Eye Conditions

by Dr Andrew Blaikie for VI Scotland

Medical Information on Batten's Disease

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

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 Batten's Disease

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 Batten’s Disease?

The body is made up many different parts such as skin, bone, muscle, and the brain. All the different parts of the body are made up of ‘cells’. Cells are tiny factories making materials that the body needs to work and grow. Cells also break down and get rid of any material the body does not need. The material is broken down by chemicals called ‘enzymes.’ Although the cause of Batten’s disease is not fully understood it is most probably due to one or several enzymes that do not work correctly leading to a damaging build up of fat and protein in cells. The damage causes cells to switch off and die. The number of cells in the brain and eyes gradually becomes smaller and smaller leading to the symptoms of Batten’s disease.

What causes Batten’s disease?

There are many thousands of different enzymes. The body has a "built-in" plan to make sure all the different enzymes work correctly. This plan is written in our genes. Genes are a chemical alphabet held in every cell of the body. Every person has two copies of each gene. If both copies of a gene carry the wrong plan for the same enzyme then that enzyme will not work. A child with Batten’s disease has by chance inherited a copy of the same gene from each parent with the wrong plan for the same enzyme. This is called ‘recessive inheritance’. That enzyme does not work which leads to the build up of fat and proteins in cells of the eye and brain and the development of Batten’s disease. The chance of a second child from the same parents developing Batten’s disease is one in four. There is a one in two chance of a second child with the same parents carrying the gene with the wrong plan, but not being affected (this is like both parents who are also unaffected ‘carriers’ of the gene for Batten’s disease). There is a one in four chance that the child will not carry any faulty genes at all.

How does Batten’s disease affect a child?

The build up of fat and protein only affects eyes and brain. The changes in the brain can lead to many different kinds of symptoms many of which at first can be very mild. Not all children will develop all the symptoms. Children will also vary in how affected they are by each symptom.

Symptoms include:

• Increasing difficulty handling objects
• Increasing clumsiness moving around
• Gradual change in mood and personality
• Decreased attention span
• Slurred speech
• Poor memory
• Development of epilepsy
• Deterioration in vision

As the condition progresses the child becomes weak and develops poor resistance to infection. There are several different forms of Batten’s disease that are classified by the age at which the child develops the condition. The earlier a child presents the shorter is the life expectancy. Most children live until they are in their mid to late teens and sometimes into their twenties.

How does Batten’s disease affect a child’s vision?

Many children with Batten’s disease come to the attention of medical professionals because of increasingly blurred vision. The progression may be very slow which allows the child to adapt and at first cope well with the visual impairment.

How is Batten’s Disease diagnosed?

Initially the child may not be diagnosed with Batten’s Disease until other symptoms develop such as clumsiness and epilepsy. When new symptoms develop Batten’s disease may be considered and special tests performed to confirm the diagnosis. A blood test and piece of tissue may be taken and looked at under a microscope. The build up of fat and protein can be seen in the cells and the diagnosis confirmed.

What can be done to help?

Epilepsy can be treated with tablets. Physiotherapy and occupational therapy can help maintain mobility.

Making contact with a support group can help parents and other family members cope.