Laser Assisted Procedures in Penetrating Keratoplasty: Femtosecond Laser Anvil-shaped Cuts and Laser Welding of the Surgical Wounds

The femtosecond laser is used to cut an anvil-shaped laser incision used in PK. This design has the purpose to create a more structurally stable and predictable wound configuration with the aim of a faster recovery of vision and higher optical quality, compared with the conventional blade trephination and the most common laser-cut patterns. The "anvil" profile is designed as described in the followings. Donor and recipient corneal trephination are performed using a 150 kHz FS laser (iFS150TM, IntralaseTM FS Laser, Abbott Medical Optics -AMO, Santa Ana, CA, USA). As concerned iFS150 settings, we refer to the following technical parameters: in the donor graft, the outer and inner diameters of the ring lamellar cut at 350 µm in depth were set at 8.5 mm and 6.6 mm, respectively; the anterior-side cut started with an angle of 135° at a diameter of 7.7 mm, while the straight posterior side cut diameter was 6.7 mm. In the recipient eye, the diameters were designed to be 0.2 mm shorter (8.3 mm outer diameter, 6.4 mm inner diameter, 7.5 mm anterior side cut and 6.5 mm posterior side cut). After completion of the trephination, the corneal button was gently lifted from the host and the donor graft was secured in place on the recipient bed by means of 10-0 nylon cardinal sutures, which were removed after the final 16-running 10-0 nylon suture was completed. A similar FS-laser cut procedure producing a 0.2 mm-narrower corneal bed -diameter is performed on the patient's recipient eye. After completion of the trephination, the corneal button is lifted gently from the host and the donor graft is secured into place with 10-0 nylon cardinal sutures, that are removed as a running 10-0 nylon suture is placed.

The particular "anvil" shape of the graft provides a larger contact surface in between donor and recipient cornea, which enables an effective application of the diode laser welding technique of corneal wounds we have previously set up in cataract and PK applications (Menabuoni et al. 2007, Rossi et al. 2008). This laser-assisted suturing technique is based on the photothermal activation of the stromal collagen, providing an immediate sealing of the surgical wound and a good stabilization of the graft. Once the donor graft was sutured in its final position, diode laser welding was performed. A sterile saturated water solution of 10% w/v Indocyanine Green (ICG) (Pulsion Medical System AG, Munich, Germany) was prepared and applied to the walls of the surgical wound at the donor-recipient interface. A mild photothermal effect was induced by means of a near infrared diode laser (Mod. WELD 800, El.En., Calenzano, FI, Italy) that emitted at 810 nm. The laser light was delivered through a 300-micron core diameter optical fiber that was mounted on a handpiece and used "as a pencil" by the surgeon under a surgical microscope. In a slow, continuous/fluid motion, the surgeon moved the fiber tip along the wound edge at a distance of 1.5 mm from the external surface of the cornea. The power radiation emitted was a 60 mW continuous wave, which resulted in an 8 W/cm2 power density on the tissue surface. The laser welding treatment time was set at 130s.

Thanks two the combine laser assisted procedures, the possible reduction of suture materials allows a faster and improved the healing process, with minimal inflammation and reaction. Thus the combination of FS laser trephination with the diode laser welding technique may provide extremely precise, and minimally invasive surgical procedures in PK.