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Refractive Surgery | May 2009

Preoperative Planning for IEK

Compared with mechanical trephination, femtosecond laser keratoplasty provides increased stability and faster healing.

As an alternative to corneal transplant surgery with a standard mechanical trephine, we perform IntraLase enabled keratoplasty (IEK) 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.

Two byproducts of transitioning from corneal transplantation to IEK are increased stability and faster healing. The shaped incisions of IEK produce a sevenfold increase in strength compared with standard trephination and allow placement of fewer or looser sutures to secure the graft (Figures 1 and 2).1

During the learning curve, ideal patients for IEK include those with clear corneas who have not undergone previous corneal surgery, such as patients with keratoconus, corneal edema, or central corneal scarring. After initial experience, indications can be expanded to include regrafts—as long as an adequate peripheral rim is present—or minimal superficial vascularization.

Cases to be approached cautiously include those with dense scars or deep vascularization because incomplete cuts may result. 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.

Two separate measurement steps are taken during the preoperative examination. First, the maximum acceptable graft diameter is assessed using a slit-lamp beam. In the case of a regraft, measure not only the original transplant but also the peripheral rim. This will facilitate ordering precut tissue from the eye bank and determine what measurements will be used during surgery. The second set of measurements is for corneal thickness. 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.

On the day of surgery, we refer to ultrasound pachymetry as a supplemental measurement. However, we measure the area the laser will cut only in the periphery, not the center. The reason for this is that the laser must start in the posterior stroma, leaving a little bridge of tissue in one of three places to maintain a stable anterior chamber until the patient is moved to the operating room. The first option is to place the nonintersecting bridge at the intersection of the anterior sidecut and the ring lamellar cut. Alternatively, it can be made between the lamellar ring cut and the posterior sidecut. The final choice is to make the bridge at the posterior aspect of the posterior sidecut. In the latter, the procedure starts in the posterior stroma rather than at the anterior chamber.

The planning calculator and procedure simulator test parameters validate the femtosecond laser cuts, ensuring they are the right ones to use. After simulating the IEK, 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, undersizing the donor in a myopic keratoconus patient will result in a flatter cornea. If the patient is hyperopic, you can influence the outcome by oversizing the donor. 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 undersizing the donor to influence the final refractive outcome.

Corneal trephination creates two shapes, one on the diseased cornea and the other on the donor tissue. This difference often leads to optical issues that plague some corneal transplantation patients. The benefit of the IEK approach is that the same type of cut is made on the donor and the host (Figure 3). That is why I suggest starting this technique using the patient selection techniques outlined in this article to assist you through the learning curve.

Sumit Garg, MD, is a Clinical Instructor in Cataract, Refractive, and Corneal Surgery. Roger F. Steinert, MD, is the Chair of 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. They may be reached at tel: +1 949 824 4122; e-mail: gargs@uci.edu and roger@drsteinert.com.