What is a cornea transplant?
A cornea transplant is an operation used to remove all or part of a damaged cornea and replace it with healthy cornea tissue from the eye of a suitable donor.
A cornea transplant is often referred to as a keratoplasty or corneal graft. It can be used to improve sight, relieve pain, and treat severe infection or damage.
One of the most common reasons for a cornea transplant is a condition called keratoconus, which causes the cornea to change shape.
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What is the cornea and what does it do?
The cornea is the clear outer layer at the front of the eyeball. It acts as a window to the eye. The coloured iris and the pupil (the black dot in the centre of the iris) can be seen through the cornea. It's made up of six delicate layers:
- the outer layer (the epithelium)
- the basement membrane
- Bowman’s layer
- the thick middle layer (the stroma)
- Descemet’s membrane
- the inner lining, which removes fluid from the cornea to keep vision clear (the endothelium)
The cornea acts like the lens on the front of a camera. Light rays are bent into the eye at an angle, enabling a picture to be projected onto the retina (the light sensitive film at the back of the eye). This ‘picture’ is then transmitted to the brain.
When the cornea is damaged, it can become less transparent or its shape can change. This can prevent light from reaching the retina and causes the picture transmitted to the brain to be distorted or unclear.
How is a transplant carried out?
There are several different ways to perform a cornea transplant, depending on which part of the cornea is damaged or how much of the cornea needs replacing: These include:
- a full thickness transplant - called a penetrating keratoplasty (PK)
- replacing or reshaping the outer and middle cornea - called a deep anterior lamellar keratoplasty (DALK)
- replacing deeper parts of the cornea - called an endothelial keratoplasty (EK)
A cornea transplant can be carried out under(where you are unconscious) or (where the area is numbed).
Around half of transplants are performed as day surgery. The other half require an overnight stay in hospital.
If the procedure involves the transplantation of the outer cornea, the new cornea is held in place with stitches, which usually stay in for at least 12 months. A transplant of the deeper layers of the cornea uses an air bubble instead of stitches to hold the transplant in place.
In most cases, a cornea transplant procedure lasts one to two hours.
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Are there any risks?
As with all types of surgery, there is a risk of complications resulting from a cornea transplant. These can include the new cornea being rejected by the body, infection, and further vision problems.
However, around 75% of cornea transplants last at least five years and around 65% may last up to 10 years.
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After a cornea transplant
The recovery time for a cornea transplant depends on the type of transplant you have. It can take up to two years for your normal vision to return after a full thickness corneal transplant or transplant of the front portion of the cornea (DALK). Partial transplants of the inner part of the cornea (EK) tend to have a faster recovery time of months or even days with the latest type of transplants.
It's important to take good care of your eye to improve your chances of a good recovery. This includes things such as not rubbing your eye and avoiding activities like contact sports and swimming until you're told it's safe.
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Cornea transplant risks
As with all types of surgery, there are several risks and possible complications involved with having a cornea transplant.
Some problems are obvious soon after surgery and need emergency treatment. Others may be spotted during follow-up appointments.
Rejection happens when your immune system recognises the donated cornea as a foreign body and attacks it. It is quite a common problem, occurring in about 1 in 5 corneal transplants.
Rejection can occur a few weeks after a cornea transplant, but it's more common after several months.
The problems can often be treated effectively with steroid eye drops if treatment begins as soon as you notice symptoms. Therefore, you should seek emergency specialist advice if you notice the symptoms below after a cornea transplant:
- red eye
- sensitivity to light (photophobia)
- vision problems, particularly foggy or clouded vision
- eye pain
As well as rejection, there is a risk of further problems after cornea transplant surgery. These can include:
- - where the cornea is not a perfectly curved shape
- - where pressure builds up in the eye due to trapped fluid
- - inflammation of the middle layer of the eye
- – where the thin lining at the back of your eye called the retina begins to pull away from the blood vessels that supply it with oxygen and nutrients
- the original eye disease (such as keratoconus) returning
- wounds from surgery reopening
- internal infection due to surgery wounds
After cornea transplant surgery
It's important to take good care of your eye after a cornea transplant to help ensure a good recovery and reduce the risk of complications.
After the procedure
Most people have to stay in hospital for one to two days after a full-thickness cornea transplant (penetrating keratoplasty). You may be able to go home on the same days of the procedure if you have a partial-thickness transplant.
Your eye may be covered with an eye pad or plastic shield, which is removed the day after the procedure. When it is taken away, you may find that your sight is blurred. This is normal.
There should not be serious pain after the operation, but there might be some swelling and discomfort.
If you have had a type of partial-thickness transplant that uses an air bubble instead of stitches to hold the transplant in place (an endothelial keratoplasty), you may be asked to lie on your back as much as possible in the first day or two after surgery. This can help the bubble hold the transplant in the correct place. The bubble will be absorbed after a few days.
Looking after your eye
Once you return home after the procedure, you will need to take good care of your eye. Some important points to remember include:
- don’t rub your eyes
- during the first weeks after surgery, avoid strenuous exercise and heavy lifting
- if you have a job not involving physical strain, you can return to work two to three weeks after surgery
- if your job involves manual labour, you should wait for three to four months
- avoid smoky or dusty places as they could irritate your eyes
- if your eye is sensitive to light, wearing sunglasses can help
- avoid contact sports and swimming until given clear advice that it's safe, and wear protective goggles when resuming contact sports
- bath and shower as normal, but be careful not to get water in your eye for at least a month
- don’t drive until your specialist tells you it's possible
You will usually be given a patch to wear at night for the first few weeks after surgery to help protect your eye.
