Aniridia

Aniridia means the iris, which is the coloured part of your eye, is missing or incomplete. Some children with aniridia may only have mild blurred vision and others may have quite a lot of sight loss.

What is aniridia?

Aniridia is a rare condition which means the iris, the coloured part of your eye, is missing or incomplete. Aniridia normally affects both eyes and it is a condition which babies are born with.

Your iris is a muscle which controls the size of the pupil to allow different amounts of light into your eye. The pupil is the dark hole in the middle of your iris. If your iris is incomplete or missing then your pupil will be very large. This means that your eye isn’t able to adjust to differing levels of light. Aniridia can cause poor vision and sensitivity to light.

In some rare cases aniridia is caused by other eye conditions or by trauma to the eye.

Sometimes aniridia can cause problems with other parts of your eye. How your sight is affected by aniridia depends on how badly your iris is affected and whether other parts of the eye developed normally before you were born.  

How the eye works

There are many different parts of the eye, all of which have an important role in making sure your vision is clear and in focus. Parts of your brain are also involved in your sight.

Your eye is shaped like a round ball. At the front of your eye is a clear tissue called the cornea, it allows light to enter the eye. Your cornea focuses light through your pupil which is a hole in the centre of your iris, the coloured part of your eye. Behind the iris is your lens, this also focuses the light coming through the cornea.  Both the cornea and the lens focus the light coming into your eye onto an area at the back of your eye called the retina.

When the light reaches the retina it converts the light into small electrical charges which are then sent through the optic nerve to the brain. Your brain is able to interpret these electrical signals into the images that you see. The eye and the brain together produce the images that we see. The communication between your eyes and brain is known as the visual system.

What causes aniridia?

Most cases of aniridia are inherited, which means the faulty gene which causes it is passed from parent to child. The gene which causes aniridia is the PAX6 gene. If this gene is faulty or missing, it stops the eye, and in particular the iris, developing fully when a baby is in the womb.

In some cases aniridia is not inherited but develops by chance.

Genetics of aniridia

What is a ‘faulty’ gene?

All genes come in pairs and you inherit one of each pair from your mother and one of each pair from your father. Your genes determine the many things which make you an individual such as hair or eye colour. There are a number of ways a genetic condition can be passed through genes from parents to children. These 'ways' are also known as classification of inheritance or inheritance patterns.

Aniridia is mainly passed on through the autosomal dominant inheritance pattern, but can sometimes be passed on through the recessive inheritance pattern in a very small number of cases.

Autosomal dominant inheritance pattern

It is important to remember when discussing inheritance that genes are inherited in pairs, one from your mother and one from your father.

A dominant condition is inherited from only one of your parents.  When the 'faulty' gene pairs up with the gene from your other parent, it is the dominant one and ‘switches on’ the condition.  When someone who carries the aniridia gene has a child with someone who does not carry the aniridia gene there is a 50% chance that the aniridia gene will be passed to a child. If a child does not inherit the aniridia gene they cannot pass it on to their children. The most common type of aniridia, called (AN)-1, is inherited through the autosomal dominant (AD) inheritance pattern.

For more information on genetic conditions, talk to your child’s eye specialist (ophthalmologist) about obtaining a referral to a genetic counsellor at the hospital and your GP about the genetic services in your area. The Genetic Alliance UK can also provide you with support and information and their contact details are at the end of this information.

Recessive inheritance patterns

Some rarer cases of aniridia are passed through a recessive inheritance pattern. For you to develop a recessively inherited type of aniridia you would need to inherit two faulty copies of a gene, one from each parent.

Since a parent carries one normal and one faulty copy they are termed carriers of the faulty gene. For parents, who don’t have aniridia themselves, the normal copy compensates for the presence of the single faulty copy. If you inherit both faulty copies of the gene, then you will develop aniridia.

Aniridia (AN)-2 with Miller Syndrome or aniridia (AN)-3 with Gillespie Syndrome has an autosomal recessive pattern of inheritance. When two people who carry a faulty PAX6 gene pass their faulty copy to one of their children, then that child will have this more unusual type of aniridia. 

For more information on genetics and how aniridia is passed through families you may want to speak to your GP about a referral to a Genetic Unit. You may also wish to contact the Genetic Alliance UK for more information.

How can Aniridia affect the eye and vision?

Some children with aniridia may only have mild blurred vision and others may have quite a lot of sight loss. Sight loss can really vary from child to child. Generally speaking, how much your child's vision is affected depends on what other parts of the eye may have been affected by aniridia and to what extent.

