Selective corneal transplantation is well and truly on its way to replacing conventional penetrating keratoplasty (PKP). Corneal surgeons have witnessed a phenomenal growth in the use of Descemet's stripping automated endothelial keratoplasty (DSAEK) in the past few years, with a total of 17,468 DSAEK procedures performed worldwide in 2008, up from only 6,027 in 2006.1 The cause for this dramatic increase lies in two areas: improved technology and availability of precut tissue. Anterior lamellar keratoplasty (ALK) has also become more popular and commonplace outside the United States; however, only 1,072 procedures were performed in 2008. In that same year, 13,131 PKPs were performed for corneal opacity and keratoconus—both indications for ALK.
Why has growth of ALK been so poor in the United States? There are a few factors, such as the technical skill and time required to perform lamellar keratoplasty as well as reimbursement issues. Deep anterior lamellar keratoplasty (DALK) can be difficult, and the learning curve is fairly steep. But when successful, there is no doubt that long-term results after DALK are better for patients, who are discharged without ever having to worry about corneal blindness from graft rejection.
The question is: Can femtosecond laser technology help accomplish safe and reproducible lamellar keratoplasty? The femtosecond laser is capable of performing highly precise incisions in the cornea, in both location and direction, and has been revolutionary in LASIK. The technology is increasingly applied to grafts for both lamellar and penetrating keratoplasty. Reproducibility of the cut is increased with this precision technology, and this theoretically should translate into better outcomes. Early reports support this claim.2
AN EVOLVING TECHNIQUE
Since 2004, my experience with femtosecond lamellar keratoplasty has been with the IntraLase platform (Abbot Medical Optics Inc., Santa Ana, California). Performing this procedure with femtosecond technology has been an iterative process, with small changes based on initial outcomes. The 15- and 30-kHz lasers were programmed to make lamellar cuts using a spiral pattern (Figure 1A); however, we found from direct observation of the tissue that this resulted in a more irregular surface than the raster mode (Figure 1B). We thus used the latter to perform lamellar grafts but were initially disappointed with visual outcomes, which were poorer than with a microkeratome for similar superficial ALKs.
Deep anterior lamellar grafts in particular were poor in terms of visual outcomes; we attributed this to surface irregularities. Often visible ridges were seen on both donor and recipient, probably the result of compression folds from flattening the cornea using the applanation cone on the device (Figure 2). We then avoided deeper grafts and, for superficial grafts (250 µm or less), progressively decreased the spot separation from 12 and 10 μm to as low as 5 µm. We also used excimer laser phototherapeutic keratectomy (PTK) to provide a smoother surface on both host and donor (Figure 3). These changes helped provide better visual outcomes.
COMBINING TECHNOLOGIES: DALK
Use of the femtosecond laser has been beneficial in PKP procedures that use geometric patterns or trephination, like the Steinert zigzag and our own zig square. With the more recent IntraLase iFS model, inverse cuts can be performed. This construction appears to provide better biomechanics (personal communication with John Marshall PhD, FRCPath, FRCOphth [Hon]) and can be used to produce a geometric trephination as shown in Figure 4. The remaining lamellar dissection, which can be reduced to as small as 6 mm, can be performed using a mechanical technique, assisted by injection of air (ie, big bubble) or viscodissection. A combination of the two provides the best of both worlds, a precise and biomechanically better geometric trephination with a deep but limited manual lamellar dissection at Descemet's membrane or in pre-Descemet's stroma. Furthermore, for keratoconus, the anterior lamellar portion can be programmed to be even wider, ensuring broader anterior stromal replacement to prevent long-term peripheral ectasia and reduce postoperative corneal astigmatism. Initial results in my first three cases are good; however longer-term follow-up is required to determine if this combination has any advantage.
Femtosecond technology has added a whole new dimension to corneal surgery and with the cooperation of manufacturers has allowed innovation to take place. Hopefully the reproducibility and biomechanical advantages of femtosecond lamellar keratoplasty, along with ease of use, will result in better outcomes and an increase in the number of lamellar grafts performed wherever femtosecond technology is available.
Sheraz M. Daya, MD, FACP, FACS, FRCS(Ed), FRCOphth, is Director and Consultant of Centre for Sight and the Corneoplastic Unit and Eyebank, Queen Victoria Hospital, East Grinstead, United Kingdom. Dr. Daya is the Chief Medical Editor of CRST Europe. He may be reached at e-mail: sdaya@centreforsight. com.