Can we know when a herpetic keratitis will reappear?
A cornea transplant is a surgical procedure whereby we replace the patient's diseased cornea with a healthy cornea from a donor.
The cornea is a fine transparent layer that covers the eyeball, in front of the iris and the pupil. It has multiple functions: as a transparent window into the eye it lets images pass through it and acts as a poweful lens to focus them on the retina.
The retina is a nerve tissue that sends the images to the brain and allows us to the objects that surround us.
The cornea may change due to opacities (acquired or congenital), primary or secondary oedema, or a deformation, most commonly keratoconus, which all cause a loss of vision.
The surgical procedure is performed when an opacity or deformation is detected, or there is any type of disease that affects the transparency of the cornea.
There may be multiple causes such as infections, trauma, dystrophy, degenerations or corneal disorders after cataract surgery, for example, which cause a secondary corneal opacity or a deformation thereof.
In these cases, what we perform is called a keratoplasty, which involves replaces the damaged cornea with a donor cornea.
Cornea transplant surgery involves replacing the pathological cornea with a healthy cornea from a donor. The tissue meets the legal requirements as well as the analytical tests necessary for donation according to current legislation. The donation is anonymous and altruistic.
There is a special situation around autotransplantation, where it is the cornea from the patient themselves that is rotated to avoid any opacity, or the cornea from the other eye is used.
It is an operation that usually lasts approximately 45-90 minutes, depending on the compexity of the cases. It is undertaken in the theatre under local or general anaesthesia, and a trepan and specific instruments are used to transplant the cornea. We remove the cornea, or the cornea layer that is affected, we suture it and put it in from the back. In the case of posterior lamellar keratoplasties, we put the transplant in with an air bubble in the posterior layer. It is not a difficult technique to undertake although it requires, just like any eye surgery, great precision and meticulousness.
It involves cutting out the whole pathological cornea and substituting it with a carved graft from the donor cornea. It is placed around the perimeter using fine sutures that are left in place for a few months or even years, until the join between the graft and the cornea is consolidated.
Surgical techniques have evolved over recent years and, nowadays, it is possible to selectively transplant the corneal layers affected based on the pathology of each patient. In keratoconuses, for example, it is the corneal stroma, the corneal collagen, which is affected, and only the collagen layer is transplanted. This is called a deep anterior lamellar keratoplasty. In endothelial dystrophies or endothelial degenerations, only the endothelial layear is affected and a posterior lamellar keratoplasty is undertaken.
There are various lamellar transplant techniques according to the layers being replaced:
The Femtosecond laser used to make the cut in the cornea has also made a noteworthy increase in the precision and safety of this technique.
In general, the results of transplants are good. The cornea is an eye tissue that is not vascularised, there are no veins or arteries reaching it, which is why the likelihood of an immune reaction or rejection is very low.
In low risk cases, the results are excellent in 95% of patients. As situations become more complex or if the cornea is already vascularised, the rejection percentage may increase.
In high risk cases, 50 or 60% of transplants may fail. Not only is rejection one of the main causes of failure, it is also one of the conditions that complicate the eye's situation, such as glaucoma or disorders of the eye's surface.
In the interview during consultation, the ophthalmologist usually informs the patient of the approximate prognosis of their specific case. Some patients need to use immunosuppressants to reduce their defence response and diminish the chances of rejection.
Frequently asked questions
It is performed in cases where there is a cornea disorder which causes the abnormal entrance of light inside the eye.
There is a risk of rejection with any transplant, however, as a normal cornea does not have any veins it therefore has a immunological privilege giving it a high rate of success. In some cases where the original pathology increases the risk of rejection, there are treatments that help us to guarantee the operation's success. Despite that, the best strategy for avoiding any type of complications is strict follow-up with the surgeon.