Other eye conditions can be linked with aniridia. These other eye conditions might be present at birth or develop later on when a child is a bit older. Your child's specialist will examine their eyes on a regular basis. How often the specialist will examine your child's eyes usually depends on how much vision your child has and what parts of their eye have been affected. These regular eye examinations can help to protect your child's useful vision and lets the specialist give any additional treatments that may be necessary.

Is there any treatment for aniridia?

Unfortunately there is no treatment to cure aniridia at the moment. There may be treatments available if you have or your child has other eye conditions as well as aniridia.

Your child's ophthalmologist will examine your child's eyes on a regular basis and will talk you through any possible treatment options.

What other eye conditions can be linked with aniridia?

The following eye conditions can be linked with aniridia. Your child's ophthalmologist will check their eyes thoroughly and let you know what is happening and discuss possible treatments with you.

Amblyopia: The visual pathway, that is how your eye and brain communicate with each other, goes on developing up until around the age of seven. During this period of development your eye needs to produce a clear image otherwise the visual system will not fully develop.

If one eye is sending poorly focused, unclear images to your brain, your brain will learn to “switch off” from these images in favour of those provided by your ‘stronger’ eye. This prevents your visual system from developing properly in your ‘weaker’ eye. This is known as amblyopia or lazy eye. Amblyopia may result in permanent visual loss. This can happen in children with aniridia that is much worse in one eye than the other because the image produced by the eye with the worst aniridia is not as clear as that from the better eye. Patching may help amblyopia.

Patching the stronger eye encourages your child to use their weaker eye which is known as occlusion therapy.

  • Your baby's ‘stronger’ eye may be patched for several hours a day in early childhood.
  • Patching aims to encourage your baby's visual system in the ‘weaker’ eye to develop.
  • If the consultant’s patching advice is strictly followed the better the chance of your baby developing the best vision possible in the weaker eye.
  • Sometimes drops can be put in the stronger eye to blur vision rather than wearing a patch or if wearing a patch isn't possible.

The orthoptist at hospital will be able to advise on the various ways to help your child to develop their vision as much as possible.

Corneal changes: The cornea is the clear outer layer covering the front of you eye. Normally it is smooth and as transparent as glass but it is also very strong.

Children with aniridia may have a number of problems which affect their corneas.

  • Aniridic Keratopathy: corneal clouding or scarring can develop during your child's early years.
  • Microcornea: underdeveloped or small cornea.
  • Dry eye: a problem with tear production. Dry eye causes the eyes to feel sore, gritty and may make them red.

Cataract: clouding of the normally transparent lens just behind the iris which can blur vision. Cataract can develop in 50-85% of children with aniridia. This would make your child's vision fuzzy.

Glaucoma can cause permanent damage to the optic nerve at the back of your eye due to the eye pressure being higher than normal. Glaucoma  develops in around 50% of children with aniridia and often develops as they get older in late childhood, adolescence or early adulthood. If you or your child have high eye pressure, your doctor may prescribe eye drops to lower it to a safe level to try to stop any more damage from happening.

Fovea Hypoplasia: The fovea is the central part of the retina at the back of the eye.  It is responsible for detailed vision which we use when reading, writing, or recognising someone's face across the road. Fovea hypoplasia can make it difficult for your child to use their detailed vision. Most children with aniridia have a degree of foveal hypoplasia but the severity varies from one child to another.

Nystagmus: an uncontrolled movement of your eyes, usually from side to side, but sometimes the eyes swing up and down or even in a circular movement. Most children with nystagmus have reduced vision as detailed vision is affected. Distance vision may be more difficult than near to vision. Nystagmus is very common in children with aniridia and how much it affects sight will vary from child to child.

Optic Nerve Hypoplasia: underdevelopment of the optic nerve, which around 10% of children with aniridia are born with. The optic nerve is like a bundle of wires which connects your eye to your brain. If your child's optic nerve is underdeveloped it may interfere with visual information being passed from their eye to their brain which can affect vision.

If amblyopia, aniridic keratopathy, cataracts or glaucoma develop or worsen as your child grows up they can cause vision to deteriorate further although treatment may be available. There aren’t any treatments for macular hypoplasia, optic nerve hypoplasia or nystagmus. If your child has any of these associated conditions their ophthalmologist will discuss the possibility of treatment with you.

Can aniridia be linked with other general health conditions?

Children with aniridia can also have conditions which affect other parts of the body as well as the eyes. This is because the PAX6 gene is also responsible for the development of other parts of the body as well as the eye. Therefore if the PAX6 gene does not function properly, other parts of the body can be affected as well as the eye.

What are the different types of aniridia?

