Less is Better with the Corneal Transplant on Birmingham Medical News

Less is Better with the Corneal Transplant

By: Jane Ehrhardt

For over a hundred years, corneal transplants removed the entire thickness of the cornea. Now the procedure has gained such sophistication that ophthalmologists can retain some of the original tissue, and transplant only a few of the five layers.

Replacing fewer layers means less chance of rejection. “Why take normal tissue away if you don’t have to? Especially since immunological rejection is one of the major reasons for losing clarity,” says Roswell Pfister, MD, ophthalmologist and corneal specialist at Pfister Vision Correction Center. “These newer procedures also leave the cornea stronger because the full thickness of the cornea is not penetrated.”

Pfister now regularly performs one of the newer procedures, called deep anterior lamellar keratoplasty (DALK). It retains the two innermost layers of the patient’s cornea —Descemet's membrane and the endothelium.

Patients with keratoconus, macular, lattice or granular dystrophy are ideal candidates for DALK, since the abnormalities reside only in the upper corneal layers, or stroma. It can also better serve patients with scars that partially penetrate the cornea, or those with severe infections that might otherwise require a penetrating keratoplasty (PKP).

The procedure begins just like with a PKP, by making a round cut within one to two millimeters inside the edge of the cornea. However, the DALK incision cuts through only about 90% of the cornea’s thickness. The shallower incision may leave the eye able to endure hardier treatment. “At this point, things get very different from a PKP,” Pfister says.

Using the “Big Bubble” technique introduced in 2001 by Anwar and Teichmann, a hypodermic needle mounted on a syringe is pushed through the incision, deep in the corneal tissues but within the corneal lamellae, toward the center of the cornea. Air is injected, causing the stroma to have a frosted glass, whitish appearance, and separating the Descemet’s membrane from the corneal lamellae above.

With the air bubble between the two layers, a halo appears in the back part of the cornea. “Essentially, you’ve now isolated the tissue you want to keep from the tissue you want to remove, which is in front,” Pfister says.

The stroma is then cut into four sections and each quadrant is cut away from the incision edge. “While doing that, you’re dancing over a single membrane that is not more than 10 microns in thickness,” Pfister says. “It’s a very meticulous technique to arrive at this point. You’ve literally bared the Descemet’s membrane.”

“You don’t always get a big bubble,” Pfister says. He estimates that it works in more than60% of his cases. When the clear separation of the layers by air fails, the technique continues the same way but requires more careful, time-consuming and deeper dissection of the stroma, leaving behind only one to two percent of the stromal tissue. “You get excellent results either way.”

With the stroma removed, the donor’s cornea, now stripped of the two bottom layers and cut to size, is laid over the recipient’s exposed Descemet’s and sewn in place. Pfister temporarily secures the donor tissue with four sutures. Then he applies one continuous saw-tooth suture around the entire cornea transplant and removes the cardinal sutures. The continuous suture lies buried under the epithelium leaving the surface smooth and intact.

With the transplant complete, a circular ring of lights is projected onto the cornea surface to determine if the transplant is spherical. If the circle appears elliptical, a special spatula, called the Pfister Cincher, is slipped under the suture and the surgeon manipulates the suture until the elliptical image appears round. “Elliptical means astigmatism,” Pfister says. “Making it round by adjusting sutures removes astigmatism.”

Pfister created the spatula years ago, because he found that using forceps flattened and damaged the sutures, which could cause them to break prematurely. Using a spatula underneath the sutures alleviated that damage, while still allowing him to tighten a suture in one area and loosen in another, turning an ellipse into a sphere.

The DALK procedure takes approximately fifty minutes, about twenty minutes longer than a penetrating keratoplasty. “It takes longer than PKP because of its meticulous character,” Pfister says. “At any time, if the Descemet’s is too weak, it may break. Or when you’re trying to dissect — which can be very difficult — if the membrane splits, then you have to change over to a full PKP.”

Pfister cites excellent results with DALK. “I was surprised the visual results were as good as with PKP. But Pfister states that he did not switch to improve visual outcome, but because DALK reduced the chance of rejection and reduces the chance of traumatic rupture. “While a patient can reject the stroma, it’s usually less aggressive than with the endothelium and not likely to require a repeat transplant,” he says. “That’s extremely important. So these people have a better opportunity to keep that clear transplanted cornea for the rest of their lives.“