Corneal Transplantation

 

What is corneal transplantation?

The cornea is the central part of the front of the eye through which we see. Normally, the cornea is smooth and transparent. However, injury, disease or certain medical conditions can make it cloudy or difficult to see through. Sometimes this problem can be fixed by removing some or all of the cornea and replacing it with corneal tissue from an organ donor. This operation is called corneal transplantation.

Is it safe to receive donated corneal tissue?

It is safe to receive donated corneal tissue. The medical history of every organ donor is reviewed carefully, and blood tests are performed to check for infections prior to corneal transplantation. If there is any doubt about the safety of corneal transplantation, the donated tissues are used for medical research instead of being transplanted into a patient's eye.

Why do people need a corneal transplantation?

 The most common reasons for performing the operation are:

  • Injury to the eye. Sometimes an injury will damage the cornea so severely that it will not heal correctly. The cornea plays an important role in vision, so even a small injury to it can greatly reduce vision. The doctor might recommend a corneal transplant to improve vision or, in more serious injuries, a transplant might be the only way to close the wound in the eye.
  • Medical conditions. Some infections of the eye can cause damage to the cornea that will not heal. Bacterial infections (whether contact lenses-induced or not), Herpes virus infections, etc... There are also certain medical conditions that make the cornea very thin or cloudy, or cause other problems that can only be treated by replacing the cornea.
  • Corneal swelling. Some people experience corneal swelling and clouding after cataract surgery. This is known as pseudophakic bullous keratopathy and is a common reason for corneal transplantation. Other people have an inherent corneal disease called Fuch's dystrophy, whereby the cells of the back-surface of the cornea fail to function adequately due to decrease in number and viability, leading to a gradual swelling in corneal tissue and a loss in overall optical quality and transparency of the cornea.
  • Keratoconus. The cornea is thin and weak, and the normal pressure inside the eye makes the cornea bulge outward in a cone shape. This is called keratoconus, and it causes severe vision problems. If vision with glasses is not satisfactory, treatment modalities can include rigid gas permeable contact lenses ("hard lenses"), ring implant insertion (INTACS),  and corneal transplantation as a last resort.

     

    Are there any alternatives to corneal transplantation?

    Some diseases that only affect the surface of the cornea can be treated with laser. This operation is called phototherapeutic keratectomy (PTK). (PTK uses the same kind of laser that is used in laser vision correction, most commonly known as LASIK).

    How is a corneal transplantation performed?

    Full thickness corneal transplantation (Penetrating Keratoplasty)

    Corneal transplantation can be done under general anesthesia; that is, with the patient "asleep." Local anesthetic, in which the patient is awake but does not feel the procedure, also can be used.  A portion of the cornea is removed using scissors and a special instrument called a trephine, which works  like a tiny circular cookie-cutter. This leaves an opening in the patient's cornea. Other techniques make use of the femtosecond laser to perform the initial circular cut. A similarly sized trephine is used to cut a section from the donor cornea. This section of corneal tissue is placed into the opening in the patient's cornea and fastened with very small stitches. After surgery, it is important not to put any pressure on the eye. It is best not even to touch or rub anywhere near the eye, so the doctor might put a shield over it. Wearing glasses or sunglasses will also help protect the eye. The ophthalmologist will prescribe eye drops to help the eye heal and prevent infection. Those drops will be used for several months after a corneal transplant. Without these medications, the eye risks to have problems with the new corneal tissue, such as rejection. In general, vision is not expected to be really good before 4-6 months to a year after surgery.

    Endothelial corneal transplantation

          If the main problem is in the back part of the cornea (weak cell layer not pumping water out of the cornea), then an endothelial transplantion can be performed, instead of a full thickness corneal transplantation. The advantages are a less invasive surgery and quicker visual recovery. A cornea from a human donor is still needed. The donor cornea is sliced, and only the back part of the donor cornea is used. The patient's cornea is not cut, but its inner layer (endothelium) is stripped, and the back slice of the donor cornea, containing a healthy endothelium, is inserted into the patients eye and attached to the back side of the donor (recipient) cornea with the help of an air bubble, which has as a function to exert a constant upward pressure on the donor corneal tissue to adhere to the patient's cornea. The whole procedure is performed through a tiny corneal incision, and is usually performed under local anesthesia.

    What is the success rate of corneal transplantation?

    The majority of the corneal transplantations done in patients with keratoconus, corneal scars and most types of corneal disease are successful, albeit the highest reported success rate is with keratoconus patients. The operation is less successful in eyes with a corneal infection or severe injury such as a chemical burn. In a small number of cases, the new corneal tissue is rejected by the body even though the operation was successful and all medications were taken correctly.

    The best way to avoid problems after corneal transplantation is to follow the doctor's advice, including using all medications as recommended and keeping all follow-up appointments. At these appointments, the doctor will check your vision in the eye with the transplant. It is not unusual for that eye to have vision that is very different from the other eye. This difference can be very disturbing, but eyeglasses or contact lenses can improve the situation.

    Is there an alternative to donated corneal tissue?

    In special situations, like some types of chemical burns or repeatedly failed or rejected corneal transplantations, a special type of  synthetic transparent prosthesis can be accommodated in the center of the human cornea. Postoperative complications of such surgery are higher than the traditional donated tissue transplantations. The available prostheses are the AlphaCor and the Boston Kpro implants.