Safeguarding the Cornea

Keratoplasty via femto laser: a game-changer

New use delivers quicker visual rehabilitation, low levels of astigmatism and superior wound integrity.

By Karen Blum, Contributing Author

The surgeon’s ability to make precise tissue cuts­, let alone patients’ quicker, more even healing and their reduced risk of resulting astigmatism, are reasons some cornea surgeons say laser keratoplasty is superior to mechanical trephination.

“It’s a light year’s change in technology in terms of safety and precision,” says Martin Fox, MD, chief of refractive surgery at the Cornea and Refractive Surgery Practice of New York and of Clarity/TLC Refractive Services in West Orange, N.J.

Classical manual keratoplasty techniques employ a round trephine blade to create the outline for transplantation in the recipient and a same-size or slightly larger trephine in a tissue punch to create the donor tissue. “Inevitably there are huge inaccuracies between the shape of the recipient and the shape of the donor,” Dr. Fox says. “As a result, when one approximates the transplanted tissue into the recipient bed there are areas where sutures have to be tighter or looser depending on the size mismatch.” Frequently, patients have high degrees of irregular astigmatism and a prolonged recovery because no two areas along the graft-host interface heal equally. “The laser technique changes all that.”

A custom cut

Using a femtosecond laser to prepare donor and recipient tissue, surgeons can create a customized shaped cut, depending on patient’s morphology and pathology, says corneal surgeon Luca Menabuoni, with Nuovo Ospedale S. Stefano in Prato, Italy. Surgeons can dictate to an eye bank which shape to use or cut their own donor tissue. Then, like a final puzzle piece, the donor tissue approximates more easily into place, resulting in more even suture tension over the entire graft/host interface and less astigmatism for patients, Dr. Fox says.

Figure 1. A refined suture technique respecting laser cuts is necessary. Here, a desired bicurved needle pass is displayed, aligning anterior side and lamellar ring cuts. See Dr. Fox’s video at ophthalmologymanagement.com for more details.

In 2005 Francis W. Price, Jr., MD, president of Price Vision Group and the Cornea Research Foundation of America in Indianapolis, along with William “Buddy” Culbertson, MD, of Bascom Palmer Eye Institute at the University of Miami, and Roger Steinert, MD, of the University of California, Irvine, worked with the former IntraLase (now Advanced Medical Optics) to study the optimal-shaped cuts for corneal transplants. They started with top hat and mushroom configurations. Dr. Price says these were acceptable but didn’t lead to strong wound integrity. Then Steinert tried a zigzag incision. This cut had an angled posterior cut starting about 75 microns above Descemet’s membrane that connected to a lamellar cut and anterior side cut. The latter communicates with the corneal surface and breaks through the epithelium.

“A zigzag has some advantages that you don’t get with the others,” says Dr. Price. “A straight vertical incision doesn’t heal that strong in a cornea; that’s the problem we have with the trephines that you use with standard corneal transplants.” If a patient somehow suffers a trauma to the eye, even 10 or 15 years later, he says, it can easily separate and come open because the cornea, like a piece of plywood, is comprised of layers. “When you do the zigzag you’re going diagonally across the layers. For some reason they heal much more tightly. Part of that may be that the incisions are kind of stacked, because you have the zigzag back and forth on top of each other and that may induce some additional fibrosis.”

To patients, he explains that it’s similar to either nailing two boards together or having a tongue and groove-type attachment, which is a more secure joint. “That’s what we have with our transplants if we do the zigzag incision. So that’s been a real advance structurally, and it heals a little bit faster as well.” Other studies have shown the lamellar surface to be smoother with femtosecond laser cuts.¹

“Our goal was to use the laser to create multifactional shapes that use much more surface area and much more stability, with the theory that would lead to better optics, less astigmatism and healing more aptly,” says Dr. Steinert, director of the Gavin Herbert Eye Institute, the Irving H. Leopold Professor and Chair of Ophthalmology at the UC Irvine. “Now, five-year data is showing that all of that has occurred.”