For all types of cornea transplant, you have to use steroid or antibiotic eye drops daily. These are normally required for several months, although some people may need to use them for more than a year. The drops reduce swelling and inflammation and help to prevent infection and rejection.
At first, you will need to attend regular follow-up appointments. These should gradually become less frequent over time.
If stitches were used to hold transplant in place, these are left in place initially to allow the cornea to heal. They are usually removed over the course of a year.
The time it takes for your vision to return after a cornea transplant largely depends on the specific procedure used. In some cases, your vision may fluctuate between being better or worse before it settles down.
Typical recovery times for the most common types of cornea transplant are:
- penetrating keratoplasty (PK) - up to two years
- anterior lamellar keratoplasty (ALK) - a few weeks
- deep anterior lamellar keratoplasty (DALK) - up to 12 months
- Descemet's stripping endothelial keratoplasty (DSEK) - around four to eight weeks
- Descemet’s membrane endothelial keratoplasty (DMEK) - around two weeks
Even after your vision returns, it's likely you will need corrective lenses. In some cases, laser treatment is used after your eyes have healed to correct vision problems.
There are a number of different types of cornea transplant procedure, depending on the parts of the cornea that need to be replaced.
Most cornea transplant operations involve transplanting the full thickness of the cornea. However, recent advances in technology mean it is sometimes possible to only transplant a part of the cornea.
Full thickness transplants
A 'full thickness' transplant is called a penetrating keratoplasty (PK).
During this procedure, a circular piece of damaged cornea from the centre of your eye is removed and replaced with the donated cornea. In most cases, a circular cutting instrument (similar to a cookie-cutter), called a trephine, is used to remove the damaged cornea.
The new cornea is held in place by tiny stitches, which sometimes form a star-like pattern around the edges. You may be able to see the stitches faintly after the operation.
The operation may be done underor and usually takes one to two hours. If local anaesthetic is used, you won't be able to see through the eye during the operation as the anaesthetic temporarily stops the eye from working.
Most people have to stay in hospital for one to two days after a full-thickness cornea transplant.
Partial thickness transplants
Recently, techniques have been developed that allow only parts of the cornea to be transplanted. These techniques aren't suitable for everyone in need of a cornea transplant and they can take longer to perform, but they often have a faster recovery time and a lower risk of complications.
There are several different techniques your surgeon may use, depending on which layers of the cornea are transplanted. Generally, these techniques can be broken down into transplants involving the front portion of the cornea and those involving the back portion.
Most of these procedures are carried out using cutting instruments (such as a trephine), although lasers are sometimes used. These procedures can be carried out using either local or general anaesthetic and you may be able to go home on the same day of the procedure.
Transplanting the front portion of the cornea
The main techniques for transplanting the front parts of the cornea include:
- removing and replacing only the outer layers of the cornea - anterior lamellar keratoplasty (ALK)
- removing and replacing the outer and middle layers of the cornea, but the inner layers are left intact - deep anterior lamellar keratoplasty (DALK)
Like a penetrating keratoplasty, stitches are used to fix the donated cornea in place during both of these procedures.
Transplanting the back portion of the cornea
The main techniques for transplanting the back parts of the cornea include:
- replacing the inner lining of the cornea together with about 20% of the corneal supporting tissue (corneal stroma) - Descemet's stripping endothelial keratoplasty (DSEK)
- replacing only the inner layer of cells of the cornea - Descemet’s membrane endothelial keratoplasty (DMEK)
DMEK is a new technique that allows faster and near complete visual recovery with low long term risks such as rejection (less than 1%).
Stitches aren't used during either of these procedures, instead the donated tissue is held in place using a temporary air bubble.
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Why are cornea transplants performed?
Cornea transplants are usually performed to correct problems with your eyesight caused by certain medical conditions.
They are also sometimes used to relieve pain in a damaged or diseased eye, or treat emergencies such as severe infection or damage.
Some of the most common reasons for requiring a cornea transplant are described below.
Keratoconus is a condition that causes the cornea to weaken, get thinner and change shape. It affects about 1 in 2,000 people. The exact cause of the condition is unknown. It's possibly passed down through the family, or due to an allergy.
Keratoconus is one of the most common reasons for corneal transplantation in younger patients. It doesn’t usually appear until the early teens, but can occur earlier in a few patients.
Many cases of keratoconus are mild and can be managed by using contact lenses or glasses. But in some patients it can progress to the point where a corneal transplant is necessary.
Certain conditions may affect the eyes and cause them to slowly develop problems over time.
One example of this is Fuch’s endothelial dystrophy, where functioning of the cells lining the inner cornea (the endothelium) begins to deteriorate. This happens faster as you get older. As the cells weaken, instead of clearing excess fluid it allows it to build up, leading to cloudy vision.
A cornea transplant may also be performed if:
- a small hole develops in the cornea due to damage (known as corneal perforation)
- an infection in the cornea doesn't respond to antibiotics and keeps returning
- the cornea is scarred due to an infection or injury
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