This month, the medical journal, Cornea, published an article looking at some trends in corneal transplantation (1). The authors reviewed billing claims data for more than 20,000 patients whose medical information contained the diagnosis code for keratoconus.
Overall, the authors found a downward trend in the number of corneal transplants performed over the last decade. They found that about 3% of these patients had undergone corneal transplant surgery; that number is lower than expected. The authors found that being male between the ages of 20 and 40 were among the most likely indicators of having undergone a transplant due to keratoconus. Several reasons were put forward as possible reasons for the decline in the number of transplants:
- Crosslinking has been available internationally for some time. Studies conducted in Europe found the numbers of corneal transplants decrease substantially as crosslinking became the standard of care. Even though this insurance data reflects U.S. patients prior to 2016, some proportion of these patients may have been treated abroad or participated in U.S.-based in clinical trials.
- There has also been substantial improvement in contact lens technology. ‘Hard to fit’ patients who might have undergone a transplant previously are increasingly managed with specialty contact lenses.
- Another possible explanation for the decreasing number of transplants may be that the transplant surgeries themselves are more successful and there are fewer repeat procedures.
Dr. Matthew Wade, MD, a cornea surgeon at the Gavin Herbert Eye Institute at UC-Irvine notes that advances in corneal transplant surgery have led to improved outcomes.
Penetrating Keratoplasty (PK or PKP) is the term that describes a ‘full thickness’ corneal transplant. First performed over a hundred years ago, the eye surgeon uses a device that resembles a round cookie cutter to cut the damaged cornea and remove it. A donor cornea is dropped in place and sutured.
Today, many surgeons are opting for a ‘partial thickness’ transplant called a deep anterior lamellar keratoplasty (DK, LK or DALK). While the cornea is no thicker than the side of a coin, it is actually made up of several layers of different types of cells. The layers most affected in keratoconus are the topmost layer (the layers closest to outside of the eye). So, like slicing a coin to make it even thinner, in DK, the cornea surgeon removes only the top layers of the diseased cornea, leaving the bottom part of the cornea (endothelium) in place. The doctor will then delicately separate the layers of the donor tissue and transplants only the top layer. Doctors find that transplants done in this manner have a shorter recovery period, lower risk of rejection and optimal post-operative vision.
“DK targets treatment to diseased tissue in a way that PK doesn’t”, observed Wade. He finds the procedure less invasive. “It makes sense to leave the healthy endothelium in place if possible.”
Despite the best efforts of your eye doctor to manage your keratoconus, for a small percentage of patients each year, the disease will advance to the point where useful vision cannot be obtained. In those cases, the doctor may recommend a corneal transplant.
The success rate for corneal transplant is over 80%. Occasionally, graft failure takes place and the donor tissue will need to be replaced in a new surgery. Graft rejection can take place anytime, from right after surgery to years, or even decades after the procedure was performed. In graft rejection, the body’s immune system tries to destroy the foreign tissue (even if it has been in place for some time). Wade noted that graft rejection does not automatically mean surgery to replace the cornea. “If caught in time, we have success stabilizing corneas and reversing rejection using steroids and antibiotic and anti-inflammatory medications.”
At the first signs of graft rejection, it is essential to contact your doctor to start treatment. Your eye surgeon will tell you exactly what to watch for. Common warning signs include vision loss, sensitivity to light and increased redness or pain.
1. Sarezky D, et al, “Trends in Corneal Transplantation in Keratoconus”, Cornea, 2016, Nov. 16, Epub ahead of print.
Dr. Matthew Wade, MD, is an Assistant Clinical Professor at the Gavin Herbert Eye Institute at UC-Irvine.
