A cornea transplant is an operation to remove all or part of a damaged cornea and replace it with healthy donor tissue.
A cornea transplant is often referred to as keratoplasty or a 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.
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.
The cornea helps to focus light rays on to 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 reaching the retina and causes the picture transmitted to the brain to be distorted or unclear.
The type of cornea transplant you have will depend on which part of the cornea is damaged or how much of the cornea needs replacing.
The options include:
The procedure usually takes less than an hour and, depending on your circumstances, you either leave hospital the same day or stay overnight.
If the procedure involves the transplantation of the outer cornea, the new outer cornea is held in place with stitches, which usually stay in for more than 12 months.
An endothelial transplant (EK) doesn't require stitches. It's held in place by an air bubble until a few days later, when it naturally sticks to the deep layer of the cornea.
In most cases, a cornea transplant procedure lasts less than an hour.
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.
Around 95% of full-thickness (penetrating) cornea transplants in low-risk conditions, such as keratoconus, last at least 10 years.
The recovery time for a cornea transplant depends on the type of transplant you have.
It takes about 18 months to enjoy the final results of a full-thickness transplant, although it's usually possible to provide glasses or a contact lens much earlier.
Recovery is usually faster after replacing just the outer and middle layers (DALK).
Endothelial transplants (EK) tend to have a faster recovery time of months or even weeks.
It's important to take good care of your eye to improve your chances of a good recovery.
This means not rubbing your eye and avoiding activities such as contact sports and swimming until you're told it's safe.
There is a shortage of donated corneas in the UK. Many more people would benefit from sight-saving surgery if more corneas were donated.
You can also call 0300 123 2323 if you wish to join the Organ Donor Register.