Cornea Transplant Types, and Why a Surgeon May Replace Only Part of the Cornea

People often talk about a cornea transplant as if it were a single operation. It is not. Surgeons today have several ways of replacing a damaged cornea, and the choice depends on which layers of the cornea are diseased. Some operations replace the whole thickness of the cornea, and others replace only a thin layer. Knowing the main cornea transplant types helps families understand what the surgeon is proposing and why. This guide draws on the patient information from the American Academy of Ophthalmology, and it is general education, not advice about any one eye.

What the cornea does

The cornea is the clear front window of the eye. It helps to focus light into the eye so that you can see. It is made of layers of cells, and those layers work together to protect the eye and to give clear vision.

For good vision the cornea must be clear, smooth and healthy. If it is scarred, swollen or damaged, light is not focused properly. The result is blurred vision, or glare. A transplant is considered when the cornea cannot be healed or repaired.

What can damage a cornea

The Academy’s guide to corneal transplantation lists some common causes.

• Keratoconus. The cornea becomes cone-shaped instead of dome-shaped.
• Fuchs’ dystrophy. Cells in the inner layer of the cornea stop working effectively.
• Infections and injuries. Either one can leave scars on the cornea.
• Earlier surgery. Previous corneal surgery or other eye surgery can damage the cornea.

A wider look at why damaged corneas are such a common cause of sight loss is in a guide to corneal blindness and cornea transplant.

Where the new cornea comes from

In a corneal transplant, the diseased cornea, or part of it, is replaced with clear, healthy tissue from a human donor. A donor is someone who chooses to give their corneas after their death to people who need them. The Academy states that all donated corneas are carefully tested to make sure they are healthy and safe to use.

Two other guides on this site explain the donor side of the story. One covers who can donate their eyes. The other explains how cornea shortages and waiting lists affect patients.

Full thickness transplant

If both the front and the inner layers of the cornea are damaged, the entire cornea may need to be replaced. This is called penetrating keratoplasty, or PK, and it is also known as a full thickness corneal transplant. The surgeon removes the diseased cornea. Then the clear donor cornea is sewn into place.

Two things are worth knowing. First, recovery is longer than after other types. The Academy says that getting complete vision back after PK may take up to one year or longer. Second, there is a slightly higher chance that the body will reject the new cornea than with other types of transplant.

Partial thickness transplant

Sometimes only the front and middle layers of the cornea are damaged. In that case the surgeon removes only those layers and keeps the thin back layer, which is called the endothelium. The operation is called deep anterior lamellar keratoplasty, or DALK, and it is also described as a partial thickness transplant.

The Academy says DALK is commonly used to treat keratoconus, in which the cornea bulges. Healing is shorter than after a full transplant. There is also less risk of the new cornea being rejected.

Endothelial keratoplasty

In some eye conditions the innermost layer of the cornea, the endothelium, is the part that is damaged. This causes the cornea to swell, and it affects vision. Endothelial keratoplasty replaces only that inner layer with healthy donor tissue. It is counted as a partial transplant because the rest of the cornea is left alone.

There are a few kinds. The Academy names two.

• DSEK, or DSAEK. This stands for Descemet’s stripping endothelial keratoplasty. The donor tissue is thicker, so it may be easier to transplant and position.
• DMEK. This stands for Descemet’s membrane endothelial keratoplasty. The donor tissue is thin and can be harder to transplant. Because it is thinner, recovery is quicker.

Both remove damaged cells from an inner layer called Descemet’s membrane, through a small cut. Then the new tissue is put in place. Just a few stitches, if any, are needed to close the cut. Much of the cornea is left untouched, which lowers the risk of the new cells being rejected.

How the surgeon decides

The Academy is clear that the surgeon makes the choice, based on the condition of your cornea. The differences it describes can be summed up like this.

• Full thickness surgery has the longest recovery, and healing after DALK is shorter.
• Full thickness surgery carries a slightly higher chance of rejection than the partial types.
• Endothelial surgery leaves much of the cornea untouched, which lowers the chance of rejection.
• Not every condition suits every type. DALK is used for problems of the front layers, and endothelial surgery for problems of the inner layer.

If you are told that you need a transplant, ask which of these types is planned and why that one was chosen.

Before the operation

Your ophthalmologist will talk with you about why you need the surgery, how it can help you see, and what to expect during and after it. Once you decide to go ahead, a date is chosen. That date may change if a good donor cornea is not ready for you at that time.

Tell the surgeon about every medicine you take, because some may need to be stopped. The Academy says you may need to stop blood thinners and may need a physical examination or other tests to make sure you are healthy enough for surgery. You will not be able to drive after the operation, so arrange for someone to take you home.

On the day

A corneal transplant is done as an outpatient procedure. Eye drops go into your eyes, and you may be given a medicine to help you relax. The surgeon uses either local or general anaesthetic, so you do not feel pain. A device keeps the eye open. Even with the eye open, you will see very little or nothing.

The surgeon then transplants the donor tissue in the way that suits your eye. In some cases a circle of cornea is removed and replaced with a matching piece of donor tissue, which is stitched in. In others, only a very thin front layer is removed and replaced. In an endothelial transplant, only the damaged inner layer is removed and a thin disc of donor tissue is placed on the back of the cornea. An air bubble is then put in the eye to push the new layer into place.

Sometimes other problems are repaired in the same operation, such as a cataract. After surgery a shield is usually taped over the eye. You are watched until you have recovered from the anaesthetic, and you are told how to look after the eye at home.

Recovery at home

You go back to the surgeon the day after the operation to have the eyes checked. Whether the stitches are removed depends on how quickly you heal, the health of your eye and the type of stitches used. Depending on the type of transplant, some people must lie on their back for a while so that the donor tissue stays in place.

• Use the eye drops exactly as prescribed.
• Do not press on or rub the eye.
• Wear glasses or an eye shield to protect the eye.
• If you need pain relief, ask the doctor which medicines are safe to take.
• Ask when you can return to normal activities.

Be patient. Depending on the type of transplant and how the eye heals, it can take a year or more to recover fully.

Rejection and its warning signs

Rejection means that the immune system sees the new tissue as something that should not be there and tries to get rid of it. The Academy says rejection is a problem for up to 3 out of 10 people who have a full thickness transplant. The risk is lower with partial thickness operations. Prompt treatment with steroids can sometimes reverse rejection and save the transplant.

That is why the warning signs matter. They are eye pain, extra sensitivity to light, redness of the eye, and cloudy or hazy vision. Tell the ophthalmologist right away if any of them appears. Do not wait for the next appointment.

Other problems that can follow

Sometimes a transplant causes other eye problems, such as infection, bleeding, a detached retina or glaucoma. Even when the transplant does its job, other conditions may limit vision. The new cornea might not be curved evenly, which is astigmatism. Or the eye may have a separate disease, such as macular degeneration, glaucoma or diabetic retinopathy.

Some people need more than one transplant. The first graft may be rejected, or other problems may occur. The Academy says a repeat transplant has a higher rate of rejection than the first one.

Questions to ask the surgeon

• Which type of transplant is planned for my eye, and why?
• How long is the recovery likely to be for that type?
• Will stitches be used, and when will they come out?
• Which drops will I use, and for how long?
• What are the warning signs of rejection, and whom do I call?
• Can any other problem be repaired during the same operation?

Taking it further

If a transplant is being discussed for you or someone in your family, write down your questions before the next visit. For questions about cornea transplant options, ask PEBS about cornea transplants. People who would like to give can review the hospital’s donation methods.

A cornea is built in layers, and the operation is matched to the layer that has failed.

This article is general information and does not replace an examination by an eye doctor.