Medical Information on Corneal 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 to 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.
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.
A Corneal Dystrophy is a very rare condition of the window at the front of the eye (cornea). A Dystrophy is a condition that a child is born with. Children are usually at first not affected by a dystrophy. Normally the cornea is clear, smooth and comfortable. A child with a corneal dystrophy at first may also have a clear, smooth and comfortable cornea. With time however they may develop a hazy cornea that becomes bumpy and feels gritty. They often also complain of blurred vision.
There are many different kinds of Corneal Dystrophy conditions
There are many different kinds of Corneal Dystrophies. Their names often describe how they look (Granular Dystrophy) or who first described the condition (Fuch's Dystrophy). The different dystrophies affect different layers of the cornea. The cornea has three layers:
- The top or outside layer is called the 'epithelium'
- The middle layer is called the 'stroma'
- The bottom or inside layer is called the 'endothelium'
The top or outside layer is called the epithelium
The epithelium is the thin outside layer, like skin. If it is damaged it can quickly grow back, just like skin. The names of the Corneal Dystrophies that affect the surface of the cornea include:
These kinds of dystrophies tend to cause gritty, uncomfortable eyes as their main symptom. This may be worse in bright light. If bright light makes eye pain worse children will try to avoid daylight and well-lit rooms. This is called photophobia.
The middle layer is called the stroma
The stroma is the thickest layer. It is strong and made of the same stuff as the 'white' of the eye, except it is clear. If this layer is damaged it can often heal leaving a hazy scar. The names of the corneal dystrophies that affect the middle layer of the cornea are all named by how the look:
These dystrophies tend to cause glare and blurred vision as their main symptoms. Less frequently they may also cause gritty, uncomfortable eyes.
The bottom or inside layer is called the endothelium
The endothelium is very thin and fragile. This layer helps keep the cornea clear. It 'pumps' water out of the stroma, keeping it 'dry' and clear. If this layer becomes damaged the stroma can become hazy. If the endothelium is damaged it cannot grow back and fix itself. The Corneal Dystrophies of this layer include:
- Congenital Hereditary Endothelial Dystrophy
- Posterior Polymorphous Dystrophy
These dystrophies tend to cause blurred vision as their main symptom.
All the different dystrophies can affect children at different ages and in different ways
All the different dystrophies can affect children at different ages and in different ways. Sometimes the child develops problems soon after birth. Often the Dystrophy is not a problem until the child is in their teens. The child may complain of a gritty eye, other times blurred vision and often both together.
Most Corneal Dystrophies are caused by a mistake 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 mistake in the chemical alphabet then a part of the body may not work correctly. A child with a Corneal Dystrophy has often been passed (inherited) a gene with a mistake 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. The mistake in the gene normally only affects one layer of the cornea. There are many different ways a child can 'inherit' a condition.
Corneal Dystrophies often cause the cornea to become hazy. This usually causes blurring of vision. 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 can often be the main symptom.
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. Most children however with a corneal dystrophy slowly develop a hazier cornea as time passes. As the cornea becomes hazier the children are more likely to complain of blurred vision.
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 can be worse in bright light because of glare.
If the cornea has been hazy from an early age then the child may develop a 'lazy' eye. 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 the 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.
Some children with Corneal Dystrophy also sometimes have other problems with their eyes
Some children with Corneal Dystrophy also sometimes have other problems with their eyes. Myopia and Nystagmus may also be seen along with hazy corneas in children. These other eye conditions may cause reduced vision even though the corneas have been replaced with clear ones. See the VI Scotland Documents on these conditions.
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.
Young children with Corneal Dystrophy may complain of sore eyes or blurred vision. They may say the eyes are gritty and that bright light hurts them (photophobia). 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.
Many things can be done to help. If the eyes are gritty, eye drops can help smooth the surface of the eye. A contact lens can also be worn which often makes the eye more comfortable. If bright light makes the pain worse (photophobia) then sunglasses and a sunhat can help.
Blurred vision can be improved by wearing spectacles or contact lenses. If this does not help then sometimes laser surgery can reduce the haziness of the cornea. If the cornea is still very hazy and the vision very blurred an operation may be the only way to improve vision. 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. 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).
If 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.
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). Patching of the good eye may need to be done to encourage the poorer eye to see. The child will have to attend the hospital quite often for checks.
What are the possible complications of a corneal graft operation?
There are many possible problems that can develop after a corneal graft operation. These include:
- Graft Rejection
Because the new cornea is not the child's own their immune system may try to reject it. If the eye becomes very sore and red after the operation and the vision becomes worse rejection may be starting. If this happens the child needs to see an eye doctor urgently. By taking lots of eye drops regularly and sometimes tablets the rejection can often be treated.
Sometimes the pressure in the eye can become high after an operation. The pressure can cause damage to the optic nerve. Drops can often help to reduce the pressure.
Infection is very rare but can cause severe loss of vision
Luckily infection within the eye is very rare after a corneal graft operation. If a child's eye becomes red and sore after a cataract operation then they need to tell their eye doctor quickly. Usually infections can be treated with antibiotics.
Even if no complications occur a corneal graft operation may not always mean a child will see perfectly well.
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 photophobia. 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 corneal dystrophy 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.
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.