The Femtosecond Laser in Corneal Transplants

Precise incisions are greatly improving outcomes.

BY ROGER F. STEINERT, M.D.

The techniques and technology of penetrating keratoplasty have remained largely unchanged since the introduction of the operating microscope and 10-0 nylon suture in the early 1970s. Currently most transplants remain clear for a number of years, but commonly have large amounts of astigmatism and optical aberrations (formerly referred to as irregular astigmatism). As a result, many patients do not recover good visual function despite a clear transplant, and may be dependent on ill-fitting and uncomfortable rigid contact lenses to gain benefit from their surgery.

I have found that using a femtosecond laser to create and shape the incisions in the donor and patient corneas greatly improves the outcomes of corneal transplant procedures. This article will explain how laser-cut incisions result in faster recovery of vision, quicker healing, improved stability and a greater degree of patient comfort.

Why Use the Laser?

The goals of femtosecond laser penetrating keratoplasty are to:
► obtain excellent alignment of the anterior surface of the donor and host corneas
► improve the accuracy of rotational placement of the donor in the host
► reduce the necessity for excessive suture tension, speeding the recovery of stable and useful vision
► obtain a greater wound stability and strength, improving patient safety and enabling earlier suture removal when indicated.

The femtosecond laser can produce results that meet these objectives because it emits very short pulses of light. A femtosecond is just one-quadrillionth of a second. In 1 second, a pulse of light could travel around the equator of the earth seven times. Yet in a femtosecond, that pulse of light would only travel the width of a human hair.

By having a laser that gives such a short pulse of light, and also focusing it on a very tight spot, a special type of laser-tissue interaction occurs. Each laser pulse creates a tiny bubble of gas that will split apart a micron of tissue. The laser is able to cut tissue because it fires pulses extremely quickly (currently 60,000 pulses per second). By having a computer control the movement of the laser spots so that each spot is right next to the previous pulse, the total effect of millions of pulses can be an incision. The laser can be directed to create a virtually infinite variety of cut patterns.

The initial use of this laser technology was to create the corneal flaps for LASIK and approximately 400 of these lasers are already in place in the United States. With an upgrade of both software and the optical hardware, these lasers can also be used to perform corneal transplants.

Improving Incisions

Because of the exquisite control of the laser and the ability to create an almost infinite variety of patterns of pulses, the laser can create shapes of the incision in the donor cornea and the patient cornea. These shapes can create an inherently stable incision, so that the donor cornea lines up more predictably and stably with the rim of the patient's cornea.

The femtosecond laser has the potential to be the ultimate corneal incision device. It is controlled by computer software; therefore, a variety of incisions can be programmed. It offers the great advantage over manual incisions in that the laser is very precise, allowing the surgeon to perfectly match the donor and host tissue. This creates a corneal incision that is stable, predictable and secure much earlier following the transplant, allowing patients faster return to functional vision.

A variety of shapes are under exploration by surgeons. My preference is for a "zig-zag" shape for most patients. An image of the zig-zag shape using optical coherence tomography provides an optical cross-section that clearly shows excellent alignment of the cornea transplant at 3 months postop (Figure).

Figure. At 3 months postop, this corneal transplant performed with femtosecond laser incisions shows excellent alignment.

This is not a sutureless procedure. Currently, I use a 24-bite 10-0 nylon running suture unless the presence of inflammation or vascularization indicate the use of interrupted sutures. The use of the femtosecond laser to create incision patterns that fit together exceptionally well could lead, eventually, to fewer sutures being required, or possibly a combination of sutures and tissue glue.

Results Are Excellent

The early results in human surgery thus far match the promise shown in the laboratory investigations. Patients recover useful vision sooner and have less astigmatism than conventional transplants. Excellent BCVA, typically better than 20/30 in patients with normal retinal function, is common at 3 months postop. Most patients have less than 3 D of astigmatism. Some cases do need adjustment in the tension of the running suture.

A number of surgeons are learning the technique and upgrading their lasers to be able to perform this FDA-approved procedure. No complications or adverse reactions to the laser incision are known, and it is improbable that any issues will emerge. OM