Through the availability of improved technology, innovation is possible—and usually occurs in our never-ending quest to improve outcomes, efficiency, and cost-effectiveness. The ability of the IntraLase FS laser (IntraLase Corp., Irvine, California) to perform deeper cuts within the cornea, along with its user-definable software in the first iteration, has resulted in several geometric cut proposals for use during penetrating keratoplasty.

José I. Barraquer, MD, proposed the top hat geometrical shape, and Massimo Busin, MD, devised its mechanical method. IntraLase enabled keratoplasty (IEK) has made the process of creating this geometric shape relatively easy on both donor and host corneas. The cynic may ask, "Why bother with this complexity? What are its advantages?" In reality, IEK and its technology are only realistically afforded in practices that perform refractive surgery.

To date, problems with corneal transplantation include accurate trephination of the recipient cornea. A variety of mechanical devices now ensure that this step is reproducible (eg, Krumeich-guided trephine system [Rhein Medical, Inc., Tampa, Florida] and the Hanna trephine [Moria, Antony, France]). Although these trephines have succeeded at improving reproducibility, astigmatic and refractive outcomes are not significantly better. Problems with ultimate corneal shape, graft lifts or steps, sutures, and wound healing have also been major issues surrounding corneal transplantation. With newer technology, goals to minimize these problems are gradually being realized.

Now, a variety of geometric patterns are not only possible, but they are routinely used with IEK. Herein is a list of each pattern cut and its advantages.

Top hat. A laboratory study demonstrated improved corneal stability of the top hat configuration.¹ The theoretical advantage of this configuration—in addition to a good seal—is an increased posterior surface for endothelial disorders. The likelihood of graft lift is reduced, however, there is a theoretical possibility of posterior displacement of the graft. Furthermore, good anterior apposition is dependent on the donor cornea being of similar thickness peripherally to the host. This is unlikely to be exact, and as a result, the anterior surface will be compromised, increasing the potential for astigmatism compared with the mushroom (description below).

Mushroom. This is an alternate and opposite configuration to the top hat, where the large anterior lip ensures a self-sealing graft-host interface and improved astigmatism with absence of tilt. There are disadvantages, however, that include the possibility of the graft lifting off from pressure and the fact that less endothelial tissue is transplanted to the cornea. The last is of concern in patients who require penetrating keratoplasty for endothelial replacement.

Tongue and grooved. These configurations are an interesting concept based on engineering principles and include the zigzag, Christmas tree, and zig square. They are likely to be mechanically stronger, with better anterior apposition, provided that the anterior donor and recipient dimensions match.

Zigzag. This configuration was first proposed and performed by Roger Steinert, MD, of California. Its advantages include excellent apposition (with a larger anterior diameter), better corneal shape, reduced astigmatism, and rapid visual recovery. One disadvantage—found with all tongue and grooved patterns—is the fragility of the donor tongue, which I have found may tear during donor separation. Because the anterior dimensions and angles of both the donor and recipient are similarly created, the anterior apposition is almost an exact fit and independent of any disparity in thickness between the donor and recipient. Furthermore, the tapered anterior lip is similar to a LASIK flap and falls perfectly on the recipient without a visible step (Figure 1).

Christmas tree. This configuration, to my knowledge, has not yet been tried using IntraLase. Similar mechanical stability advantages are theoretically present, however, opposite to the zigzag and zig square (description below), the recipient-tapered lip faces centrally as opposed to peripherally. The advantages of a large anterior diameter and theoretical reduction in astigmatism are also lost. Nevertheless, this configuration adds more endothelium by increasing the posterior diameter. Similar with the zigzag, there is a possibility of tearing the cornea, and in this case, posterior recipient lip.

Zig square. I designed this geometric configuration, and it evolved from a combination of (1) Steinert's zigzag and (2) the mushroom shape. The anterior LASIK flap, like the tapered lip of the zig, provides excellent anterior apposition. Its square posterior donor lip is less likely to tear during donor separation, and the potential for a wider posterior diameter provides more endothelium when indicated. Early clinical outcomes have been good. Clear donors in an opaque host have confirmed the zig square configuration in vivo (Figure 2), and are further substantiated by Visante OCT images (Figure 3). Scanning electron microscopy of the donor button (Figure 4) is impressive and demonstrates accuracy of the IntraLase femtosecond cut. I have performed five IntraLase penetrating keratoplasties in total, one with the zigzag configuration and four with the zig square. At 6 months, all eyes had a BSCVA of 20/40 or better, and the average refractive cylinder was 3.20 D. All eyes also had noticeably more fibrous reaction. All sutures should be removed by 9 months.

As with other surgical techniques, there are several pearls to the zig square. The surgeon must take great care during donor and recipient separation following IntraLase femtosecond corneal trephination to avoid tearing the tongue or posterior lip. Although interrupted cardinal sutures must be used to ensure good apposition and graft centration, further interrupted sutures are counterproductive, as they force tissue to go in a particular direction rather than glide and fit into place. A loosely tied 16- to 20-bite running suture and removal of cardinals is better, as the donor graft fits into place. It is further assisted by the induced suture torque and graft rotation. Accurate placement of the needle is easy and guided by the junction of the zig square.

This technology enables us to be more innovative. Based on early data from European and US sites, there is a phenomenal benefit to our patients. As further options become available on this platform, undoubtedly more innovation will ensue, resulting in more creative corneal surgery.

We wish to acknowledge collaborators John Marshall, PhD, from St. Thomas' Hospital, in London, for performing scanning electron microscopy on corneal buttons. Add-itionally, present and past fellows of the Corneoplastic Unit and Eye Bank, Saj Khan FRCS, Omar Hakim FRCS(C), Samer Hamada FRCOphth, and Damian Lake FRCOphth, who collected data and acquired corneal images.

Sheraz M. Daya, MD, FACP, FACS, FRCS(Ed), is Director and Consultant, Corneoplastic Unit and Eyebank, at the Centre for Sight, Queen Victoria Hospital, in East Grinstead, UK. Dr. Daya states that he has received honoraria for speaking and performing live surgery on behalf on IntraLase Corp. Dr. Daya is the Co-Chief Medical Editor of CRST Europe. He may be reached at sdaya@centreforsight.com.

Marcela Espinosa, MD, is from the Centre for Sight, Queen Victoria Hospital, East Grinstead, UK. Dr. Espinosa states that she has no financial interest in the products or companies mentioned. She may be reached at marcela@centreforsight.com.

1. Ignacio TS, Nguyen TB, Chuck RS, et al. Top hat wound configuration for penetrating keratoplasty using the femtosecond Laser: A Laboratory Model. Cornea. 2006;25:336-340.