There are three different types of congenital aniridia. The hospital will arrange an appointment with the appropriate specialists depending on the type of aniridia your child has.

67% of cases of congenital aniridia are familial. This means that it is caused by a ‘faulty’ gene inherited from a parent. It is usually inherited as an autosomal dominant trait. 

33% of congenital aniridia cases can occur sporadically meaning that it has not been inherited directly from either parent but that a new ‘faulty’ gene has started for the first time in that individual. This might only affect the PAX6 gene and cause simple aniridia but if several genes in a row are affected then it can cause syndromic aniridia and affect other parts of the body as well.

Aniridia (AN)-1 is inherited through the autosomal dominant inheritance (AD) pattern. (AN)-1 accounts for 66% of cases and only affects the eye not the rest of the body.

Aniridia (AN)-2 is sporadic, that means it is not inherited from either parent and this type accounts for 30% of aniridia cases. Children who have sporadic congenital aniridia may only have aniridia or they may also have a chance of having problems with other parts of their bodies. Children with (AN)-2 are at risk of developing one of two associated conditions, Miller Syndrome or WAGR Syndrome. There is more information on these conditions later in this information.

Aniridia (AN)-3: Can be associated with Gillespie Syndrome and accounts for 4% of aniridia cases. (AN)-3 follows the autosomal recessive (AR) inheritance pattern. If two carriers who show no obvious symptoms have a child, there is a 25% chance that he or she will have aniridia. There is more information on Gillespie syndrome later in this information.

Miller Syndrome

A child with (AN)-2 may have Miller Syndrome. Miller Syndrome is a very rare genetic condition thought to follow the autosomal recessive (AR) inheritance pattern. Miller Syndrome causes problems with the development of the face and the arms and legs such as cleft palate and small jaw.

WAGR Syndrome

Some children with aniridia (AN)-2 can also develop a tumour of the kidney called a Wilms’ tumour. When a child has a Wilms’ tumour and aniridia they will have a condition called WAGR Syndrome. The problems one child has because of WAGR may be different from another child with the same syndrome. Not all children with WAGR syndrome will have the same problems. Both boys and girls can have WAGR Syndrome. The word WAGR is made up of the initials of the problems that sometimes occur with the syndrome:

W: Wilms’ Tumour. A childhood tumour of the kidney. Children with AN-2 have a 30% risk of developing Wilms’ tumour before the age of 5 years old. If detected early Wilms’ tumour can be treated successfully.

A: Aniridia

G: Genitourinary problems. In boys this can cause undescended testicles. It can also cause the opening for urination to be in a different place than usual. In girls it can cause urinary problems and can affect the genitals.

R: (Mental) Retardation. This term is no longer used. "Learning disabilities" is now the preferred term.

Children with sporadic aniridia where a simple PAX6 gene fault cannot be found, or those who may be at risk of developing a Wilms’ tumour, usually have an abdominal ultrasonography on a regular basis. This is an examination with an ultrasound machine to show if there is a tumour developing on the child’s kidney.  If your child has sporadic aniridia they should have an abdominal ultrasound test every 3 months until they are 5 years old, then every 6 months until they are 10 years old and then every year until they are 16 years old or until your specialist thinks that further scans are no longer needed. These time frames may vary depending on what the specialists think is needed in each child's case.  If detected early Wilms’ tumour can be treated successfully.

Gillespie Syndrome

Children with Aniridia type 3 or (AN)-3 are at risk of Gillespie Syndrome. This is a rare, genetic condition which can cause aniridia and cerebella ataxia. Cerebella ataxia affects the parts of the brain responsible for co-ordination, balance and muscle tone. Cerebella ataxia can cause problems with walking unaided, writing and clear speech.

Your ophthalmologist will discuss with you what type of aniridia your child has and whether your child will need further testing or referral to a different specialist.

It is important to remember that for most children with aniridia, the eyes are the only part of the body which is affected.

Genetic counselling

All those with aniridia, whether sporadic or inherited from your parents, might pass the condition on to their children. As aniridia can be passed on as an inherited condition you may find it helpful to speak with a genetic counsellor. A genetic counsellor can explore things in more depth with you and your family. Genetic counselling is a free NHS service and you can ask your GP or your baby's ophthalmologist to refer you to your local genetic counselling service.

Genetic counselling aims to help you understand the type of aniridia your baby has, how it is likely to affect them in the long term and the risks of your baby passing on the condition to any children they may have. A genetic counsellor will ask about your family tree in detail to try and understand how your baby might have inherited aniridia.

