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Corneal_transplant

Corneal Transplant

Corneal transplantation, also known as corneal grafting, is a surgical procedure where a damaged or diseased cornea is replaced by donated corneal tissue (the graft) in its entirety (penetrating keratoplasty) or in part (lamellar keratoplasty). (Keratoplasy is surgery to the cornea.) The graft is taken from a recently deceased individual with no known diseases or other factors that may affect the viability of the donated tissue or the health of the recipient.

The cornea is the transparent front part of the eye that covers the iris, pupil and anterior chamber. The surgical procedure is performed by ophthalmologists, physicians who specialize in eyes, and is often done on an outpatient basis. Donors can be of any age, as is shown in the case of Janis Babson, who donated her eyes at age 10. The corneal transplantation is performed when medicines, keratoconus conservative surgery and cross-linking cannot heal the cornea anymore.

Indications:

Indications for corneal transplantation include the following:

Diagnostic Tests:

In most instances, the patient will meet with their ophthalmologist for an examination in the weeks or months preceding the surgery. During the exam, the ophthalmologist will examine the eye and diagnose the condition. The doctor will then discuss the condition with the patient, including the different treatment options available. The doctor will also discuss the risks and benefits of the various options. If the patient elects to proceed with the surgery, the doctor will have the patient sign an informed consent form. The doctor might also perform a physical examination and order lab tests, such as blood work, X-rays, or an EKG.

Procedure:

On the day of the surgery, the patient arrives to either a hospital or an outpatient surgery center, where the procedure will be performed. The patient is given a brief physical examination by the surgical team and is taken to the operating room. In the OR, the patient lies down on an operating table and is either given general anesthesia, or local anesthesia and a sedative.

With anesthesia induced, the surgical team prepares the eye to be operated on and drapes the face around the eye. An eyelid speculum is placed to keep the lids open, and some lubrication is placed on the eye to prevent drying. In children, a metal ring is stitched to the sclera which will provide support of the sclera during the procedure.

Penetrating Keratoplasty

A trephine (a circular cutting device) is used by the surgeon to cut the donor cornea, which removes a circular disc of cornea. A second trephine is then used to remove a similar sized portion of the patient’s cornea. The donor tissue is then sewn in place with sutures.

Antibiotic eyedrops placed, the eye is patched, and the patient is taken to a recovery area while the effects of the anesthesia wear off. The patient typically goes home following this and sees the doctor the following day for the first post operative appointment.

Lamellar keratoplasty

Encompasses several techniques which selectively replace diseased layers of the cornea while leaving healthy layers in place. Advantage includes improved tectonic integrity of the eye. Disadvantages include the technically challenging nature of these procedures which replace portions of a structure only 500 µm thick, and reduced optical performance of the donor/recipient interface compared to full thickness keratoplasty.

Deep Anterior Lamellar Keratoplasty

In this procedure, the anterior layers of the central cornea are removed and replaced with donor tissue. Endothelial cells and Descemets membrane are left in place. This technique is used in cases of anterior corneal opacifications, scars, and ectatic diseases such as keratoconus.

Endothelial Keratoplasty

Replaces the patient’s endothelium with a transplanted disc of posterior stroma/ Descemets/ endothelium (DSEK) or Descemets/ endothelium (DMEK).

This relatively new procedure has revolutionized treatment of disorders of the innermost layer of the cornea (endothelium). Unlike a full thickness corneal transplant, the surgery can be performed with one or no sutures. Patients may recover functional vision in days to weeks, as opposed to up to a year with full thickness transplants.

During surgery the patient’s corneal endothelium is removed and replaced with donor tissue. With DSEK, the donor includes a thin layer of stroma, as well as endothelium, and is commonly 100–150 µm thick. With DMEK only the endothelium is transplanted. In the immediate post operative period the donor tissue is held in position with an air bubble placed inside the eye (the anterior chamber). The tissue self adheres in a short period and the air is adsorbed into the surrounding tissues.

Complications include displacement of the donor tissue requiring repositioning (‘refloating’). This is more common with DMEK than DSEK. Folds in the donor tissue may reduce the quality of vision requiring repair. Rejection of the donor tissue may require repeating the procedure. Gradual reduction in endothelial cell density over time can lead to loss of clarity and require repeating the procedure.

Patients with endothelial transplants frequently achieve best corrected vision in the 20/30 to 20/40 range, although some reach 20/20. Optical irregularity at the graft/host interface may limit vision below 20/20.

The surgery date and time will also be set, and the patient will be told where the surgery will take place. Within the United States, the supply of corneas is sufficient to meet the demand for surgery and research purposes. Therefore, unlike other tissues for transplantation, delays and shortages are not an issue.

Risks:

The risks are similar to other intraocular procedures, detachment or displacement of lamellar transplants.

There is also a risk of infection. Since the cornea has no blood vessels (it takes its nutrients from the aqueous humor) it heals much more slowly than a cut on the skin. While the wound is healing, it is possible that it might become infected by various microorganisms. This risk is minimized by antibiotic prophylaxis (using antibiotic eyedrops, even when no infection exists).

There is a risk of cornea rejection, which occurs in about 20% of cases.

Prognosis:

The prognosis for visual restoration and maintenance of ocular health with corneal transplants is generally very good. Risks for failure or guarded prognoses are multifactorial. The type of transplant, the disease state requiring the procedure, the health of the other parts of the recipient eye and even the health of the donor tissue may all confer a more or less favorable prognosis.

The majority of corneal transplants result in significant improvement in visual function for many years or a lifetime. In cases of rejection or transplant failure, the surgery generally can be repeated.

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