Corneal Transplantation: Modern Techniques for Corneal Transplantation at the Eye Clinic

A corneal transplant involves the transplantation of a human cornea or parts of the cornea. For this procedure, the recipient with the condition requires an organ or tissue donation from a donor.

In medical terminology, it is called “keratoplasty.” A corneal transplant is a treatment for irreversible changes to the cornea, such as those resulting from severe inflammation or injury.

A corneal transplant can be performed under general anesthesia or local anesthesia. This depends on the type of keratoplasty being performed.

The eye perceives visual stimuli from the environment and transmits them to the brain. The brain processes this information and then reacts accordingly.

The cornea plays a vital role in enabling our eyes to perceive sharp images.

It refracts most of the light before it hits the retina. The brain then receives the transmitted signals.

The Structure of the Human Eye – The Cornea Curves Forward in Front of the Iris

The cornea forms the front part of the eye and merges into the conjunctiva. The cornea is clear, transparent tissue that contains no blood vessels.

It consists of six different layers of cells:

• Epithelial layer
• Bowman’s membrane
• Stroma
• Dua layer
• Descemet's membrane
• Endothelial cell layer

For the cornea to function properly, it must be moistened with tears. Since the cornea is a vital part of the visual system, any disruption can lead to severe visual impairments. If the cornea becomes cloudy, the eye does not absorb enough light and visual acuity decreases. In the worst case, blindness may result. Corneal clouding can develop over the course of a person’s life or be present from birth.

In some cases, corneal opacity can be treated with special contact lenses or through surgery. In cases of severe corneal damage or an incurable disease, a transplant can restore vision.

This is the case with advanced corneal dystrophies. In this condition, there is progressive corneal clouding, causing the cornea to lose its transparency.

Doctors perform a corneal transplant when the cornea exhibits irreversible changes that significantly impair vision.

These may include: 

• Scars resulting from severe corneal inflammation: These are often caused by soft contact lenses. 
• Degenerative diseases of the cornea associated with thinning and deformation (a condition known as keratoconus)
• Congenital corneal disorders

Figure 1: Severe inflammation of the cornea caused by soft contact lenses. This results in permanent clouding of the cornea, which leads to significant visual impairment and may, in the long term, require treatment with a corneal transplant.

The corneal changes described above result in progressive, irreversible vision loss. Depending on the severity of the loss of visual acuity, the ophthalmologist will determine whether a corneal transplant is indicated. 

The ophthalmologist can usually make the diagnosis by examining the eye with a slit lamp. Sometimes, a corneal topography (“map”) is also helpful in confirming the diagnosis.

A corneal transplant is recommended for the following conditions:

• Fuchs’ endothelial dystrophy (accumulation of water in the endothelial cell layer of the cornea)
• Bullous keratopathy (calcium deposits in the corneal endothelial cell layer)
• Keratoconus (progressive thinning and cone-shaped deformation of the cornea)
• Crumbly or lattice dystrophy (deposits in the epithelial layer of the cornea)
• Scars on the cornea (for example, following an infection)
• Eye injuries (for example, from sharp objects)
• Chemical burns to the eyes

If a corneal transplant is necessary, doctors must first find a suitable graft. To do this, they search the so-called corneal bank. This can take some time and involves certain challenges, as there are fewer grafts available than there are people who need a new cornea.

Since a corneal transplant involves the donation of human tissue or an organ, certain legal requirements must be met. For example, two doctors must independently and beyond a reasonable doubt confirm the donor’s brain death within a specific timeframe. To determine brain death, certain medical criteria must be met. Furthermore, the donor must have consented to tissue removal for a corneal transplant during their lifetime. 

This consent can be given through verbal statements, written declarations, or by means of an organ donor card. If no consent has been given, the donor’s next of kin may also provide consent if it aligns with the donor’s wishes.

Coordination of Donor and Recipient

Donor tissue can be harvested within 72 hours of the donor’s death. To do so, there must be no contraindications on the donor’s part, which is statistically the case for more than two-thirds of donors. 

These would include, for example, HIV or other infectious diseases. Other vision impairments such as cataracts or glaucoma, as well as the donor’s age, do not constitute contraindications.

During the procedure, medical professionals excise a corneoscleral disc (a disc consisting of the cornea and sclera) from the donor’s eye and remove it. Once harvested, the donor material can be stored in the cornea bank for up to four weeks. Coordination centers match the material with a suitable recipient on the waiting list. 

