Appreciating Laser-enabled PK

Lamellar transplant strategies are the future, but full-thickness transplant with femto is excellent today.

BY YARON S. RABINOWITZ, MD

STANDARD FULL-THICKNESS CORNEA transplant has long been one of our most successful procedures, but the addition of the femtosecond laser has elevated our outcomes to a whole new level. The benefits for our patients are many and include reduced postoperative astigmatism and faster recovery of best potential vision. The experience of my colleagues and I reflect the course of this major technologic advance, and we’ve learned quite a bit along the way about how to maximize it.

IntraLase-enabled keratoplasty (IEK) allows us to tailor a transplant using a variety of incision configurations, the most popular being the zigzag, the top hat and the mushroom. These incisions are very different from the trephine-created straight-down cuts of manual penetrating keratoplasty (PK). Notably, they are self-sealing and due to their larger surface area, have much stronger wounds, which are less prone to perforation. With regard to postoperative astigmatism, IEK addresses many of the contributing factors, which include decentration of the host trephination, decentration of the host button, unevenly excised host cornea resulting in excess or deficient tissue in the graft-host interface, uneven wound healing from uneven wound apposition, uneven suturing of the wound, and disparity between the donor and host buttons.

We studied IEK with a zigzag incision versus standard PK in patients with keratoconus.¹ IEK was a more efficient procedure that resulted in a stronger wound and less postop astigmatism. At 12 months, the IEK group saw better overall. However, once all of the sutures were removed, even though astigmatism was lower in the IEK group, the difference between the two groups was not statistically significant, which was disappointing. We achieved an average postop astigmatism in the IEK eyes of 2.9D, but the range of 0.75D to 9.8D was somewhat bothersome. Based on those results, we decided to change our approach. By switching to a mushroom configuration, in which less posterior tissue is replaced (an ideal approach for keratoconus), we produced statistically significant better astigmatism results in the IEK group compared with the standard PK group.

As I mentioned, faster visual recovery is another major benefit of IEK. We have been able to achieve good results for keratoconus patients with manual PK, but in many cases, that involved post-PK ­astigmatic keratotomy (AK), compression sutures and LASIK. In one patient, for example, it was 6 months before I removed the sutures, 9 months before I performed AK, 12 months before the first LASIK procedure and 15 months before a second LASIK procedure. All in all, it took 18 months for him to reach his full visual potential. In contrast, I recently performed IEK in his fellow eye. The procedure took 35 minutes. Post-op day one his visual acuity was 20/200. At 6 weeks, earlier than normal, his sutures were removed and his acuity was 20/50. Within 2 to 3 months, he was seeing extremely well and was very functional with 20/40 vision (with a mild cataract) and had 1.7D of residual topographic astigmatism.

PK vs. Lamellar Keratoplasty

The shift from PK to lamellar keratoplasty for corneal transplant that has begun to take place is a positive and exciting development. These procedures work nicely, but in my experience, they are not yet delivering the quality of vision patients desire. Take for example another one of my IEK patients, for whom we achieved 20/20 uncorrected vision in one eye. He recently came to see me again because he wants to have IEK in his fellow eye, which had previously undergone lamellar keratoplasty in Europe. The graft in that eye looks beautiful, but his visual acuity is a poor 20/40 to 20/50, which for a young active patient is less than adequate. Based on the results of his first eye, he chose to have IEK done on this eye.

I do believe that lamellar transplants are the future, but we are not quite there at this point. There is a huge variation in patient outcomes depending on the surgeon’s skill and the interface in many instances is still a barrier to good vision.

I look forward to the time when we are able to apply the benefits of the femtosecond laser to lamellar procedures as we did with PK.

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