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IntraLase Enabled Keratoplasty Update_022407
Laser Revolutionises Corneal Transplants
Four techniques of corneal transplant are in frequent use today, the application thereof depending on the layer of the cornea which is affected and has to be replaced.
These techniques are:
Penetrating keratoplasty:
This procedure is the most established technique, and has been available for a number of years. This implies the removal of the entire central cornea, with the replacement thereof by donor tissue. This procedure is indicated in advanced cases of keratoconus, or when the scarring or disease process involves the entire thickness of the corneal stroma.
Fig 1 – 3: Schematic representation of a penetrating corneal transplant procedure.
It is, however, possible to only replace the affected layer of the cornea, with preservation of the recipient’s own tissue to minimize complications. These transplant procedures are termed “lamellar corneal transplants” and are the latest additions to corneal transplant surgery.
DSAEK Procedure (Descemet's Stripping Automated Endothelial Keratoplasty)
DSAEK is a new corneal graft transplant technique where the unhealthy, diseased, posterior portion of a patient's cornea is removed and replaced with healthy donor tissue obtained from the eye bank. Unlike conventional corneal transplant surgery known as penetrating keratoplasty (PKP), the DSAEK procedure utilises a much smaller surgical incision and requires fewer corneal sutures. This usually results in more rapid visual rehabilitation for the DSAEK patient and also better post-operative visual acuity.
Who is a candidate?
DSAEK is indicated for those patients who have corneal pathology located on the posterior aspect of their cornea known as the endothelial layer. When endothelial cells are healthy, they function as a "pump-leak system" to provide nourishment for the cornea. In other words, these cells allow nourishing fluid from inside the eye (aqueous humor) to leak into the cornea. After the corneal cells have been nourished, the cells pump the fluid out of the cornea. If the endothelial pump is compromised for any reason the cornea will over hydrate and become cloudy. This most commonly occurs in patients who have sustained trauma to the endothelial layer during complicated cataract surgery or patients who have an inherited disease of the corneal endothelium known as Fuchs' Endothelial Dystrophy. Such patients are good candidates for the DSAEK procedure. It is also indicated for patients with endothelial rejection and bullous keratopathy.
DSAEK Corneal Transplantation Procedure
The first part of the DSAEK procedure includes removal of the unhealthy, compromised endothelial cells and attached Descemet's membrane. The second part of the procedure involves replacing this unhealthy tissue with healthy cells from a donor cornea. The entire intra-operative procedure is performed in about 20 to 30 minutes.
Approximately 30 minutes before the DSAEK procedure the patient is sedated. The DSAEK procedure can be performed under local or topical anaesthetic. DSAEK is a microsurgical technique that is performed under a special operating microscope.
Preparation of the donor tissue has been greatly facilitated by the use of the microkeratome. The microkeratome has been used for decades in refractive surgery and is most commonly used today to cut the flap in LASIK surgery. The donor tissue for the corneal graft is machine cut rather than hand cut and has a smooth surface which enhances visual recovery.
When the procedure is completed, the small incision site is closed with two or three sutures (much less than with Penetrating Keratoplasty procedures) and the patient is sent home to return the next day for follow-up.
Post-op visual recovery varies depending on the severity of the corneal cloudiness prior to surgery, but is much faster than with Penetrating Keratoplasty (PKP) procedures. Most patients notice improvement in their vision during the first two weeks after surgery with continued improvement during the next four to six weeks. This recovery represents a dramatic improvement over the time required following conventional corneal transplant surgery (PKP), which usually takes six to twelve months.
Anterior Lamellar Keratoplasty (ALK)
Through this technique, only the superficial part of the corneal stroma is removed and replaced by a similar donor section. The advantages of this procedure include the fact that the surgery remains superficial with the result that the host’s endothelial cell layer is preserved. A smaller bulk of tissue is transplanted, which reduces the antigenic load, and hence the chances of rejection. This procedure is indicated if the superficial part of the cornea is the only part affected, thus negating the need for a penetrating corneal transplant. .
Deep anterior lamellar keratoplasty (DALK)
This technique is very similar to the ALK, except that the whole corneal stroma is replaced (only the corneal endothelium and the Descemet’s membrane is left in situ). This procedure is indicated if the whole cornea is affected except for the corneal endothelium and Descemet’s membrane.
