Endothelial Keratoplasty (DSAEK and DMEK)

The human cornea is made up of five layers.

• ŸOuter – Epithelium and Bowman’s layer
• Middle – Stroma (consists of 90% of the total thickness)
• Inner – Descemet’s membrane and Endothelium

The endothelium is made up of a single layer of thousands of small cells. These cells sit on a thin strip of tissue called Descemet’s membrane. These endothelial cells are responsible for pumping fluid out of the cornea so it can remain clear and thin to provide good vision for the eye. If these cells stop working, the cornea fills up with fluid. It becomes swollen and cloudy, and causes blurry vision.

The endothelial cells can be lost due to

• ŸAging
• Inherited diseases (such as Fuchs’ Corneal Dystrophy)
• Eye Injury
• Previous eye surgery

If a critical number of endothelial cells are lost, the cornea becomes swollen and cloudy. Medical treatment is no longer helpful, and a corneal transplant operation is needed. The other corneal layers, the stroma and outer epithelium, are most often healthy. Many patients needing corneal transplant surgery have problems only with the endothelial cells.

What is Endothelial Keratoplasty?

Corneal transplantation or grafting, also called keratoplasty, is a surgical procedure performed to replace all or part of the damaged cornea with corneal tissue received from a healthy donor.

In the past, full thickness cornea transplantation (Penetrating Keratoplasty) was the only surgical treatment for all corneal diseases which required transplantation. Corneal transplantation has undergone a major advance over the past decade with the development of new procedures in the field of partial thickness cornea transplantation, in particular replacement of the inner corneal layers (Endothelial Keratoplasty).

In Endothelial Keratoplasty, the inner layers of your cornea will be removed without damaging the outer layers by making a small incision in the side of your eyeball. The donor graft will replace the removed corneal tissue.

Who are the best candidates for Endothelial Keratoplasty?

Endothelial Keratoplasty should be considered in patients with the following corneal diseases:

• Fuchs’ endothelial dystrophy
• Posterior polymorphous membrane dystrophy
• Congenital hereditary endothelial dystrophy
• Bullous keratopathy
• Iridocorneal endothelial (ICE) syndrome
• Failed penetrating or endothelial keratoplasty

What are the current techniques in Endothelial Keratoplasty?

At present, there are two types of Endothelial Keratoplasty, including:

• Descemet's Stripping Automated Endothelial Keratoplasty (DSAEK)
  
  This involves replacement of the inner corneal layers (Descemet’s membrane and Endothelium) along with a thin strip of the corneal stroma (corneal supporting tissue).

• Descemet’s Membrane Endothelial Keratoplasty (DMEK)
  
  This involves replacement of only the inner layer cells (Descemet’s membrane and Endothelium) of the cornea.

In both of these procedures, the replaced corneal tissues are held with the help of a temporary air bubble instead of stitches.

With DMEK, it is necessary for your ophthalmologist to separate the graft from the rest of the donor cornea, whereas the donor graft for DSAEK can be obtained directly from the Eye Bank.

Advantages of DSAEK

The major advantages of DSAEK (compared with PK) are:

• ŸFaster surgery
• Smaller wound (closer in size and location to a cataract surgery wound)
• More stable wound (less likely to break open from trauma)
• Minimal distortion to the cornea (postoperative astigmatism)
• Lower rejection risk
• Quicker recovery

Since only the thin inner layer of the cornea is replaced, over 90% of the patient’s own cornea remains behind. This adds to greater structural integrity and reduced chance of rejection.
There is a 10% risk of the graft becoming displaced within the first few days or weeks after surgery. This means the graft must be repositioned with a replacement air bubble in the eye.
If the DSEK operation fails, the procedure can be repeated with another button of donor endothelium.

Advantages of DMEK

Advantages of DMEK over DSAEK are:

• Better visual outcome
• Better quality of vision
• No significant refractive change
• Quicker recovery time
• Lowest chance of rejection

DMEK is a technically more challenging procedure. The preparation of the donor graft can be difficult as the inner layers of the cornea are extremely thin, and post-operatively there is a higher rate of graft detachment which requires rebubbling.

It is essential to note that DMEK is not for everyone. Some patients with significant corneal scarring or other serious eye conditions are not good candidates for DMEK. A DSAEK should be performed instead. Your ophthalmologist will evaluate your conditions before discussing the best treatment options for you.

What should I expect after DSAEK or DMEK?

• You will need to lie flat for one hour after the operation
• You will be examined by your ophthalmologist after the surgery before discharge home
• Mild discomfort and visible bleeding around the eye can be expected after the surgery
• You should never rub your operated eye after the surgery and no water exposure to the eye for at least 2 weeks.
• Your vision will not be very good initially when your eye is filled with the air bubble. It will improve gradually over a period of 4 weeks with DMEK and slightly longer with DSAEK
• It is critical that you don’t fly in an aeroplane after the operation until the gas bubble is completely gone (usually 7 to 10 days) and this is confirmed by your ophthalmologist
• You will be seen several days after the operation and again in one week to make sure the graft stays in position.
• It is recommended you take a minimum of two weeks off work, however you may discuss this with your ophthalmologist
• You will need to use eye drops for at least 12 months and in some cases indefinitely.