Visually Impairing Conditionsby Dr Andrew Blaikie for VI Scotland
Medical Information on Leber's Optic Neuropathy
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
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
Edinburgh EH8 8AQ
Telephone Number : 0131 651 6078
Fax Number : 0131 651 6502
Textphone : 0131 651 6067
Medical Information on Leber's Optic Neuropathy
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 and all the bits that join them up need to be present and working for us to see normally.
What is Optic Neuropathy?
The optic nerve is the collection of all the 'communication' wires (over one million) joining the eye to the brain. If damage occurs to the retina or optic nerve then some of the wires in the optic nerve will wear out and disappear. This kind of condition is known as an optic neuropathy. By looking into the eye with a special instrument all these wires can be seen 'end on' as they exit the eye and pass to the brain. This is the 'head' of the optic nerve. If none of the wires are damaged then the 'head' of the optic nerve looks yellow and pink. If many wires are missing then the optic nerve looks pale and white. This is the common appearance in optic neuropathy conditions and is usually associated with visual impairment. Leber's optic neuropathy is one of these conditions.
The cells of optic nerve needs energy to work
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. Each cell has thousands of small power generators. The power generators are called 'mitochondria'. Each cell needs the energy made by the mitochondria to work. If the energy supply stops then the cell stops working. In Leber's Optic Neuropathy the mitochondria in the optic nerve stop supplying energy, which leads to visual impairment.
Genes hold the 'plan' for the cells of the body to work correctly
The body has a 'built-in' plan to make sure all the parts of the body work correctly. This plan is written in our genes. Genes are a chemical alphabet held in every cell of the body. Each child's mitochondria have its own set of genes inherited from their mother.
What is the cause of Leber's Optic Neuropathy?
Very rarely an error occurs in the chemical alphabet (genes) that causes the mitochondria to not work correctly and stop supplying energy to the cells. The cells of the optic nerve are the communication wires (nerves) from the eye to the brain. If these stop working then the information transmitted from the eye to the brain stops and vision becomes impaired.
Who is affected by Leber's Optic Neuropathy?
The condition usually affects boys in their teenage years. The condition rarely affects girls.
How does Leber's Optic Neuropathy affect a child's vision?
At first a child might notice blurred or 'grey' patches in the outer parts of their vision. The blurring and 'greyness' may then spread to the central vision causing visual impairment. The time between first noticing visual disturbance and developing central visual loss may be between a few days and several months. Leber's Optic Neuropathy always affects both eyes. The visual impairment often affects one eye first then the other weeks to months later. As the visual acuity reduces appreciation of colour also becomes impaired. The visual impairment although at first very marked often improves over the following two to three years.
Sometimes children with optic neuropathy can develop fast to-and-fro movements of the eyes known as nystagmus. Squint can also develop.
Are there any other conditions associated with Leber's Optic Neuropathy?
Occasionally other nerves and muscles may be affected. This can lead to irregular beats of the heart and weakness of some groups of muscles. This is sometimes important if the child is to have a general anaesthetic.
What can be done to help?
If one eye is affected more than the other patching of the child's better eye can encourage the other eye to develop better vision.
Sometimes children with optic neuropathy find spectacles improve vision. Special low visual aids can also help improve the child's vision.
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 socialise.
Most children with Leber's Optic Neuropathy have few problems getting around. Their behaviour can therefore give the impression that their vision is normal. It is important however to recognise their particular limitations of 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.
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.
Even if a child has very poor vision many useful and practical things can be done to help.