University of Edinburgh
 

Medical Information on Macular Dystrophy

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 and 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.

Medical Information on Macular 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 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. 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. This is called the macula. The macula help us see the central bit of vision. This is the bit of the retina 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. This is often called the peripheral retina. The rods in the peripheral retina see the surrounding bits of vision. They help us to walk around and avoid bumping into things, especially in the dark.

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 Macular Dystrophy?

Macular Dystrophy is the name given to the way the central bit of the retina looks in many different kinds of eye conditions. It is not a diagnosis. It is the description of an appearance of the retina. Using a special instrument the eye doctor can look at the optic nerve and retina at the back of the eye. In children with certain eye conditions the central part of the retina (macula) looks different from usual. The macula may appear pale with small specks of black, brown or red. If an eye doctors sees this appearance they often call it Macular Dystrophy. Dystrophy is the name for a condition that a child is born with.

In what eye conditions may Macular Dystrophy be seen?

Macular dystrophy is not a diagnosis or a single eye condition. It is a sign seen at the back of the eye, in one of many different eye conditions. Most of these eye conditions are linked by a problem with photoreceptors and other parts of the retina. Parts of the retina either do not work from the day a child is born (stationary) or else slowly stop working during childhood (progressive). This usually leads to blurred vision, poor colour vision and a dislike for bright light (photophobia). Dystrophy is a word for a disease, which a child is born with.

The eye conditions fall into three main groups:

  • Eye conditions in which only the macula is affected. This includes eye conditions called Progressive Cone Dystrophy and Stargardt's Disease.
  • Eye conditions in which the macula is affected as well as all other parts of the retina. This includes eye conditions called Rod-Cone Dystrophy and Vitelliform Dystrophy.
  • Eye conditions that are only one part of a condition that affects the whole body. This includes conditions such as Batten's disease.

If you wish a VI Scotland information document on any of these conditions please ask us.

Why do some children have Macular Dystrophy?

There are many different causes of Macular Dystrophy. Sometimes nobody can say for sure what the cause is. When no cause can be identified this is called Idiopathic. Most dystrophies are caused by a misprint in the 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 Macular Dystrophy has often been passed (inherited) a gene with a misprint in it from one or both parents. Sometimes by chance a new mistake occurs in the child's genes and the parent's genes are normal. There are many different ways a child can 'inherit' a condition.

This is only a brief summary of the genetics of Macular Dystrophy. There are exceptions to these general rules. This is why it is important that families with a child affected by Macular Dystrophy receive counselling from a specialist in genetics.

How is the diagnosis made?

Poor vision can present in many different ways. Often parents notice (by the way their child acts) that their child's vision is reduced. Older children may actually complain of blurred vision. Sometimes poor vision is noted during screening programmes at nursery or school. If poor vision is suspected the Family Doctor can arrange an assessment.

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 a there is likely to be a condition of the retina or optic nerve. Using a special instrument the eye doctor can look at the optic nerve and retina at the back of the eye. The macula may appear pale with small specks of black, brown or red. If an eye doctors sees this appearance they often call it Macular Dystrophy.

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. This test is called an Electroretinogram (ERG). This is difficult to perform on a young child and is often not done.

How does macular dystrophy affect the way a child sees?

There are many different kinds of eye conditions that can give the appearance of a Macular Dystrophy. Each different eye condition can affect eyesight in different ways. In some conditions the child's vision can be almost normal. In other conditions vision can be very poor. Sometimes children with Macular Dystrophy can also have other conditions of their body, not just their eyes.

A child who is born with poor vision will often initially grow up and feel their vision to be 'normal'. At first they 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 see things differently.

Older children who develop problems with their vision will however slowly notice problems such as:

  • Blurred vision, especially in the central bit of vision
  • Dislike of bright light (photophobia)
  • Poor colour vision

Vision around the sides is usually fine. This means most children can run around without bumping into things. Riding a bike in a large open space may be possible. Changes in the height of the ground, especially at kerbs can be difficult to notice however. This may lead to a few falls. Ball games can often be too quick and difficult.

Is there any treatment for Macular Dystrophy?

There is no good way to treat inherited genetic eye conditions that cause Macular Dystrophy. Usually there is also no good way to stop the sight loss. But many things can be done to help visually impaired children.

What can be done to help?

We use our vision to get around, learn new things and to meet other people and make friends.

Most children with Macular Dystrophy give the impression that their vision is normal. It is important however to consider what your child's particular problems with vision might be.

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.

Wearing a hat with a broad brim can also help reduce problems from bright light.

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 words spaced out a bit more, many children will find schoolwork easier. Good bright lighting and crisp black print on a clean white background will also help. Sometimes placing reading books on a slope, which tilts the print towards the child, will improve reading speed as well.

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. 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. 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 some children with poor vision.

A child who chooses to use a head turn or to move the head to and fro to improve vision should not be made to stop doing this. They are trying to improve their vision and are often doing it without knowing it.

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.

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.

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