Cornea is the clear, front part of the eye which focuses light into the eye and also protects the inner parts of the eye. Light passes through the cornea and reaches the retina resulting in vision. Thus, transparency of the cornea is essential for clear vision.
Among lay public, what may be incorrectly known as “eye transplantation” in fact means “corneal transplantation”.
This is a surgical procedure where a damaged and diseased cornea losing its transparency is replaced with a healthy donor corneal tissue.
Corneal transplantation requires expert skills of the ophthalmic surgeon.
Corneal transplant is the most successful type of organ/tissue transplantation. If the full thickness cornea is transplanted, this procedure is known as “penetrating keratoplasty”, whereas “lamellar keratoplasty” means only a layer of the cornea is replaced.
Several diseases may harm the transparency of the cornea. Infectious or genetic diseases, corneal trauma and unresolved corneal edema after cataract surgery or with some inherited diseases are among the leading causes affecting corneal transparency and disturbing vision.
The following are the list of the diseases for which a corneal transplantation may be needed:
The surgery can be performed under either local or general anesthesia.
The distorted or opacified cornea is removed by using specialized equipment and is replaced by healthy donor cornea which is sewn using ultrafine sutures with operating microscope. This is a precision surgery that requires sewing donor cornea with either 16-20 seperate sutures, a single continous suture or a combination of both methods. The total duration of surgical procedure is around 60 minutes which may be longer if other procedures should be performed concurrently.
Depending on the layer of corneal tissue involved, the type of corneal transplantation differs:
When the full thickness corneal tissue is replaced with the donor cornea as described above is known as penetrating keratoplasty.
If the innermost layer of cornea (endothelium) is intact, the outer part of cornea is replaced then the procedure is known as “deep anterior lamellar keratoplasty (DALK)”.
When corneal endothelium is diseased, then endothelial cell transplantation (DMEK) is performed.
During DALK operation, the outer part of the cornea including the epithelial and stromal parts which constitutes 85-90% of the entire corneal tissue is removed. But the endothelial layer is left in place. Since the transplanted donor cornea does not include endothelium, the rejection of the cornea is significantly decreased. Therefore, the duration of the usage of cortison eye drops may be shortened. The wound healing is faster and the sutures are removed within 6 months after the operation.
This procedure involves the replacement of the inner part of cornea, only including endothelium and Descemet membrane. This type of surgery is frequently performed for persisting corneal edema which may be a sequelae after cataract surgery or seen after certain ages in persons with inherited corneal diseases. Since the patients preserve the outer parts of their own cornea, they are more protected against trauma. The number of sutures used in operation is limited as compared to other types of corneal transplantation.
The transplanted cornea is obtained by a recently deceased person with no known diseases or any other conditions which may affect the survival of donor tissue or the health of the recipient patient. In Turkey, donor corneas are obtained from eye banks certified by the Health Ministry. For non-resident patients, the corneas are imported from abroad through registered agencies.
Since corneal tissue lacks any blood vessels, the cells causing rejection usually can not reach to transplanted cornea. Thus, the corneal transplant is relatively more successful compared to other organ transplants. Rejection is seen only 5-10% of cornea recipients which may be succesfully treated with early intervention. However, if the treatment is unsuccessful, the eye surgeon may decide to perform a re-transplantation. The patients should seek immediate consultation with an experienced opthalmologist if they experience pain, blurred vision, light sensitivity or redness in the transplanted eye.
Rejection may occur even after several years following transplantation. Therefore, regular, periodic follow-ups are essential after corneal transplantation.
The following problems may occur as a complication after corneal transplantation:
Most of the patients experience a significant improvement in their vision after corneal transplantation. This improvement is closely related with the condition of the eye before operation. In some patients, the vision may not improve immediately after transplantation, but may take a few weeks to months. During this period, vision may be improved by using glasses or contact lenses.
The follow-up after transplantation is usually performed at the 1st day, 1st week and the 1st month after surgery and every month thereafter.
Antibiotic and steroid eyedrops are given. A transparent eye cover to protect the transplanted cornea is used after operation. During the first couple of weeks patients may feel burning and stinging sensation and watering in the eye. Protecting the eye from trauma is extremely important. Particulary during the first year after transplantation, patients should be under close observation of an ophthalmologist and should meticulously apply their medications.
If the initial sutures are continous type, they are usually removed one year after the operation.
If single, separate sutures were used, the ophthalmologist may remove some of these periodically and may even replace some of them to correct the irregularities of the cornea thereby managing the astigmatism. As a consequence the patient’s vision will be improved.
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PROFESSOR YONCA AYDIN AKOVAOphthalmologist and Eye Surgeon
