nobody is too sure how many children with cerebral palsy also have visual impairment. All these visual difficulties together are often called cerebral visual impairment or CVI for short.

How do we see?

What we see is in fact made in the brain 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 focusing 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 cerebral visual impairment?

Cerebral visual impairment (CVI) is a condition where some of the special vision parts of the brain and its connections are damaged. This causes visual impairment even though the eyes are normal. Often children with CVI actually have good visual acuity but cannot make sense of what they see. In most cases, once the damage has happened it does not get worse. As the child develops the visual difficulties may slowly improve along with improvement of motor skills.

How is the diagnosis of visual impairment made?

It is often difficult to tell if a child with cerebral palsy has problems seeing because of other problems with movement, communication or learning difficulties.

Sometimes it is the parents who notice, by the way their child acts, that vision is impaired. If they discuss this with their Family Doctor an assessment can be arranged. Doctors, teachers and other carers should always consider that a child with cerebral palsy might have some kind of visual impairment. If they suspect a child to have visual impairment an assessment should be organised. CVI can be diagnosed in a child who has:

  • visual difficulty;
  • damage to the vision parts of the brain;
  • but apparently normal eyes.

However it is important to bear in mind that the child with cerebral palsy may have CVI as well as an eye condition that affects acuity or control of eye movements. A head scan will usually confirm the damage to the brain to confirm a diagnosis of cerebral palsy, but not all children will have had such a test.

There are other special vision tests that can also 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). It is also uncommon for children with CP to have these tests done.

Often the best way to find out if a child has CVI is by asking questions or observing the child during everyday activities. An eye doctor (ophthalmologist) can find out from the parents and other professionals involved with the child what kind of problems he seems to be having. The doctor's questions are based on their knowledge of the visual difficulties that commonly occur in children with cerebral palsy and CVI and they should be followed up by observations made by all those involved with the child.

What kind of visual difficulties is a child with CP and CVI likely to have?

Most young children with cerebral palsy and CVI 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 of an impairment.

How does the brain make sense of what the eye sees?

The many different vision parts of the brain combine together to make two visual systems or streams; the dorsal stream and the ventral stream.

The dorsal stream helps the child move in space

This system helps people to get around safely and quickly. It also helps people pick objects up and avoid bumping into things and falling over. The visual system that tells the body how to move 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 (the upper part of the brain).

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

  • reach forward and grab a cup or handle;
  • use stairs without falling.

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.

The ventral stream helps a child recognise objects

The other system, called the ventral stream helps us to recognise faces, objects and places. Ventral describes the part of the brain where the system is (the lower part of the brain). 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 childrens 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.

Children with CVI can have difficulty focusing when looking at near objects

The focusing power of the eye needs to increase when looking at a close object. In children with CVI the focusing power can be reduced. It can also become tired more easily. This is the usual situation for most adults when they become 40 or 50 years old. When this happens many adults need reading glasses. Some children with CVI may also benefit from reading glasses for the same reason.

Children with CVI may have difficulty making fast eye movements

Fast eye movements are called saccades. We use saccade eye movements to quickly change the direction that our eyes are looking. This helps us look at something that has suddenly changed position. This is so the eyes can follow and fix accurately on a fast moving object. The eyes can then give clear signals to the brain to make clear vision. Fast eye movements are also important for reading. They help us to move our eyes quickly across the page of a reading book. Saccades are important in many other visual tasks.

Children with CVI may have difficulty making fast eye movements. These children may tend to make quick head turns when looking around a room or reading, rather than making fast eye movements.

By using a few tips described in the What can be done to help? section children with this difficulty may find reading a bit easier.

What is visual field loss?

Visual field is the medical word for the full area that we can see: our visual world. If an area of our visual world is blurred or missing with the rest clear, then visual field loss is present. It is due to damage to some of the special vision parts of the brain. The relationship between brain damage and visual field loss is the opposite to what you might think.

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.

What can be done to help?

There are no medicines or surgical treatments that will fix or improve brain damage. There are, however, lots of things that can be done to help children with cerebral palsy and CVI make the most of their vision.

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 childs particular problems with vision might be now, and in the future. If your child has been prescribed spectacles, contact lenses or a Low Vision 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.

Some children may also benefit from using a computer program while reading. The program only shows one word of a sentence at a time. The word is in the middle of the computer screen. This reduces the need for fast eye movements. It can increase reading speed and reduce tiredness. One program is called ACE READER. There are many others. A demonstration can be downloaded from www.acereader.com.

It is also worth watching carefully to find out what the smallest toys are that a child can see and play with. Then try only to 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 sizes and colours close together on a patterned background can make them invisible to many children with CVI.

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. There is a special part of the brain that helps children make sense of faces. Sometimes this part is also damaged. These children may have difficulty responding to smiling even if their vision is clear enough. If the child has visual field loss try to place objects in the part of the childs vision that is working.

Cerebral visual impairment commonly occurs in children who have difficulty controlling both head and eye movements. Careful positioning of the head to prevent it falling to the side or falling forward can help a lot. This might also involve careful positioning of the childs whole body which in turn will assist in gaining the best position of his head.

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 childs 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 move, interact with other children and learn.

Reference

Sonksen, P, Petrie, A, and Drew, K (1991) Promotion of Visual Development of Severely Visually Impaired Babies: Evaluation of a Developmentally Based Programme. Developmental Medicine and Child Neurology, 33 (320-335).