Genetic testing

A genetic counsellor can also organise genetic testing if required. The results from genetic testing could provide useful information regarding the possibility of developing a related condition such as Wilms’ tumour or could help to rule this out. Testing is carried out in regional genetics centres and your baby's eye specialist (ophthalmologist) could refer you to one.

For more information on genetic conditions talk to your GP about the genetic services in your area or contact the Genetic Alliance UK.

Coping

Your child being diagnosed with an eye condition can be very upsetting. You may find that you are worried about their future and how they will manage. All these feelings are natural.

Some people may want to talk over some of these feelings with someone outside their circle of friends or family. RNIB can help, with our telephone Helpline and our emotional support service. Your GP or social worker may also be able to help you find a counsellor if you think this would help you.

Help to see things better

Aniridia can cause problems with your central vision. However, most children with aniridia have some vision that they can use every day and using their vision will not make their aniridia worse.

There are lots of things that your child can do to make the most of their vision. This may mean making things bigger, using brighter lighting or using colour to make things easier to see. Ask your ophthalmologist, optician or GP to refer your child to your local low vision service, which can provide you with equipment and tips on how your child can make the most of their vision.

Local social services should also be able to offer you information on play and development. They should also be able to offer you some practical support and help to signpost you.  

Our Helpline can also give you information about the low vision services available, education and employment advice, and the services available through the RNIB Children, Young People and Families team. Our website offers lots of practical information, support and signposting for parents who have a child with an eye condition.

How can light sensitivity be helped?

Aniridia usually causes light sensitivity, medically known as photophobia. Although there is no treatment for light sensitivity many children with aniridia can benefit from sun hats and sunglasses to protect their eyes from bright light or the sun.

  • Children who are light sensitive find that bright light causes discomfort. The level of discomfort can vary from child to child. You may wish to consider how to protect your child from bright light in different circumstances, for example:
  • Use sunlight diffusers on the back windows in a car
  • Do not suddenly put on bright overhead light in a dark room, especially when a baby is small and sleeps on their back.
  • You may notice your child turning away from certain light sources if it is making them uncomfortable which can help you know how to adjust things.
  • You may notice your child positioning their head at a certain angle to maximise their vision, or minimise light sensitivity. This can help you to know where to hold toys or place yourself when you are playing with your child.

What next?

Royal National Institute of Blind People
105 Judd Street
London
WC1H 9NE

Tel: 0303 123 9999
Web: rnib.org.uk

The RNIB Helpline can:

  • Put you in touch with an RNIB specialist advice service such as welfare benefits and rights, education, employment, legal rights, emotional support, daily living help and residential care
  • Send you free information and leaflets
  • Give you details of support groups and services in your area

Call us Monday to Friday 8:45 am – 5:30pm.

Low Vision Services can help people make the most of their sight. They:

  • are normally located within the hospital eye departments
  • are usually accessed through a referral from the hospital eye consultant or your GP.
  • offer a thorough assessment of vision and prescribe the appropriate magnifier for the individual.
  • provide training on how to best use the magnifier.
  • give advice on lighting which can be important in getting the most benefit out of the magnifiers.
  • give advice on maximising the use of peripheral vision.

Other sources of help

1. The Aniridia Network UK is a support group for people with Aniridia and their families.

Aniridia Network UK
22 Cornish House
Adelaide Lane
Sheffield
S3 8BJ

Web: http://aniridia.org.uk/
Email: info@aniridia.org.uk
Phone: 07792 867 949

2. Genetic Alliance UK is the national charity working to improve the lives of patients and families affected by all types of genetic conditions

Unit 4D, Leroy House
436 Essex Road
London
N1 3QP

Web: http://www.geneticalliance.org.uk/
Email: contactus@geneticalliance.org.uk
Phone: +44 (0)20 7704 3141
Fax: +44 (0)20 7359 1447

3. LOOK UK provides help, support and services for visually impaired children and their parents or carers. The LOOK helpline provides practical advice and emotional support, information about your child’s condition and contacting other families with similar problems by getting in contact with us through our enquiry service.

Tel: 0121 428 5038
Web: http://www.look-uk.org/ 
Email: information@look-uk.org

4. National Blind Children’s Society (NBCS) can offer information, support and advice to parents and carers of children with sight loss or an eye condition.

Tel: 01278 764 770
Web: www.nbcs.org.uk
Email: enquiries@nbcs.org.uk

5. Information on Miller Syndrome can be found at

http://www.faces-cranio.org/Disord/Miller.htm

6. International WAGR Syndrome Association

http://www.wagr.org/contactus.html

7. Information on Gillespie Syndrome can be found at

http://aniridia.org/conditions/gillespie.html

This information was last updated April 2014

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