Corneal transplant and artificial cornea

What is the cornea? What is a corneal transplant?

Cornea; It is the transparent layer on the colored part in the front of the eye. It is the lens with the highest refractive power in the eye, which refracts the rays entering the eye to form a clear image in the visual center. The cornea, which has lost its transparency or deformed due to various diseases or trauma, can be replaced with a healthy cornea obtained from an eye bank, and the ability to see can be regained. This procedure is also called “corneal transplant”, “corneal transplantation” or “keratoplasty”. The success rate after corneal transplantation varies depending on the underlying disease requiring transplantation and other pathologies in the eye.

How common is the need for a corneal transplant?

When irreversible damage occurs to the cornea, the only treatment option is surgery, namely corneal transplantation. There are an estimated 10 million people worldwide who are blind from corneal causes.

Corneal transplantation is performed by replacing the diseased cornea with corneal tissue taken from a cadaver. However, there are difficulties in obtaining corneas from cadavers for transplantation, and many patients wait in the cornea for years. 1.5 million people worldwide become blind every year because cornea transplants cannot be performed.

What are the conditions that require corneal transplantation?

  • Severe deterioration of corneal shape without deterioration of corneal transparency (for example, keratoconus)
  • Deterioration of the transparency of the corneal layer
  • Spontaneous melting / perforation of the cornea due to rheumatic diseases in the body

Is it possible to reject the transplanted cornea?

As in every organ and tissue transplant, there is a risk of rejection in corneal transplant. Tissue rejection is an attempt by the body’s immune system to recognize tissue transplanted from a foreigner and try to get rid of it. This effort is manifested by clouding and vascularization in the new corneal tissue, the transplanted tissue does not disappear. Since the corneal tissue is avascular, the rejection rate is low (15-20%). Re-transplantation can be done to replace a rejected cornea, but the risk of rejection is even higher (up to 50%) in such patients. The success rate decreases in chemical injuries in which vascular structures are formed and stem cells are damaged in the cornea. If the rejection reaction has progressed and the cornea has lost its health, corneal transplant surgery may be required again. However, each previous corneal rejection increases the risk of rejection of the transplanted cornea. Artificial corneas (keratoprostheses) can be applied in patients who have a low chance of survival and preservation of the transparency of the transplanted cornea and have a high risk of rejection.

What are the developments in the field of artificial cornea? What is a Boston-type keratoprosthesis?

Since the first keratoprosthesis surgery was performed in 1855, a great deal of progress has been made in the field of keratoprostheses in the world and many different keratoprostheses have been developed. Boston type keratoprosthesis is the most widely used artificial cornea in the world today. This keratoprosthesis, whose development studies began in the 1960s, was approved by the Food and Drug Administration (FDA) in the USA in 1992 and has been used on patients since then. Its design has been improved over the years in order to improve the outcome of the surgery and it has been transferred to more than 3500 patients around the world to date. However, it has not been routinely applied in Turkey so far and has been applied to a small number of patients.

Since the central part of the Boston type keratoprosthesis is made of a transparent plastic material that does not stimulate the immune system, there is no risk of rejection by the body. In addition, due to the shape and design of keratoprostheses, the glasses numbers are very low or not at all after the surgery; and the best visual acuity is achieved in a very short time after surgery. Although keratoprosthesis surgery is very similar to standard corneal transplant surgery, postoperative follow-up is important and patients should be in close contact with their doctors. Postoperative life-long use of drops is required and patient compliance is very important in this regard.

Who may need artificial corneal surgery?

The success rate of corneal transplantation is 90% in developed countries and in eyes with a suitable environment for the transplanted cornea to survive. However, especially in patients with previous recurrent immunological corneal rejection, those with underlying rheumatic (eg, rheumatoid arthritis) or infectious (eg, herpes virus) disease, severe dry eye (eg, Sjögren’s syndrome), chemical burns and The success rate of corneal transplantation in patients who have been exposed to trauma and in patients with intraocular silicone oil due to previous retinal surgeries is seriously reduced. Artificial corneas (keratoprostheses) provide a new glimmer of hope in patients who have a low chance of survival and preservation of the transparency of the transplanted cornea.

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