Medical Information on Visual Field Loss
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. It 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.
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 to the occipital lobe is called the visual pathway. There are two 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.
The visual field is the medical word for the full area of a child's visual world (what they see). Visual Field Loss may occur if damage occurs to any part of the visual pathway. The visual pathway that signals travel along includes the eye, optic nerve and the special 'vision' parts of the brain. The main part of the brain that deals with vision is called the occipital lobe. It is found at the back of the head. Damage to the visual pathway may cause blurring or even complete loss of bits of the visual world (visual field). In most cases, once the damage has happened it does not get worse. As the child grows the visual field loss may sometimes slowly improve.
What are the different causes of Visual Field Loss and how might they affect a child's visual world?
The different causes and types of visual field loss depend on the part of the visual pathway that is damaged.
Causes of damage to the Retina or Optic Nerve
There are many different causes of damage to the retina and optic nerve. Some of the more common causes include:
These conditions may cause patches of visual field loss. The macula is the central bit of the retina. This bit is for seeing in fine detail and in colour. It is used for things like reading, watching TV and recognising faces. If this bit of the retina gets damaged then the child is very likely to complain of blurred vision. If a bit of retina away from the centre is affected then the child may not notice the visual field loss at all.
If damage occurs at the optic chiasm a special type of visual field loss may occur. The child will lose the outside bits of the visual world on both sides. It is called a bi-temporal hemianopia. 'Bi' means both right and left sides. 'Temporal' means the outside bit of vision. 'Hemi' means half and 'anopia' means no vision. Damage to the chiasm may occur from small growing tumours. This is very rare in children.
Causes of damage to the brain
There are many different causes of damage to the visual pathway in 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. The reasons for damage to the brain while in the womb are often not known or well understood. Some cases might be due to the lining of the womb becoming infected. This type of damage can also be associated with early (premature) birth.
Damage can also occur around the time of birth. If the baby becomes 'tired' during birth, damage can sometimes occur to the brain. This might be due to poor blood supply to the baby or difficulty with breathing.
Most children even if they do have problems in the womb or during birth do not have any problems with vision or the brain.
There are many other causes of damage to the brain that can affect vision after a child is born such as:
- Infection (meningitis, encephalitis and infected intracranial aneurysms)
- Damage to the drainage of water from the brain (hydrocephalus)
- Serious head trauma
- Brain tumours
If a part of the right visual pathway in the brain is damaged the child may develop left visual field loss. If a part of the left visual pathway is damaged the child may develop right visual field loss. If the top part of the visual pathway is damaged the child may develop visual field loss in the bottom part of the visual field. If the top part of the visual pathway is damaged the child may develop visual field loss that affects the bottom of the visual field. The relationship between visual pathway damage and visual field loss is all opposite to what you might think.
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. If they discuss this 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 visual field loss.
An eye doctor can diagnose visual field loss during an examination. By also asking questions of the parents and teachers of the child, about the way the child acts, useful clues can be gained about where and what kind of visual field loss the child may have.
A head scan may help confirm where and what kind of damage has happened to the vision parts of the brain.
In some older children and in many adults it is possible to measure the visual field with a machine. This is called perimetry. Most children cannot do this test and it is rarely recommended.
There are no medicines or surgical treatments that will repair damage to the visual pathway. There are however lots of things that can be done to help improve vision in children with visual field loss.
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.
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 correctly.
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 word spaced out a bit more most children will find schoolwork easier.
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 find tilting their head one way and the book the other means they avoid reading in the part of their visual field that is blurred.
Some children may also benefit from using a computer program while reading. The program only shows one word of a sentence at a time. It 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 version of this program is called Ace Reader. A demonstration can be downloaded from www.acereader.com. All these 'tactics' can help to improve reading speed. Not all children will benefit from them however.
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. If the child has visual field loss try to place toys in the part of the child's vision that is working. 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
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.
Visual field loss may occur in children with Cerebral Palsy. 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. Some children with Cerebral Palsy may see poorly in the lower part of their visual world. Placing objects away from this blurred area can be helpful.
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.