Ordinarily after mechanical keratoplasty, patients can take up to a year to reach some point of visual rehabilitation, Dr. Fox says, “and in many instances all they can do is wear a hard contact lens because of the amount of irregularity generated in the cornea.” Following laser keratoplasty, patients could be rehabilitated in six to eight weeks, he says. It’s not unusual for patients to be seeing well within six weeks, with occasional outliers taking three months.²

In a recent consecutive series of 20 keratoconus patients treated with Intralase-enabled keratoplasty, he has documented that fully 75% were 20/25 in spectacles at eight weeks and at three months, the level of regular astigmatism averaged 2.5 diopters.

“With these kinds of satisfying outcomes, one can almost now consider laser keratoplasty as a refractive surgical procedure,” Dr. Fox says, “because the outcomes are that predictable. That’s a major jump in terms of the science and technology of corneal transplant surgery. It’s huge.”

Dr. Fox says some of his keratoconus patients who underwent laser keratoplasty in one eye, and scheduled to receive Intacs in the opposite eye have instead requested laser keratoplasty for the second eye because of the increased comfort and the quality of outcomes. “Your socks roll down and drop when you hear something like that, because a patient who’s had keratoplasty performed with manual techniques associated with a prolonged period of recovery will seldom savor going through a manual technique a second time.”

Figure 2. Zigzag pattern keratoplasty.

Femtosecond lasers can also be helpful in performing partial thickness corneal transplantation, such as endothelial transplant or anterior lamellar keratoplasty, Dr. Menabuoni says. “The laser welding procedure improves the healing process of the surgical wounds³ and can support suturing in penetrating keratoplasty,”⁴ he says. “It also can provide the only way to suture these tissues, located in inaccessible surgical sites like the endothelium.”

For deep anterior lamellar procedures, femtosecond zigzag incisions result in faster healing, stronger wound integrity, more regular corneal surfaces “and you don’t have to worry about a mismatch in thicknesses between the donor and the recipient,” Dr. Price says. “All in all it’s been just a huge improvement for patients.”

Dr. Fox also uses the femtosecond laser for lamellar transplantations as well as for the treatment of high astigmatism with paired arcuate incisions making use of a nomogram he has developed.

The downsides

There are some downsides to lasers, the experts say. For one, in the United States, the laser portion of surgery is not covered by insurance so it becomes an out-of-pocket expense for patients. That does pose a problem for some patients, Dr. Price says, although Dr. Fox says that his patients have no problems paying “when they learn how advanced this technology is compared to antiquated mechanical techniques.” In Europe, the National Health System covers laser keratoplasty, says Dr. Menabuoni.

Laser keratoplasty also requires the corneal surgeon to reorient to a revised suturing technique, Dr. Fox says: “I think part of the reason that laser keratoplasty really hasn’t caught on is that corneal surgeons haven’t modified their suturing techniques to take the best advantage of the tissue plane cuts that the laser delivers.”

The classic teaching of keratoplasty to corneal fellows dictates that sutures need to be very deep, to approximate the posterior corneal layers, he says, but with laser keratoplasty, “if you suture in that matter you lose the benefit completely.”

The zigzag

When using the zigzag pattern, sutures should be placed in the anterior one-half of the corneal donor and recipient, specifically at the junction of the anterior side cut and the lamellar ring cut, he says. “The other thing that I have changed is an approach to orienting the tissue planes precisely with replaceable working sutures before starting the final 10-0 nylon placement.” He uses a series of four black 8-0 silk sutures as cardinal sutures to make sure the tissue planes are aligned. They are placed at the 12, 3, 6, and 9 o’clock cardinal positions to approximate the donor and recipient tissue at the junction of the anterior side and lamellar ring cuts.

“This initial attention to accurate tissue plan apposition allows the surgeon to take advantage of the architecture created with laser cuts,” Dr. Fox says. He has posted a YouTube⁵ video demonstrating the highlights of his suturing technique.

“Many corneal surgeons have tried laser keratoplasty and abandoned it because they feel that it’s no advantage over mechanical,” Dr. Fox says. “I would say to them that the reason they feel that way is they’re just not suturing properly, and they’re not taking the time to make use of the benefit that the laser does provide.”

The use of the femtosecond laser as a precise corneal scalpel “is here to stay,” Dr. Fox says. “I honestly think that with the focused application of this technology, we’re going to be seeing that kind of happiness in our keratoplasty patients as well, which has been unheard of up until now.” OM

REFERENCES