Refractive Surgery Pearls: Pre-operative Planning for IntraLase Enabled Keratoplasty (IEK)

Compared with trephination, IEK provides increased stability and faster healing.

By Sumit Garg, MD and Roger F. Steinert, MD

As an alternative to corneal transplant surgery with a standard trephine, we perform IntraLase enabled keratoplasty with the IntraLase femtosecond laser (Abbott Medical Optics, Inc., Santa Ana, California). During IEK, precisely shaped interlocking incisions are made in the patient’s diseased cornea and the donor tissue. There are several patterns of cuts available for the surgeon to choose from, including, “top-hat,” “Christmas tree,” “mushroom,” “zig-zag”, and others. We prefer the “zig-zag” cut [Figure 1].

Figure 1. zig-zag cut

Two advantages of transitioning from corneal transplantation to IEK are increased stability and faster healing. Particularly, the “zig-zag” shaped incision of IEK produces a sevenfold increase in resistance to wound leakage compared to standard trephination and aids in suture placement with less suture-induced astigmatism. (1) Likewise, these incisions appear to heal faster because of a greater surface area that fits like a “lock and key.”

During the learning curve, ideal patients for IEK include those with predominantly central pathology who have not undergone previous corneal surgery, such as patients with keratoconus, corneal edema, or central corneal scarring. After gaining some experience, you may expand your repertoire into re-grafts of conventional penetrating keratoplasty (as long as an adequate peripheral rim is present), or patients with minimal superficial vascularization. Cases for caution include those with dense peripheral scars or deep vascularization because incomplete cuts may result. It is prudent to conserve such patients until you build considerable experience with IEK. As a rule of thumb, if the case seems questionable, err on the side of trephination.

PRE-OPERATIVE ASSESSMENT

In addition to a comprehensive ophthalmic exam, two specific measurements are taken during the pre-operative examination. First, the maximum acceptable graft diameter is assessed using a slit-lamp beam. In the case of a re-graft, we measure not only the original transplant but also the peripheral rim. This allows ordering the correct precut tissue diameter from the eye bank. Currently, grafts are sized in terms of “zig-zag” “A (8 mm),” “B (8.5 mm),” or “C (9 mm).” Additionally, peripheral pachymetry is obtained during the pre-operative examination. Automated measurements with the Visante OCT (Carl Zeiss Meditec, Jena, Germany), Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany), or Orbscan (Bausch & Lomb, Rochester, New York) provide accurate peripheral readings.

DAY OF SURGERY

On the day of surgery, we then refer to the peripheral pachymetry to guide the depth of the posterior laser incision. Generally, the IntraLase laser is not located within the operating suite. For this reason, we advise a 70 micron posterior bridge for the “zig-zag” shaped incision. As mentioned earlier there are a variety of patterns possible depending on the surgeon’s preference. Additionally, the placement of the tissue bridge can also be customized. For example, during a “zig-zag” incision the laser parameters are a posterior side cut that advances from deep stroma to anterior stroma at a 30 degree toward the periphery. The posterior side cut intersects the second cut, which is a lamellar ring with a width of 0.5 mm at a depth of 320 micron from the anterior corneal surface. The ring cut advances from periphery toward the center. The lamellar incision then intersects the third incision, which is the anterior side cut that intersects the ring cut and advances toward the anterior corneal surface angled toward the periphery at a 30 degree setting. With respect to the “zig-zag” incision, leaving a 70 micron posterior bridge allows for safety, ease of cut completion into the anterior chamber with a super sharp blade, as well as a smooth anterior contour, maintaining a “lock and key” configuration, afforded by the femtosecond laser incision.

TEST THE PARAMETERS

The planning calculator and procedure simulator test parameters that validate the femtosecond laser cuts, ensuring they are the right ones to use. These tools are available from IntraLase/AMO to help you get started if you wish to create a custom shape. Most surgeons use a standard shape, however.

You can order precut tissue from the eye bank that is the same size, oversized, or even undersized. The size of the donor tissue will influence the final refractive outcome. For example, under sizing the donor in a myopic keratoconus patient will result in a flatter cornea. If the patient is hyperopic, you can influence the outcome by over sizing the donor thereby steepening the cornea and thereby decrease the hyperopia. It is important to start conservatively, using the same-size donor and host for initial cases. After you get a feel for the reaction of the incision and suturing patterns, you can then start manipulating with over- or under sizing the donor to influence the final refractive outcome. Generally, we recommend same size grafts for most patients.

CONCLUSION

Traditional corneal trephination creates two slightly mismatched shapes, one on the host and the other on the donor tissue. This difference often leads to optical degradation from irregular astigmatism and higher order aberrations that often plague corneal transplantation patients. The benefit to the IEK is that identical interlocking laser incisions are made on the donor and the host facilitating a “lock and key” configuration. Proper patient selection and pre-operative evaluation are important when beginning IEK. We feel that in the right patient, IEK affords several advantages over conventional PKP, which is why we suggest adding this technique to your surgical repertoire. Using the guidelines outlined in this article will assist you through the learning curve with IntraLase enabled keratoplasty.

Sumit Garg, MD, is a Clinical Instructor in Cataract, Refractive, and Corneal Surgery at the Gavin Herbert Eye Institute at the University of California, Irvine. Dr. Garg has no financial disclosures. Dr. Garg may be reached at tel: +1 949 824 4122; e-mail: gargs@uci.edu.

Roger F. Steinert, MD, is Chair Ophthalmology and Director of Cataract, Refractive, and Corneal Surgery at the Gavin Herbert Eye Institute at the University of California, Irvine. Dr. Steinert states that he is a consultant to Abbott Medical Optics, Inc. Dr. Steinert may be reached at tel: +1 949 824 4122; e-mail: roger@drsteinert.com.

References

1. PR Newswire Web site. Introducing Laser Corneal Transplantation – The Procedure's Greatest Advancement In 50 Years – With IntraLase-Enabled Keratoplasty. Available at: http://www.prnewswire.com/mnr/intralase/25939/. Accessed March 26, 2009.