When is a corneal transplant required??
The cornea is the crystal clear, tear-wetted front part of the eye. Diseases of the cornea often lead to a loss of transparency, so that those affected see on the otherwise healthy eye only very bad. The cornea is the strongest refractive medium in the optical system of the human eye. Any change in the cornea, however small, can therefore have dramatic consequences.
Scars for inflammation or injury as well as progressive diseases such as keratoconus, which leads to thinning and conical deformation of the cornea of the eye, ophthalmologists can often treat only degenerative diseases of the cornea by a transplantation of healthy human tissue.
Sequence of a corneal transplant
In a cornea transplant, the ophthalmologist replaces the patient’s diseased corneal tissue with healthy tissue from a deceased organ donor. So-called corneal banks mediate suitable grafts.
Surgical techniques of corneal transplantation
Basically, two forms of transplantation can be distinguished: classic perforating keratoplasty (transplantation of all corneal layers) and lamellar keratoplasty (transplantation of selected layers). Lamellar techniques are gentler compared to perforating techniques. In addition, precious healthy corneal layers of the recipient can be preserved. However, these techniques are not always feasible or useful.
Classic perforating keratoplasty (pKP)
The most proven and most widely used form of corneal transplantation is classic perforating keratoplasty. The ophthalmologist replaces the central part of the diseased recipient cornea with a graft and sutures it. The threads used are thinner than a human hair and are among the finest used in medicine. The threads are left for up to a year and then gradually removed.
Lamellar keratoplasties
These techniques are currently experiencing a renaissance due to technical innovations and new operational techniques. Those skilled in the art distinguish the anterior (anterior) lamellar from the posterior (lamellar) transplantation.
Deep anterior lamellar keratoplasty (DALK)
This technique is only useful if the two inner layers of the cornea, the Descemet membrane and the precious corneal endothelium, are healthy. Ophthalmologists often use the DALK technique for keratoconus or scars of the anterior corneal layers. Here, only the anterior two-thirds of the cornea are affected by changes, so the surgeon does not need to fully open the eye. The risk during the procedure, the healing time and the risk of a rejection reaction are lower than with the pKP. The femtosecond laser can be used in addition to the DALK.
Posterior lamellar keratoplasty (DMEK)
In addition to the DALK, the technique is one of the most demanding but also the most gentle procedures in transplantation surgery. The graft consists of the two innermost layers, the Descemet membrane and the endothelium of the cornea. Eye surgeons use the procedure mainly for disorders of the corneal endothelium. The technique works in contrast to pKP and DALK without seams. The surgeon needs a bubble of air to position the transplant. If the transplant fails, a DMEK can be repeated. The option of pKP also remains.
Before keratoplasty surgery
Before surgery, the surgeon must first determine which parts of the cornea are affected by changes and which procedure is best for that patient. The decision to have a corneal transplant should be well considered, as it means an intensive and long connection to the ophthalmologist. The goal of transplantation is to improve the visual clarity of the cornea. Once this is done, vision-limiting refractive errors must be treated using intraocular lenses, contact lenses or glasses.
Sequence of corneal transplantation
The operation is performed on an outpatient basis under local anesthesia and sedation (twilight sleep) and lasts 90 to 120 minutes.
Classic perforating keratoplasty
With the scalpel or a femtosecond laser, the ophthalmologist prepares an approximately 8 millimeter diameter corneal disc from the donor tissue. Then he removes a similar sized slice on the receiver eye. He then sutures the remaining tissue of the recipient with the donor tissue.
Corneal transplantation with the femtosecond laser
Also in corneal transplants, doctors use this modern technology. They speak of two different tissues: the diseased corneal tissue of the patient (recipient) and the healthy tissue of the donor. Ophthalmologists use the femtosecond laser to prepare both tissues. The precision of this technology in the field of corneal transplantation is unsurpassed to this day. Patients also benefit from the procedure: eyesight and patient recover faster after surgery than with conventional procedures.
Lamellar keratoplasties
Deep anterior lamellar keratoplasty (DALK) In this technique, the eye surgeon uses a scalpel or femtosecond laser to make a vertical, non-penetrating, round incision (approximately 8 mm in diameter), preserving the healthy inner layers of the recipient’s cornea. By injecting air into the lower third of the cornea, he separates the healthy and diseased layers from each other. The donor tissue is similarly prepared by the physician to then suture the inserted graft to the recipient tissue.
Posterior lamellar keratoplasty (DMEK)
For the DMEK, the ophthalmologist first carefully strips the Descemet endothelium complex to be transplanted from the donor cornea. The graft has a thickness of only 30 microns, is extremely fragile and is used by the doctor without contact by means of fluid exchange in the eye of the recipient. Previously, the surgeon has removed the diseased inner corneal layers on the receiver eye. By means of an air bubble, he places the graft on the recipient tissue.
Risks of corneal transplantation
As with all eye surgery, the risk of infection is paramount. In transplants there is an additional risk of graft failure or rejection of foreign tissue. However, the corneal transplantation is one of the most successful tissue transplants in medicine, because the corneal tissue is not directly in contact with the blood supply and thus the immune system. A strong drug inhibition of the immune system is usually not necessary.
After keratoplasty surgery
After surgery, the eye surgeon applies a sterile bandage, which he removes the next day postoperatively. The first days and weeks after surgery, the eye may be more likely to be tears and reddened. Often there is a strong glare sensitivity and a foreign body sensation. Depending on the technique, the ophthalmologist will consider removing the sutures at the earliest after six months; Usually he only does that after one year. After healing and removal of the suture, in the next step, the doctor will look after the patient with improved refractive power and visual acuity.
Our specialists for this area
Dr. med. Detlev Breyer, dr. med. Hakan Kaymak, dr. med. Karsten Klabe Dusseldorf
Dr. med. Tobias Neuhann Munich
Dr. med. Thomas Pahlitzsch, Prof. dr. med. Carl Erb Berlin
Dr. med. Thilo Schimitzek Kempten
Dr. med. Wolfgang Lenz and colleagues Dillingen
Dr. med. Laszlo Kiraly Leipzig
Pallas Clinics Zurich
Dr. med. Mark Tomalla Duisburg
Dr. Volker Rasch Potsdam
Dr. med. Florian Kretz, dr. med. (University bud.) Matthias Gerl Ahaus / Rheine
Prof. Dr. med. Holzer, Prof. dr. med. Rabsil Weinheim
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