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  • Corneal Grafting
    Corneal Grafting

Corneal Grafting

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). The graft has been removed 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.

Cornea transplant after one year of healing

Cornea transplant after one year of healing, two stitches are visible

Cornea transplant approximately one week after surgery

Cornea transplant approximately one week after surgery. Multiple light reflections indicate folds in the cornea, which later resolved.

Indications

Indications for corneal transplantation include the following:

  • Optical: To improve visual acuity by replacing the opaque or distorted host tissue by clear healthy donor tissue. The most common indication in this category is pseudophakic bullous keratopathy, followed by keratoconus, corneal degeneration, keratoglobus and dystrophy, as well as scarring due to keratitis and trauma.
  • Tectonic/reconstructive: To preserve corneal anatomy and integrity in patients with stromal thinning and descemetoceles, or to reconstruct the anatomy of the eye, e.g. after corneal perforation.
  • Therapeutic: To remove inflamed corneal tissue unresponsive to treatment by antibiotics or anti-virals.
  • Cosmetic: To improve the appearance of patients with corneal scars that have given a whitish or opaque hue to the cornea.

Pre-operative examination

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. The surgery only takes place when the best corresponding donor tissue is found. This can take weeks and months.

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.

Penetrating Keratoplasty

A trephine (a circular cutting device) is then placed over the cornea and is used by the surgeon to cut the host cornea, which removes a circular disc of the patient cornea. The trephine is then removed and the surgeon cuts a circular graft (a "button") from the donor cornea. Once this is done, the surgeon returns to the patient's eye and removes the host cornea.

The donor cornea is then brought into the surgical field and maneuvered into place with forceps. Once in place, the surgeon will fasten the cornea to the eye with a running stitch (as used in the upper image above) or a multiple interrupted stitches (as in the lower image). The surgeon then reforms the anterior chamber with a sterile solution injected by a cannula, then testing that it's watertight by placing a dye on the wound exterior.

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

This procedure consists in leaving just the patient's own Descemet membrane and endothelium, while transplanting approximately 95% of the cornea. The great advantage of this technique is the virtually "no rejection" post-op. The main disadvantage is that the visual acuity is not as sharp as it is with the full cornea transplantation penetrating keratoplasty). The final visual acuity is usually around 20/40.

Risks

While the cornea is avascular, there is still a potential for some blood loss, usually from suturing the metal ring to the sclera. Any blood loss is typically less than 2 ml (0.07 imp fl oz; 0.07 US fl oz).

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).

Graft failure can occur at any time after the cornea has been transplanted, even years or decades later. The causes can vary, though it is usually due to new injury or illness. Treatment can be either medical or surgical, depending on the individual case. An early, technical cause of failure, may be an excessively tight stitch cheesewiring through the sclera.

Prognosis

When the primary purpose of a cornea transplant is to improve visual acuity, the prognosis is dependent upon whether the rest of the eye is healthy. If it is, then it should be possible to recover normal vision.

Boston keratoprosthesis

The Boston keratoprosthesis is the most widely used synthetic cornea to date with over 900 procedures performed worldwide in 2008. The Boston KPro was developed at the Massachusetts Eye and Ear Infirmary under the leadership of Claes Dohlman, MD, PhD.

AlphaCor

In cases where there have been several graft failures or the risk for keratoplasty is high, synthetic corneas can substitute successfully for donor corneas. Such a device contains a peripheral skirt and a transparent central region.

AlphaCor is an FDA-approved type of synthetic cornea measuring 7.0 mm in diameter and 0.5 mm in thickness.

The main advantages of synthetic corneas are that they are biocompatible, and the network between the parts and the device prevents complications that could arise at their interface.

AlphaCor surgery is reserved for patients who have had traditional cornea transplants either fail repeatedly, reject due to autoimmune process or have a highly vascularized cornea that makes traditional cornea transplantation unsuitable.

