Retinal Dystrophy

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
• How the condition is diagnosed
• The effects of the condition on the child's vision
• 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. It is not a means to access a 'second opinion' particularly in any medico-legal cases. 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

Due to staffing limitations we are not able to offer telephone or email advice to parents of children who are not notified with VI Scotland.

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.
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

Medical information document on Retinal Dystrophy

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 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. There are two types of photoreceptors named by their shape when looked at in fine detail. They are called 'rods' and 'cones'.

Rod and Cone Photoreceptors are good at seeing different things
Rods are good at 'seeing': things that move in the dark but only in black and white and in less detail.
Cones are good at seeing: things that are still in daylight in colour and in fine detail.

The covering of rod and cone photoreceptors at the back of the eye makes a thin film called the retina. The central bit of the retina is made up of cones. They help us see the central bit of vision that we use for reading, looking at photographs and recognising faces. The area of the retina around the central bit is made up of rods. The rods see the surrounding bits of vision and help us to walk around and not bump into things especially in the dark or twilight.

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 Retinal Dystrophy?
Retinal Dystrophy is the name given to a wide range of eye conditions. These eye conditions are all linked by a problem with the rod and cone photoreceptors. The photoreceptors either do not work from the day a child is born or else slowly stop working over a period of time. Dystrophy is a word for a condition which a child is born with. Some of these conditions do not only affect the eye but may also affect the rest of a child's body.

Most Retinal Dystrophies are caused by misprints in a child's genes. Genes are a chemical alphabet stored in the body. Genes contain the body's 'built-in' plan to make sure all the parts of the body work correctly. If a gene has a misprint in the chemical alphabet then a part of the body may not work correctly. Sometimes many parts of the body do not work correctly. A child with a Retinal Dystrophy has often been passed (inherited) a gene with a misprint in it from one or both parents. Sometimes by chance a new misprint occurs in the child’s genes and the parent's genes are normal. There are several different ways a child can 'inherit' a condition.

What are the names for some of the more common Retinal dystrophies? Leber's Amaurosis, Retinitis Pigmentosa, Cone Dystrophy and Usher's Syndrome are the names of some of the more common conditions where rod and cone photoreceptors do not work properly.

How is the diagnosis made?
Young children with Retinal Dystrophy may develop:

• Fast 'to and fro' movements of the eyes called Nystagmus

• 'Roving' eye movements where the eyes appear to slowly wander around not fixing and staying still on any objects

• 'Eye Poking' where the child touches their eyes with their fingers

Parents will often notice these signs. Sometimes parents also notice (by the way their child acts) that their child's vision is reduced. If they discuss their concerns with their Family Doctor an assessment can be arranged.

An eye doctor can check the way the eyes behave to bright lights. If the pupils of a child move slowly to a bright light then Retinal Dystrophy is more likely. Using a special instrument the eye doctor can look at the optic nerve and retina at the back of the eye. In children with Retinal Dystrophy sometimes these parts of the eye look different from normal.

There are also special tests that can be done to help the eye doctor decide what is wrong. These tests measure signals from the eyes when a child is shown a bright light. Sticky patches are placed around the eyes. The sticky patches are attached to wires that lead to a machine. The machine records the electrical signals made by the eyes. The record of the signals will help the doctors decide what the matter is. If the signals are weak or absent then Retinal Dystrophy is more likely. This test is called an Electroretinogram (ERG).

Some Retinal Dystrophies may present initially with symptoms that have nothing to do with vision. Conditions such as Batten's Disease may present with increasing difficulty handling objects, increasing clumsiness moving around, gradual change in mood and personality, decreased attention span, slurred speech and poor memory. It may be only later that a problem with vision is noticed. This is a very rare condition.

How does Retinal Dystrophy affect the way a child sees?
Retinal Dystrophies can affect different children in different ways. At first most young children will feel their vision to be 'normal'. They will assume that everyone else has vision the same as their own, as they have never known anything else but their own visual world. They do not realise that other people may see things differently.

Older children may notice that their vision is blurred around the edges and that their vision is especially poor in the twilight and dark. These children might mainly have a problem with their rod photoreceptors. Some other children will also notice that their central vision is blurred and that colours are not bright and obvious. These children will have a problem with their cone photoreceptors as well. Some other children may only see bright lights or the movement of large objects. Some children with Retinal photoreceptors can have very poor sight and unfortunately are able to see very little.

It is important to appreciate that other people will not realise, just by looking at your child that they may not see well. This is particularly important in twilight and the dark. Children with rod photoreceptors that do not work so well will have even poorer vision at these times of day. Crossing roads when going to and from school can be especially dangerous, as motorists will not appreciate that your child cannot see clearly.

Are there any other conditions associated with Retinal Dystrophies? Some children with Retinal Dystrophies only have visual impairment. Many other children may have other conditions such as:

• Poor Hearing
• Learning Difficulties
• Reduced Growth

The other associated conditions depend on what the cause of the Retinal Dystrophy is.

Is there any treatment for Retinal Dystrophy? There is currently no common and reliable way to stop the sight loss in Retinal Dystrophy. Recently there have been some new efforts to try and stop sight loss in patients with retinal dystrophies although these are still very much in the experimental stage. Many other things can be done to help children with this condition.

What can be done to help?
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 child's 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.

Bright light often causes discomfort and reduced vision (photophobia). A sunhat and sunglasses may help reduce symptoms of photophobia. Special lenses that get darker in brighter light (photochromic lenses) are also known to be useful. Reducing exposure to sunlight and especially ultraviolet light that is also in sunlight can help slow the normal ageing changes in a retina and will almost certainly be helpful in children with a retinal dystrophy.

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. Sometimes placing reading books on a slope, which tilts the print towards the child, will improve reading speed as well.