The potential recipient is then notified by their treating physician. For the corneal transplant itself, the recipient visits an appropriate clinic.

During the surgery, the patient receives either local anesthesia or general anesthesia. Doctors remove the cornea either completely or partially from the eye.

After the diseased corneal tissue is removed, the recipient receives the donor tissue, which doctors suture to the remaining cornea. Depending on the type of corneal disease, as well as the location and severity of the corneal changes, different methods of corneal transplantation are possible.

There are essentially two main procedures used here:

• Perforating keratoplasty or
• Lamellar keratoplasty

In lamellar keratoplasty, experts distinguish between posterior and anterior lamellar keratoplasty. In cases of deep opacities, they perform a classic corneal transplant involving all layers (perforating keratoplasty). 

In this procedure, doctors completely open the recipient’s eye by excising a central disc from the center of the cornea. They then excise a disc of the same size from the donor cornea and suture it into the recipient’s eye (Figure 2). 

The surgery is performed under a microscope. For conditions affecting the anterior or posterior layers of the cornea, lamellar corneal transplants are used. In this procedure, part of the patient’s own cornea is preserved. This generally allows for faster healing with a lower risk of rejection.

Figure 2: Eye following a corneal transplant. Two very thin, continuous, star-shaped, counter-rotating corneal sutures are visible. These must remain in the eye for several months until the condition has stabilized.

After removal, doctors insert the new donor cornea and suture it in place. They trim the cornea beforehand so that it fits precisely into the patient’s eye. The sutures are not removed until several months later, as injuries to the eye take a long time to heal. Only after this period can doctors determine whether the transplant was successful.

• Perforating Keratoplasty

In perforating keratoplasty, doctors remove the cornea using a special device. This procedure is called trepanation. They remove a circular piece of the cornea from the eye. They then insert the donor cornea, which has been precisely tailored to fit. They attach it to the remaining cornea using fine sutures. 

The surgeon can either place two sutures in a star pattern or use individually knotted sutures. Which of the two techniques is used depends on the specific circumstances of the surgery. 

Perforating keratoplasty is the most commonly performed transplant worldwide. Consequently, the level of knowledge and experience in this field is very high. Furthermore, the graft used is very small, which reduces the risk of a rejection reaction.

• Posterior lamellar keratoplasty

Posterior lamellar keratoplasty is also known as an inner-layer transplant. It is used when the endothelial layer of the cornea is diseased. 

To remove the damaged tissue, surgeons make circular incisions in the damaged endothelial layer and Descemet’s membrane and then peel them away. They roll up the corresponding portion of the donor cornea and insert it through a tiny lateral incision. 

Once inside the eye, it unfolds, where an air bubble presses it into the correct position. To ensure this, the patient must lie on their back for 24 hours after the surgery. One advantage of this method is the short healing time, as no sutures are required. The patient can see well again after about three months.

• Anterior lamellar keratoplasty

This is also known as an outer-layer transplant. It is essentially the opposite of an inner-layer transplant. 

In this procedure, doctors separate and remove the remaining corneal layers from the Descemet’s membrane and the endothelial layer. They then replace these layers with a graft. 

Here, they secure the donor tissue back in place with sutures. As with penetrating keratoplasty, they use either two or a single suture. Because the endothelial layer is preserved, the risk of rejection is greatly minimized.

A transplant can always trigger a rejection reaction in the body. The body recognizes the graft as a foreign body and initiates defensive measures. This causes the immune system to attack the cornea. 

In this case, the cornea may become cloudy again. A rejection reaction usually manifests within the first five years after surgery. 

Symptoms include:

• Watery or red eyes 
• Deterioration of vision

Affected individuals should consult their treating physician immediately so that appropriate measures can be taken.

Overall, the risk of rejection is lower than with transplants of other organs. The new transplant may also become diseased again. If clouding recurs, only another transplant can provide a solution. This carries the same risks and has the same chances of success as the previous transplant. 

Furthermore, penetrating keratoplasty can lead to chronic endothelial loss. In this condition, the cell density in the endothelial layer continues to decrease. A follow-up keratoplasty is then necessary 15 to 20 years after the initial surgery.

The healing process after a corneal transplant can take weeks to months, depending on the type of surgery. 

After a penetrating keratoplasty, the corneal sutures must remain in place for up to a year or longer. The patient must also use eye drops long-term. During this time, the refractive power may still change, so it is not yet possible to prescribe glasses. In addition, the sutures can cause severe astigmatism, which limits vision and makes prescribing glasses more difficult. 

