– What causes corneal dystrophies?
– What types of corneal dystrophies are there?
– Epithelial dystrophies
– Stromal dystrophies
– Endothelial dystrophies
What causes corneal dystrophies?
Corneal dystrophies can often run in families, but may not always do so. In some cases it may not be possible to say why someone has developed their corneal dystrophy.
There are two ways that corneal dystrophies can be inherited (passed on in families):
- Dominant inheritance. This means that one parent actually has the condition. Each time that parent has a child there is a 50 per cent (one in two) chance of the child having the condition as well.
- Recessive inheritance. This means that neither of the parents has the condition themselves, but both are “carriers”. If two carriers have children, there is a 25 per cent (one in four) chance that each child will have the condition. Both parents need to be carriers of the condition for their child to be affected.
What types of corneal dystrophies are there?
The cornea is made up of layers. Each layer has a different role in keeping the cornea healthy and clear. Corneal dystrophies can be described in many different ways, but because each dystrophy will start by affecting a particular layer of the cornea, they are often classified by layers of the cornea they affect.
The layers of the cornea are the epithelium, Bowman’s layer, the stroma, Descemet’s membrane and the endothelium.
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The epithelium is the thin outermost layer of the cornea. It is a barrier protecting the rest of the cornea and the inside of the eye from foreign bodies, such as grit, and from infections. The epithelium is filled with tiny nerve endings that make the cornea very sensitive to touch. The epithelium also provides an extremely smooth surface, which is essential for good vision.
A common symptom of corneal dystrophies that affect the epithelium is a painful “foreign body” sensation, which can feel like there is something in your eye. This can occur if there is a change in the cornea which disturbs the epithelium.
One cause of foreign body sensation can occur when the surface epithelial layer breaks down exposing the sensitive nerve endings. This breakdown of the corneal surface is known as an “erosion” and causes a similar feeling to when an eyelash or a piece of grit gets into the eye, but in some cases can be a lot more painful.
The epithelium can heal quickly so you may not experience these symptoms for very long. Treatment can also be given to relieve your symptoms and aid healing.
Epithelial basement membrane dystrophy (also known as map dot fingerprint dystrophy or Cogan’s dystrophy)
This is the most common epithelial dystrophy. Most people have no symptoms. About 10 per cent of people who have this dystrophy develop recurrent corneal erosions. These can cause pain, light sensitivity, blurred vision, redness and watering and you may not be able to open the affected eye. Most people that have these symptoms are over 30 years of age.
Erosions occur because this dystrophy changes the “basement” or anchoring layer of the epithelium, which can cause small areas of the top layer of the cornea to become detached. When an optometrist (optician) or ophthalmologist (hospital eye doctor) examines your cornea these changes can look like the shapes of land on a map, dots or fingerprints.
Although corneal erosions can be painful, they normally heal very quickly, sometimes within hours of the erosion happening. If you have corneal erosion then you will usually have treatment to relieve pain and allow the cornea to heal.
The treatment you will be given will depend on how bad the erosion is and whether or not you have had many erosions before. If you need treatment this will usually be eye drops to dilate (enlarge) your pupil. These drops will blur your vision, but help to reduce pain by keeping the movement of the inside of the eye to a minimum while your cornea heals.
You will also be given antibiotic eye drops to help prevent infection as well as lubricating drops, gels or ointments to make your eyes feel more comfortable and prevent the inside of your eyelids sticking to or damaging the epithelium.
If you have very frequent severe erosions, other treatments such as “bandage” contact lenses (worn long-term to keep the eye comfortable), or ‘debridement’ (where scar tissue is removed from the surface of your cornea) may be needed to allow your cornea to heal.
Typically, erosions can flare up from time-to-time and settle again without causing any long term problems with sight. Most people do not have sight problems and everyday activities such as driving or reading are not affected in the long term. It is very rare that someone with an epithelial basement membrane dystrophy will need a corneal transplant.
This is a very rare corneal dystrophy, which is inherited by the dominant method. This condition causes tiny round pockets of fluid, known as cysts to form in the epithelial layer of your cornea. These develop early in life, sometimes within the first year and can increase in number over time. Meesman’s dystrophy usually affects both eyes.
The cysts do not normally cause any symptoms until late adolescence or adulthood, when they can start to break open (rupture) on the surface of the cornea and cause discomfort. These changes may make you light sensitive, make your eyes water and you may have a ‘foreign body’ sensation. Some people may experience temporary episodes of blurred vision. This dystrophy may also make it difficult to wear contact lenses.
Meesman’s dystrophy is usually treated with eye drops to lubricate the front of the eye to help reduce symptoms and make your eyes more comfortable. Although people can have temporary flare-ups when cysts rupture, Meesman’s dystrophy does not worsen over time so other treatments are not normally required.
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The stroma is the middle layer of the cornea. It makes up around 90 per cent of your cornea’s thickness. The stroma is made up of water and a material called collagen, which is arranged in regular fibres. This regular arrangement of collagen fibres means that the stroma is clear and also very tough and elastic.
