University of Edinburgh
 

Medical Information on North Carolina 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

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.

Medical Information on North Carolina 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. They help us see the central bit of vision that we use for reading, looking at photographs and recognising faces. This part of the retina is called the macula. 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.

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 North Carolina Macular Dystrophy?

The Macula is the central part of the retina. This part is best at seeing in colour and in fine detail. Amongst many other things it is used for reading and looking at photographs and faces. A dystrophy is the medical word used for a condition that a child is born with. North Carolina is the place in America where this condition was first found.

Putting all this together: North Carolina Macular Dystrophy is an eye condition that children are born with that affects the central part of the retina (the macula). This same condition is sometimes also known as 'Dominant Progressive Foveal Dystrophy of Lefler, Wadsworth and Sidbury'.

What is the cause of North Carolina Macular Dystrophy?

North Carolina Macular Dystrophy is caused by a misprint 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. A child with North Carolina Macular Dystrophy has often been passed (inherited) a gene with a misprint in it from one parent. This is called autosomal dominant inheritance. Sometimes by chance a new misprint occurs in the child's genes and the parent's genes are normal.

The gene misprinted in North Carolina Macular Dystrophy normally helps the macular part of the retina to work. When it is misprinted it does not work so well and the macula also does not work so well.

There is a 50/50 chance that children of a person with North Carolina Macular Dystrophy will also be affected by the condition.

How is the diagnosis made and how does it affect a child's vision?

North Carolina Macular Dystrophy can affect different children in different ways. Young children with North Carolina Macular Dystrophy may develop blurred vision from an early age. They may dislike bright light and try to avoid daylight and well-lit rooms. This is known as photophobia. Sometimes fast to-and-fro movements of the eyes may develop. This is called Nystagmus. Parents often notice these signs. Sometimes parents also notice (by the way their child acts) that their child's vision may be reduced. If parents discuss their concerns with their Family Doctor an assessment can be arranged.

Using a special torch an eye doctor can look at the macula at the back of the eye. In children with North Carolina Macular Dystrophy these parts of the eye can look different from usual.

North Carolina Macular Dystrophy can be split into three 'grades'. The grades are based on the way the macula looks on examintion.

Grade I: 'mild'

The macula has small yellow spots on it. These are known as 'drusen'. Fine black speckles are sometimes also seen. Most children with this grade have normal or very near to normal vision.

Grade II: 'moderate'

The yellow spots all join up to make a large slightly raised pale patch over the macula. Most children with this grade will need to use larger print to read. They will however have no problems getting around or recognising faces.

Grade III: 'severe'

The pale patch becomes even whiter and bigger. Scar tissue may grow at the edges and over the center. Children with this grade may need to use magnification aids to read and have difficulty recognising faces from a distance. They will be 'missing' a patch of vision right in the center. Despite this most children with this grade will however still manage to get around with no problems.

Usually once the age of 12 years is reached the condition is stable. It is unusual for the grade to change or the vision to get any worse after this age.

What can be done to help?

There are no medicines or surgical treatments that will fix or improve the macula. There are however lots of things that can be done to help children with North Carolina Macular Dystrophy see better.

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 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. It may also help improve photophobia.

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. Good bright lighting and crisp black print on a clean white background will also make things easier. Sometimes placing reading books on a slope, which tilts the print towards the child, will improve reading speed as well. 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.

It is also 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 more difficult to see.

Recognising facial expressions may 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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