Use of AlphaCor involved a two part procedure. First the AlphaCor disc is implanted under the tissue. Second, after healing many months later the membrane covering the lens of the disc is removed allowing that eye to see. Glasses will still be needed to optimize vision afterwards.

Osteo-Odonto-Keratoprosthesis

In a very rare and complex multi-step surgical procedure, employed to help the most disabled patients, a lamina of the patient's tooth is grafted into the eye, with an artificial lens installed in the transplanted piece.

Phototherapeutic keratectomy (PTK)

Diseases that only affect the surface of the cornea can be treated with an operation called phototherapeutic keratectomy. With the precision of an excimer laser and a modulating agent coating the eye, irregularities on the surface can be removed. However, in most of the cases where corneal transplantation is recommended, PTK would not be effective.

Intrastromal corneal ring segments

The implants manufactured under the trade name Intacs are the only patented intrastromal corneal implant that has US FDA approval and European CE Mark for both Myopia and Keratoconus.

With this procedure, the implants are placed in the stroma to reshape the cornea into a more natural shape. In mild myopia, this corrects a patients vision. In keratoconus, the goal is to reshape the cornea to where contact lens intolerant patients are able to achieve functional vision with contact lenses or glasses. Although, surgical procedure doesn’t carry a guarantee, one clinically proven benefit of Intacs is that they can be safely removed and the cornea returns to its pre-operative state. Future treatment options are not affected.

Contact lenses

In the early stages and up to the more advanced stages of keratoconus, contact lenses are often used to improve vision. Contact lenses improve visual acuity of the majority of the keratoconus patients. The majority of the patients need to use hard contact lenses. Only 10 to 20% will need cornea tranplantion during their lifetimes due to progression of the disease.

DSEK / DSAEK / DMEK

Endothelial keratoplasty (EK) has been introduced by Melles et al. in 1998. Today there are three forms of EK.

  • Deep Lamellar Endothelial Keratoplasty (DLEK) in which the posterior part of the recipient cornea is replaced by donor tissue.
  • Descemet's Stripping (Automated) Endothelial Keratoplasty (DSEK/DSAEK) in which the diseased Descemet's membrane is removed and replaced by a healthy donor posterior transplant. The transplant tissue can be prepared by a surgeon's hand or ordered already prepared for surgery. DSEK/DSAEK uses only a small incision that is either self-sealing or may be closed with a few sutures. The small incision offers several benefits over traditional methods of corneal transplant such as Penetrating Keratoplasty. Because the procedure is less invasive, DSAEK leaves the eye much stronger and less prone to injury than full-thickness transplants. Additionally, DSAEK has a more rapid rate of visual recovery.Vision is typically restored in one to six months rather than one to two years.
  • Descemet Membrane Endothelial Keratoplasty (DMEK)] is the most recent EK technique in which an isolated Descemet membrane is transplanted. The DMEK procedure combines the anatomical benefits of DSEK/DSAEK with visual rehabilitation to 20/40 or better in 90% of cases and 20/25 or better in 60% of cases within the first three months. In the UK (2010) the only surgeon offering DMEK procedure under the auspices of the National Health Service is Mr. Ewan Craig of the Royal Shrewsbury Hospital.

Stem cells

There is a bioengineering technique that uses stem cells to create corneas or part of corneas that can be transplanted into the eyes. Corneal stem cells are removed from a healthy cornea. They are collected and, through laboratory procedures, made into five to ten layers of cells that can be stitched into a patient’s eye. The stem cells are placed into the area where the damaged cornea tissue has been removed. This is a good alternative for those that cannot gain vision through regular cornea transplants. A new development in this field is use of bone marrow stem cells to regrow the cornea and its cells. This technique, which proved successful in mouse trials, would be of use to those suffering from inherited genetic degenerative conditions of the cornea, especially if other means like a transplant aren't feasible. It works better than a transplant because these stem cells keep their ability to differentiate and replicate, and so keep the disease from recurring, longer and better.

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