BY MITCH LESLIE
A Stanford ophthalmologist has developed a more precise way to remove the cornea during corneal transplantation. The new technique, devised by assistant professor of ophthalmology Edward E. Manche, MD, uses an injection of gel to dislodge diseased corneal tissue so it can be more easily removed before a new cornea is fitted. If overlooked, remnants of this tissue can turn cloudy after surgery and cause blurred vision.
The outpatient operation takes less than an hour to perform and is easy for surgeons to learn, Manche said. "This procedure will greatly reduce the incidence of corneal graft rejection, which is the number one cause of failure in corneal transplant surgery," said Manche.
Patients may need a corneal transplant for several reasons. Injuries, infections and age-related thinning can damage the cornea, the clear, dome-shaped membrane at the front of the eye. Some people are born with badly warped corneas that produce distorted vision. Since glasses and contacts don't compensate for these defects, the only option is to replace the cornea with an unblemished one taken from a cadaver.
But both of the standard procedures for removing a damaged or diseased cornea have drawbacks, Manche said. One way is to cut out the entire cornea. However, the implanted replacement cornea is often rejected, or attacked by the immune system. Alternatively, surgeons can remove just the outer layer of the cornea, using an instrument that resembles a miniature cookie cutter. Although this option virtually eliminates the possibility of rejection, any stray bits of corneal tissue left behind can disrupt vision.
To simplify the removal of the outer layer, Manche decided to inject an inert gel into the edge of the cornea. Taking the path of least resistance, the gel slides into a natural "fault" in the cornea between the outer layer that he wants to remove and the inner layer he wants to leave in place. By separating these two layers, the gel makes it easier to see and cut away the upper layer. After the gel has been sucked up with a syringe, the transplant can be slipped into the opening.
Manche said that this technique combines the virtues of the two traditional methods. Because an inner layer of cornea remains in place, the transplant escapes attack from the immune system. And because all of the outer layer can be identified and removed, there is little chance that vision-disrupting fragments will be left behind.
Manche and colleagues Gary N. Holland, MD, and Robert K. Maloney, MD, presented preliminary results from four patients in the November issue of Archives of Ophthalmology. Holland is a professor of ophthalmology at UCLA, and Maloney is the director of the Maloney Vision Institute in Los Angeles. All four patients showed improved vision with no side effects. Manche said he has successfully performed another 10 surgeries since.
Carried out under local anesthetic and in sterile conditions, the surgery usually lasts less than an hour, after which the patient can go home. Vision usually takes two or three months to stabilize, after which patients must wear glasses or contact lenses to achieve sharp eyesight.
Health insurance covers the cost of
the surgery, Manche said. For more information, contact Barbara
Devlin at (650) 723-6995. SR