Corneal Transplantation and DSAEK

Indications for Corneal Transplantation

The human cornea is composed of five layers, the epithelial layer is the most superficial layer and lies on Bowman's membrane. The thickest layer is the stromal layer which makes up about 90% of the total corneal thickness. Descemet's membrane provides support for the innermost layer, the corneal endothelium. The endothelial cells are a single layer of cells that pump fluid out of the cornea. This pumping function is necessary for the cornea to remain clear and thin and provide good vision for the eye. If the pump cells should become dysfunctional, damaged, or destroyed, the cornea becomes swollen and cloudy, and this causes blurry vision.

Endothelial cells can be lost due to aging, inherited diseases (such as Fuchs’ dystrophy), trauma, or previous intraocular surgery. If a critical number of endothelial cells are lost the cornea becomes swollen and cloudy. Mild cases can be controlled with medical therapy (hypertonic saline - Muro 128), but more severe cases require a corneal transplant. The majority of patients requiring corneal transplant surgery have suffered significant endothelial cell loss.

Penetrating Keratoplasty

A penetrating keratoplasty (PKP) is full-thickness corneal transplant, and was first developed over 100 years ago. In this procedure, donor tissue is transplanted to replace a patient's central cornea. A corneal transplant is done for a variety of conditions that lead to poor vision. These include Fuchs' corneal dystrophy, bullous keratopathy, herpes keratitis, and sometimes ocular trauma.

Traditional corneal transplant surgery has about a 90% success rate, and the rate of rejection is only about 8%. Rejection episodes can often be controlled with topical steroid drops. Occasionally, there are problems with sutures which can come loose, cause infections, or cause astigmatism. The astigmatism after traditional corneal transplant surgery can be significant enough that eyeglasses alone won’t give adequate vision. These patients may ultimately require contact lenses or additional surgery to reduce or eliminate the astigmatism. Because the wound is full-thickenss and 360 degrees, the corneal transplant wound is not as strong as normal. It is at risk to rupture or break open from mild or incidental trauma, even several years after the surgery. Full visual recovery can take 6 to 12 months.

DSAEK

A DSAEK procedure is a partial-thickness corneal transplant that replaces only the endothelial layer. A thin piece of donor tissue containing only the endothelial cell layer is inserted onto the back surface of the patient’s cornea. This new technique appears to be a significant improvement over the standard operation. The surgery itself takes less time with an experienced surgeon, involves a smaller surgical incision, requires far fewer stitches, heals faster and more reliably, and the vision returns faster.

There are several advantages to the DSAEK operation compared to standard corneal transplant surgery. The wound is smaller and closer in size and location to a cataract surgery incision. The smaller wound is more stable and less likely to break open from trauma. Because the wound is smaller and requires far fewer sutures, there is very little postoperative astigmatism which can delay the visual recovery. The maximum return in vision takes only about 3 to 4 months following DSAEK. Since only the thin inner layer of the cornea is replaced, over 90% of the patient’s own cornea remains behind contributing to greater structural integrity and may reduce the incidence of rejection.

Only patients with endothelial cell problems are candidates for DSAEK. Patients with corneal scarring or other conditions will still require the full-thickness procedure. Since corneal specialists have only been performing DSAEK for a few years, there are no long-term follow-up studies. There is a risk of the thin button of endothelium becoming displaced within the first few days or weeks after surgery and requiring a return trip to the operating room to reposition it. If the DSAEK operation fails, the operation can be repeated with another button of donor endothelium. If the DSAEK fails, either after one or multiple attempts, a traditional corneal transplant operation can be performed.