University of Edinburgh
 

Medical Information on Aniridia

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 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

Due to staffing limitations we are not able to offer telephone or email advice to parents of children.

Medical Information on Aniridia

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 Aniridia?

Very rarely when a baby is growing in the womb not all of the parts of the eye grow. If the iris fails to grow then this is known as Aniridia. In some children only some parts of the iris fail to grow and the condition is called 'partial' Aniridia.

What is the cause of Aniridia?

The condition may run in families. A child can inherit Aniridia from a parent who also has the condition. Rarely it may occur for the first time in a family as a result of marrying a cousin or a more distant relative. About one third of cases of Aniridia occur by chance.

There is no evidence that Aniridia is caused by any prescription or recreational drugs or chemicals in the environment.

How is the diagnosis made?

Aniridia can be diagnosed during an examination by an ophthalmologist. Using a special piece of equipment called a slit lamp the ophthalmologist can see that parts of the iris are missing.

How does Aniridia affect the way a child sees?

Most young children will feel their vision to be 'normal' as they have never known anything else but their own visual world. At first they assume that everyone else has vision the same as their own. They do not realise that other people see things differently.

Aniridia can affect vision in different ways depending on the level to which the iris is affected and if there are other problems with the eyes. Both eyes are usually affected but one eye may be less affected than the other.

If a large part of the iris is missing then the sharpness of vision may be reduced so as the child may not see so clearly. This is because the normal iris and pupil reduce the amount of light entering the eye and help the lens to focus light to the back of the eye (retina). Without an iris too much light gets into the eye. This may cause glare and dazzle especially on sunny days.

Without an iris the light will not focus sharply onto the back of the eye. This causes blurred vision. Usually children with Aniridia can develop fast to-and-fro shaking movements of the eyes called Nystagmus. This 'camera shake' can also reduce sharpness of vision. Vision can often be improved by wearing spectacles that focus the light more sharply on to the back of the eye. Adding a tint to the lenses can reduce glare and dazzle.

Other parts of the eye can be affected in children with Aniridia

The pressure inside the eye can be higher than normal. The high pressure may damage the wires that join the eye to the brain (the optic nerve). This is called Glaucoma. In later life this can lead to poor vision. The pressure usually reduces with drops or an operation (Trabeculectomy). This prevents further damage to the optic nerve.

The cornea (clear window at the front of the eye) is the other part of the eye that can be affected. Later in childhood the skin on the surface of the cornea can begin to fail. This can make the surface of the cornea bumpy and irregular. This can make the eye uncomfortable and more photophobic. It can also lead to infection on the surface of the eye and scarring. This means that vision can become worse later in childhood. Lubricating and antibiotic drops can help make the eye more comfortable. Sometimes an operation can help to improve the surface of the eye and make vision better. The aim of an operation would be to replace the hazy cornea with a new clear one (corneal graft operation). Sometimes it is also necessary to replace ‘stem cells’ at the edge of the cornea. These help keep the skin on the surface of the cornea healthy.

The lens in children with Aniridia can become less clear in time.  When a lens becomes less clear this is known as a Cataract.  The cataract can be removed and replaced with a clear plastic one. This operation can improve vision.

An eye with Aniridia can sometimes have fewer wires joining it to the brain. This is known as Optic Nerve Hypoplasia. This can lead to poor vision.

A child with Aniridia needs regular check ups with an eye doctor to identify any of these conditions and to treat them if they arise.

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Are any other conditions associated with Aniridia?

About one third of cases of Aniridia occur by chance. These children have a 1 in 4 chance of developing a tumour of the kidney. In most cases a special blood test can tell which children are most at risk. The children most at risk need regular examinations of the kidneys so that if a tumour does develop it can be treated promptly. Children with Aniridia that runs in families are not at risk of developing a tumour of the kidney.

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 make friends.

It is important that children are encouraged to wear their spectacles. This will help the child see more clearly and reduce glare and photophobia. It will also help the vision parts of the brain to grow and develop correctly.

Most children with Aniridia have few problems getting around. The way they act can give the impression that their vision is normal. It is important however to be aware of your child's special problems with 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, especially if they also use their LVA. If a child has been given a Low Visual Aid (LVA) then they should be encouraged to use it.

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.

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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