Femtosecond Laser-Assisted Lamellar Keratoplasty

Lamellar keratoplasty reduces intraoperative complications, optimizes postoperative refraction, allows faster visual rehabilitation, and decreases the risk of graft rejection. Combining the advantages of lamellar keratoplasty with the surgical precision of a femtosecond laser enables us new surgical options. Femtosecond laser-assisted lamellar keratoplasty techniques include femtosecond laser-assisted anterior lamellar keratoplasty (FALK), femtosecond laser-assisted deep anterior lamellar keratoplasty (FDALK), and femtosecond laser-assisted endothelial keratoplasty (FLEK).

FALK is a new corneal transplantation technique used in patients with anterior stromal pathologic features such as superficial corneal scars and anterior stromal dystrophies. It is technically different from manual or microkeratome-assisted anterior lamellar keratoplasty in that the femtosecond laser is used to cut donor and recipient corneas with precise depth and side cut settings. The diameter and the thickness of the incisions are decided according to the depth of the stromal involvement demonstrated with anterior segment optical coherence tomography. The diameter of the donor lenticule is prepared to oversize the recipient bed by 0.1 mm. Depending on the donor tissue quality and edema, the thickness of the donor lenticule is increased up to 20%. The almost perfect match of donor and recipient corneas often eliminates the necessity of suturing in FALK. As a result, sutureless FALK provides faster visual recovery and less astigmatism and eliminates suture-related complications. In patients with dense corneal scarring, increasing laser bed energy levels and decreasing laser spot separation increases femtosecond laser cut quality. However, it is not advised to perform FALK in cases with severe corneal scars obscuring visualization of anterior segment structures. The surgeon also can perform phototherapeutic keratectomy for residual stromal bed scarring before donor lenticule placement in FALK.

Femtosecond laser-assisted deep anterior lamellar keratoplasty can be performed in patients with deep stromal scarring, keratoconus, and ectasia. With this technique, graft edges can be selected as vertical, mushroom, or zigzag shaped. The donor button is sutured over the residual stromal bed, which has a thickness of 70 to 100 μm. Femtosecond laser-assisted deep anterior lamellar keratoplasty can be combined with big-bubble and deep-hand techniques for further refinement of the residual stromal bed.

The femtosecond laser also can be used to prepare posterior lamellar donor disks for Descemet stripping automated endothelial keratoplasty (DSAEK). The use of the femtosecond laser for Descemet stripping automated endothelial keratoplasty may be limited by the poorer cut quality with deeper stromal cuts (Hurmeric V, et al. IOVS 2010;51:E-Abstract 1131). Microkeratomes result in smoother stromal surfaces in endothelial keratoplasty tissue donors. The clinical impact of these limitations are not known; however, the visual acuity after FLEK has been reported to be lower than that after conventional Descemet stripping automated endothelial keratoplasty. Adjustments in laser patterns and energies may improve cut quality in FLEK. New-generation high-frequency femtosecond laser platforms create corneal cuts with lower energy levels and higher pulse frequency. Further studies are required to understand cut quality and clinical performance of these platforms in deep stromal lamellar incisions and FLEK.

Femtosecond Laser-Assisted Penetrating Keratoplasty

The basic concept of cutting a donor disc to fit into a hole has never been changed in penetrating keratoplasty (PK). However, complete healing of the classic vertical PK wound takes an extended amount of time. Besides, suture removal has the risk of late wound dehiscence. In 2003, Busin introduced manually prepared lamellar wound configurations in PK with promising postoperative visual and refractive outcomes. Femtosecond laser technology improved this technique with more advanced wound designs. The most commonly used femtosecond laser-assisted wound shapes include top hat, half top hat, dovetail, mushroom, zigzag, and Christmas tree. Conventional 90-degree vertical trephination also can be performed with femtosecond lasers. However, the aforementioned advanced wound shapes maximize the surface area of the wound incision and improve fit and stability of the graft–host junction. As a result, femtosecond laser PK combines the excellent visual outcomes of PK with the wound-healing advantage of lamellar keratoplasty.

The diameter of the posterior surface of the donor can be adjusted in femtosecond laser PK according to different purposes. In patients with endothelial insufficiency, the top hat configuration provides a larger posterior surface, which increases the amount of endothelial cells transplanted. In patients with keratoconus, a mushroom configuration provides smaller posterior diameter to maximize retention of the host’s endothelium and minimize the possibility of graft rejection.

The top hat shape is reported to be the most mechanically stable wound configuration. The internal tamponade of the peripheral lamellar wound construction makes the surgical wound watertight. The sutures hold the donor tissue in place more than preventing wound leak. Because of this, in theory, fewer sutures can be used and suture removal can be performed earlier in femtosecond laser PK. Radial alignment marks named as orientation teeth and notches are another femtosecond laser advancement, which helps to facilitate the positioning of the donor button and the placement of the cardinal sutures in femtosecond laser PK.