Visually Impairing Conditionsby Dr Andrew Blaikie for VI Scotland
Medical Information on Peter's Anomaly
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
- The effects of the condition on the child's vision
- How the condition is diagnosed
- 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.
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
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. If you have any questions or comments regarding the information please contact:
Visual Impairment Scotland
Scottish Sensory Centre
The University of Edinburgh
Edinburgh EH8 8AQ
Telephone Number : 0131 651 6078
Fax Number : 0131 651 6502
Textphone : 0131 651 6067
Medical Information on Peter's Anomaly
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 Peter's Anomaly?
The sclera is the tough 'white' of the eye. The sclera gives the eye its overall shape and strength. A child can be born with most of the normally clear cornea hazy and white, like the sclera. This is called Sclerocornea. If only the central part of the cornea is hazy then this is often called Peter's Anomaly.
What is the cause of Peter's Anomaly?
Most cases of Peter's Anomaly occur by chance. Sometimes the condition runs in families. A child may then 'inherit' the condition from one parent. This is called autosomal dominant inheritance. Occasionally the condition can occur for the first time in a family as a result of marrying a cousin or a more distant relative. This is called recessive inheritance.
How does Peter's Anomaly affect the way a child sees?
If the normally clear cornea is hazy and white, vision will be blurred. The more hazy the cornea becomes the more blurred the vision will be. Vision can be worse in bright light because of glare. Glare occurs when light is scattered by the hazy cornea. This is like trying to look through a dirty car windscreen into low bright sunlight or approaching car headlights. The condition usually affects both eyes. One eye is may be less affected than the other.
Most young children who are born with hazy corneas in both eyes will 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.
How blurred the vision might become depends on:
- How hazy the cornea is.
- What part of the cornea is hazy.
- Whether the child has developed a 'lazy' eye.
- Whether the eye has other conditions that might reduce vision.
If only a small area of the cornea is hazy, away from the centre, then the child is likely to have good vision. If the centre of the cornea is very hazy, not letting much light in, then the child is more likely to have poor vision. This is usually the case in Peter's Anomaly.
Because the cornea is hazy from the time of birth the eye may become 'lazy'. This is also known as Amblyopia. It is not actually the eye that has become lazy; it is the special vision parts of the brain. The brain can only learn to see as clearly as the picture given to it by the eyes. If the brain has not been given a sharp, clear picture by the eye because of the hazy cornea then it cannot learn to see clearly. If a hazy cornea is replaced by a new, clear cornea (corneal graft operation) the vision may still be blurred. This is because the brain has not developed the power to see clearly. This is called Amblyopia. See the VI Scotland Document on Amblyopia. Because of other complications and difficulties with corneal grafting this operation is rarely recommended to treat Peter's Anomaly in the United Kingdom.
Some children with Peter's Anomaly also sometimes have other problems with their eyes
Some children with Peter's Anomaly also sometimes have other conditions of the eyes. These might include:
- Glaucoma, damage to the nerve of sight from raised pressure in the eye.
- Nystagmus, constant to and fro movements of the eyes.
- Microphthalmia, a small eye.
- Cataract, a hazy lens
- Retinal Detachment
These conditions may also cause visual impairment. See the VI Scotland Documents on these conditions for a more detailed discussion.
How is Peter's Anomaly diagnosed?
When a baby is born doctors examine the eyes to see if they are normal. If any problems are noticed they can then ask an eye doctor to perform further tests. 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.
It is usually difficult to examine a newborn's eyes closely. It is a lot easier if the child is asleep. With the help of an anaesthetist a young baby can be briefly anesthetised. While the baby is asleep an eye doctor can examine the eyes more closely. This can help confirm that the cornea is hazy. It can also make sure there are no other problems with the eyes. The eyes can also be checked to see if the child might benefit from spectacles.
What can be done to help?
Many things can be done to help. Blurred vision can sometimes be improved by wearing spectacles or contact lenses. Wearing dark glasses or a sun hat may help problems with glare.
It is important that families with a child affected by Peter's Anomaly receive counselling from a specialist in genetics. Sometimes the condition runs in families. A future child or grandchild may also be affected.
If both corneas are very hazy and the vision very blurred an operation may be the only way to help. A corneal graft operation is then needed. With the child asleep (under a general anaesthetic) the hazy cornea is cut away and replaced with a clear one. If other eye conditions are present, such as cataract this is also treated at the same time. The new clear cornea is donated from a person who has died. This prevents the child growing up with blurred vision and developing lazy eyes (amblyopia).
The operation is very difficult to do. Complications may develop such as inflammation, infection or high pressure in the eye. Even after an operation many things still need to be done to make sure the operation is a success. The child will need lots of drops in their eyes every day for many months. The child may also have to wear spectacles or a contact lens. One eye may not see so well as the other. This may be because it is lazy (amblyopic). The child will have to attend the hospital quite often for checks. Sometimes an operation improves vision a lot. More often it only makes a small improvement. Sometimes it does not help at all.
If only one eye is affected an operation is rarely recommended. If both eyes are affected but the corneas are not too hazy it can be more difficult to decide if an operation is needed or not. It is sometimes difficult in younger children to tell how well they are seeing. Often it can be better to wait until the child is a little older before making the decision to do a corneal graft operation. When a child is older the eye doctor can be surer what the child's level of vision really is.
Children with Peter's Anomaly often also have glaucoma
Glaucoma is when the optic nerve is damaged by high pressure in the eye. Drops can sometimes lower the pressure in the eye. More often an operation is needed to help reduce the pressure.
Are there any other conditions associated with Peter's Anomaly?
Children with Peter's Anomaly usually only have problems with their eyes. Sometimes however especially if both eyes are affected they may also other conditions as well. These may include:
- Learning difficulties
- Problems with the heart
- Problems with some parts of the brain
- Typical appearance to the face
- Short height
- Difficulty with toilet training
When some of these other problems also occur the condition is often called Peter's Plus Syndrome.
How can parents, family, friends and teachers make a difference?
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 and tinted glasses can also help reduce symptoms of glare. If your child has also been prescribed drops they should be used regularly as advised by the nurses and doctors at the eye clinic.
We use our vision to get around, learn new things and to meet other people and make friends.
Most children with cataracts and who have been treated 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 their own 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 an (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.