Laser treatment to reduce astigmatism using an excimer laser (“refractive surgery”) can be appropriate and successful in some cases. In individual cases, patients achieve 100 percent visual acuity with an intact retina. However, visual acuity is often between 40 and 80 percent.

In some patients, a rejection reaction may occur over time. In such cases, the cornea becomes cloudy and ceases to function. 

The risk of rejection is higher if:

• The recipient’s cornea is heavily vascularized prior to surgery 
• It is a repeat corneal transplant

After a corneal transplant, patients must attend regular (daily to every other day) follow-up appointments with an ophthalmologist.

Corneal transplants are usually performed on an inpatient basis at a hospital. There, close monitoring (e.g., to ensure the wound is intact) is guaranteed. Over time, the intervals between checkups become longer (initially weekly, later monthly). In addition to regularly applying eye drops and, if necessary, taking medication, it may be advisable to wear glasses with side shields at first. 

After corneal transplantation, the patient must protect their eye from foreign bodies or minor injuries. Initially, the patient often does not notice these because the recipient’s nerve fibers are not yet present in the donor tissue. These nerve fibers are important for sensation and the ability to detect foreign bodies.

It takes several months for the recipient’s new nerve fibers to grow into the donor tissue. An eyeglass prescription to improve visual acuity is often not possible until several months have passed.

• Medications After a Corneal Transplant

After a corneal transplant, the patient must use eye drops several times a day for an extended period (months to years), and initially even hourly.

These are corticosteroid eye drops, along with antibiotics initially. In addition, the patient should regularly use artificial tears. 

For high-risk surgeries with an increased risk of rejection, patients are also given tablets that suppress the body’s immune response (immunosuppressants). They must take these for several months following the corneal transplant as well.

• Exercise After a Corneal Transplant

The patient should avoid contact sports, as a transplanted cornea is significantly less stable initially than an eye that has not undergone surgery. 

In the long term, the ability to participate in sports depends on the findings and the type of corneal transplant. You should discuss this individually with your treating ophthalmologist.

An ophthalmic surgeon performs corneal transplants. After completing medical school, an ophthalmic surgeon undergoes a 5-year residency in the field. Most corneal transplant specialists also undergo intensive continuing education in the field of ophthalmic surgery.

The conclusion regarding corneal transplantation is that modern procedures, such as the endothelial technique on the Descemet’s membrane, can significantly improve visual acuity and vision. In this procedure, diseased corneal tissue is replaced with high-quality donor tissue, resulting in a new cornea that is once again transparent. Depending on the diagnosis, either the entire cornea or only a portion of it is transplanted and carefully sutured in place. Corneal transplantation is an effective treatment, particularly for corneal diseases or corneal opacities.

In lamellar procedures, specific layers of the cornea—such as the stroma or the epithelium—are selectively replaced, thereby reducing the risk of rejection compared to other organ transplants. The transplanted donor tissue must heal properly to ensure that vision and visual acuity remain stable in the long term. In some cases, laser techniques are used as a supplement to further improve cloudiness or astigmatism.

The operated eye requires a careful healing process that can extend over several months, although initial improvements are often visible just weeks after surgery. Regular follow-up visits with an ophthalmologist are important for early detection of potential complications. Most patients benefit significantly from the procedure, although in rare cases alternatives such as a keratoprosthesis may be necessary.

Overall, corneal transplantation demonstrates that, in cases of corneal disease or following an illness or injury, the cornea can be replaced to improve visual acuity. Concomitant conditions such as cataracts can also be addressed. The success rate is high when the corneal transplant is performed and follow-up care is consistently provided. Many patients who need a new cornea thus achieve a lasting improvement in their vision.

What is a corneal transplant?

A corneal transplant is a surgical procedure in which diseased corneal tissue is replaced with healthy donor tissue. It is performed when the cornea is severely damaged.

When is a corneal transplant necessary?

A corneal transplant is necessary for conditions such as keratoconus, scarring, or corneal opacity. Surgery may also be required following an infection.

How is the surgery performed?

During a corneal transplant, the diseased tissue is removed and replaced with a donor cornea. Depending on the method used, either individual layers of the cornea or the entire cornea are transplanted.

What are the risks?

As with any transplant, there is a risk of infection or rejection. Regular follow-up visits with an ophthalmologist are therefore important.

How long does healing take?

The healing process can take several months. Eye drops support healing and help prevent rejection.