Synonym
Keratoplasty
Definition
Corneal transplantation is the transfer of parts or all of the cornea of a donor’s eye to a recipient’s eye. Corneal transplantation today is usually performed in its entire thickness. This procedure is also called penetrating keratoplasty.
The prerequisite is that the other functions of the eye that contribute to vision are preserved. In particular, retinal function, intraocular pressure and tear production must be normal. Corneal cells cannot be produced synthetically, i.e. in order to be able to implant a cornea in a recipient, a corneal donor is required.
In most cases, the cornea is taken from dead people. The prerequisite is that the endothelium of the donated cornea is intact and vital. This requires that the cornea be removed from the deceased in a timely manner.
For this reason, a removal time of 12-18 hours after death should be observed. The corneas of young donors are better suited for corneal transplantation than those of older donors because older corneas are often associated with a loss of endothelial cells. Corneal cells cannot be produced synthetically, i.e. to be able to transplant a cornea to a recipient, a corneal donor is required.
In most cases, the cornea is taken from the dead, provided that the endothelium of the donated cornea is intact and vital. This requires that the cornea be removed from the deceased in a timely manner. For this reason, a removal time of 12-18 hours after death should be observed.
The corneas of young donors are better suited for corneal transplantation than those of older donors because older corneas are often associated with a loss of endothelial cells. After removal, the cornea must be placed in an appropriate nutrient solution. This allows the survival time of the donor organ to be extended by a few days.
Whether a cornea is intact or not can be determined by the clouding of the cornea, among other things, because defective corneas are much cloudier than intact ones. The donor is examined for infectious diseases before the removal. An HIV infection/AIDS or hepatitis B or hepatitis C infection rules out corneal transplantation.
If a corneal transplant is considered, taking all factors into consideration, the cornea is removed with a surrounding strip of about 5 mm and placed in the culture medium, which consists of hyaluronic acid, chondroitin sulfate and an antibiotic. Only during the operation is the corneal slice cut out with a very thin knife. This instrument, also known as trephine, is able to cut very precise and smoothly defined shapes out of the cornea.
A distinction is made between motor-driven trephines and hand-guided trephines for corneal transplantation. Furthermore, there is the possibility to cut out the cornea with a laser (excimer laser). The diameter of the cut cornea is between 6.5 mm and 8 mm.
At the recipient, the cornea is cut out in the same size and the cornea is sewn in with a very thin thread. This usually has a thickness of about 30 micrometers. The suturing technique of a corneal transplantation varies depending on the surgeon.
So-called single-button sutures and continuous sutures can be made. The suture material is removed 12 months after the operation at the earliest. The time until the cornea has grown in depends on how well the transplanted cells are preserved.
It is also possible to transplant individual layers of the cornea. This is also called lamellar keratoplasty. Here, only the upper corneal layer is removed and inserted into the recipient.
The condition is that the cornea of the recipient is not completely destroyed and the endothelium is still intact and vital. The lamellar surgical procedure is technically more difficult and has more complications. A keratoplasty/corneal transplantation becomes necessary when large parts of the cornea have been destroyed.
In the vast majority of cases, the causes are traumatic. Burns caused by accidents at work or perforations make up the largest part of this. But also foreign bodies that are left in the eye for too long and thus scratch the cornea may in extreme cases make keratoplasty necessary.
Improperly processed or inserted contact lenses can also lead to corneal transplantation.Besides the traumatic reasons for corneal transplantation, infections and inflammation of the cornea are another reason for this procedure. If the infection is very severe or chronic (chronic keratitis, herpes zoster, infection of the eye), it may also be necessary to transplant the patient’s cornea. Rarely, it is necessary to transplant the cornea after eye surgery as a result of complications.
In laser therapy of the eye, which is used to correct defective vision, parts of the cornea are ablated with a laser to change the refractive power of the eye. Too much ablated cornea not only means that the tasks performed by the cornea can no longer be guaranteed, but also makes a complete corneal transplant necessary in rare individual cases. In case of only superficial injuries and resulting scars, a lamellar keratoplasty can be considered, since the cornea is only superficially injured.
In case of injuries even in deeper layers, a complete transplantation is necessary in any case. In the case of extreme injuries of the eye, such as injuries of the eye due to burns or perforations, the eye diagnosis by the observer is often already sufficient. In the case of smaller injuries and formed scars, however, the damage is not so easy to detect.
Here, the application of a fluorescent liquid, which is then illuminated with a blue light, helps. Scars and small injuries of the cornea will then shine yellow in the light of the slit lamp. Depending on the severity of the injured cornea and the depth of the injury, a corneal transplant is then indicated.
In addition to infections, wound healing disorders and bleeding during and after corneal transplantation, there is also the risk of a rejection reaction of the recipient to the donated cornea. The healing of implanted cornea depends on the immune defense/immune system of the recipient against the donated cornea. If the transplant is free of vessels, the probability of a rejection reaction after the cornea transplantation is reduced, since immune cells still present from the donor cannot enter the new organism of the recipient.
In the other case, the risks of a rejection reaction increase significantly. The reaction can be suppressed by the administration of Ciclospoprin A. Due to the drug suppression of the recipient’s immune system, it has been possible in recent years to increasingly transplant corneas with ingrown vessels without great risks.
In order to prevent a rejection reaction after corneal transplantation, tissue-competent typing can also be performed prior to the procedure, so that the recipient receives only corneal transplants of his own cell type (HLA specificity). However, a rejection reaction can never be ruled out. For this reason, in addition to the very careful operation, the patient’s follow-up treatment is absolutely necessary.
Regular check-ups can make a clear indication of an imminent transplant rejection. Patients who feel a foreign body in their eye after a transplant should visit an ophthalmologist within one day. A slit-lamp examination can immediately visualize corneal swelling, which could indicate that a transplant reaction has begun.