Stromal dystrophies cause deposits to build up in this layer. These deposits make your stroma less clear, affecting vision. Changes in your stroma can also affect other layers of your cornea causing symptoms such as corneal erosions to develop.
Reis-Bücklers dystrophy is a very rare condition that often starts in childhood around the age of four or five or in early adulthood.
Reis-Bücklers dystrophy affects a part of the cornea called the Bowman layer. The Bowman layer is the top layer of the stroma, separating it from the epithelium. In this dystrophy the tissue that makes up the Bowman layer and the basement layer of the epithelium changes, causing painful erosions to develop.
Over time, although the erosions may settle down the surface of the cornea can become hazier, affecting sight.
Reis Buckler dystrophy affects both eyes equally. The changes it causes tend to be in the middle of the cornea, so they are more likely to affect your vision. Reis-Bucklers corneal dystrophy can also cause a loss of sensation (feeling) to the surface of your cornea, which could mean you may not be aware if something goes in your eye, or if your cornea has been damaged. This could lead to further damage.
Treatments for Reis-Bucklers corneal dystrophy can include removing scar tissue from the surface of your cornea (epithelial debridement) or laser eye surgery to remove the cloudy area of the cornea.
If Reis-Bucklers dystrophy causes very poor vision, a corneal transplant may be needed.
Lattice dystrophy is the most common dystrophy affecting the stroma. It is inherited by the dominant method and usually begins before the age of 20 years. Early symptoms tend to be a “foreign body” sensation, which can feel like there is something in your eye and a slight change in vision. Some people may experience painful corneal erosions, but others have no symptoms.
When your eye is examined under a microscope, very fine glassy-looking overlapping lines and dots can be seen in your cornea. As the dystrophy progresses, these lines become thicker and may make the cornea hazy affecting sight.
If you have “foreign body” sensations and erosions then you will be given treatment for these, which might include antibiotic eye drops or artificial tears. If you experience serious sight loss, laser treatment or corneal transplant might be required.
This dystrophy affects both eyes and is inherited by the dominant method. Changes to your cornea usually begin before the age of 20. In early stages vision isn’t affected, but when your eyes are examined using a microscope, small white deposits, which look like crumbs, sugar granules, rings or snowflakes can been seen in your cornea.
Slowly, over time these deposits increase in number and join together becoming larger and noticeable without a microscope.
Vision is not usually severely affected under the age of 50, but as the dystrophy worsens you may experience frequent erosions and “foreign body” sensation, which can feel like there is something in your eye, may be a problem. You may also experience glare and light sensitivity because of the increase in deposits.
If you develop erosions and your eyes are painful or uncomfortable eye drops can be given to help soothe your eyes and allow the cornea to heal.
If the erosions are very frequent and not helped with drops, you may need laser treatment to remove some of the deposits and smooth the surface of the cornea to try to prevent or lessen these. Your cornea may also become less sensitive to touch and pain due to the dystrophy. This can mean that you may not be aware that you are developing erosions or that your cornea is damaged.
If you experience serious sight loss due to granular dystrophy, a corneal transplant may be required.
This dystrophy is inherited by the recessive method, which makes it less common, but more severe, than other stromal dystrophies.
Macular dystrophy causes dense greyish-white deposits to form in the stroma. With time more and more of these develop eventually causing the whole stroma to become cloudy.
These changes also cause the cornea to become thinner and irregular in shape. As well as reducing vision, macular dystrophy can also make someone sensitive to light and cause painful erosions to develop.
Often between the ages of 20 to 40 there will be serious sight loss due to this dystrophy. You may need a corneal transplant.
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The endothelium is an extremely thin single layer of cells, which makes up the innermost layer of your cornea. This layer is vital for keeping the cornea clear, as it acts as a pump controlling the movement of fluids and nutrients in and out of your cornea.
Without this pump, the cornea can swell with fluid and become hazy. This layer cannot repair itself, so conditions that affect the endothelium can cause swelling of the cornea that can lead to serious sight loss.
Fuchs endothelial dystrophy
Fuchs corneal endothelial dystrophy is inherited by the dominant method. As a normal part of getting older, a small number of endothelial cells are lost. This does not normally cause any changes in vision. In Fuchs dystrophy, this process speeds up and more cells than usual are lost.
Eventually, enough cells are lost that the endothelium doesn’t work well enough to prevent fluid soaking into the cornea or as a pump to remove it. This causes the cornea to swell due to the build-up of fluid, known medically as “oedema”. This oedema can affect vision.
Fortunately, Fuchs dystrophy develops slowly. It is normally detected when someone is in their fifties or sixties. Not everyone who is diagnosed with it experiences problems with their vision. As it develops it can cause sensitivity to light and can make vision cloudy.
If the changes to your sight are starting to cause you difficulties, your specialist may recommend that you have a corneal transplant.
Being diagnosed with an eye condition can be very upsetting. You may find that you are worried about the future and how you will manage with a change in your vision. We’re here to support you every step of the way, and to answer any questions you may have – just get in touch with our Sight Loss Advice Service.
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