10 Femtosecond Laser–Assisted Keratoplasty: Penetrating with Different Cut Profiles
This chapter presents different femtosecond laser cut profiles in femtosecond laser–assisted penetrating keratoplasty (FLAK) for various indications, as well as each profile’s descriptions, advantages, and disadvantages. It also presents general FLAK indications, advantages and disadvantages, preoperative evaluation methods, donor and recipient preparation steps, and differences between partial and complete cuts. All cut patterns presented in this chapter allow precise and customized graft configuration resulting in faster healing and earlier suture removal compared to the traditional PK. Although still there is no technique that can achieve sutureless corneal wound, the recently developed lock-and-key cut pattern, which is a combination of top-hat and mushroom cut patterns, promises superior advantages with its intrinsic mechanical stability.
Keywords: penetrating keratoplasty, femtosecond laser, femtosecond laser–assisted penetrating keratoplasty, femtosecond laser cut profiles, wound configuration
Penetrating keratoplasty (PK) is the surgical replacement of the entire thickness of host cornea with a donor cornea. Since 1905, 1 it has been the most common surgical technique performed in patients with decreased visual acuity secondary to corneal opacity, corneal thinning or perforation, and infectious foci resistant to medical therapy. Although PK can provide excellent clinical results for patients with significant visual loss from corneal disease, there are some regular, undesirable outcomes from the procedure. Healing of the classic vertical PK wound usually takes at least 1 year. Also, regular and irregular astigmatism can result in many patients due to imprecise trephination of donor tissue as well as imperfect alignment and suturing of the donor and host tissues. Moreover, in up to 4% of cases, suture removal has been shown to cause late wound dehiscence, even when done more than 1 year after surgery.
Throughout the years, surgeons have altered the methodology and approach to PK in an effort to reduce tissue distortion and minimize postoperative refractive errors. Specifically, surgeons have adopted various suture strategies, suction methods, tissue preservation techniques, viscosurgical devices, and combined surgeries in an effort to improve outcomes. In 1921, Carrell and Eberling described a straight (square) graft configuration, and in 1930s, Castroviejo demonstrated a variety of customized hand trephination patterns. In 1950, Franceschetti and Doret introduced multilevel stepped corneal incisions and described mushroom graft for improving donor to host alignment and wound stability. Later, Barraquer described a series of patterns involving circular grafts in order to achieve better wound approximation for a larger contact area, which resulted in a more hermetic closure of the anterior chamber, a reduced number of sutures, and a reduced endothelial surface and graft volume. In 1964, Barraquer described a two-level keratoplasty with a stepping graft, a mushroom-shaped graft, or posterior two-level graft. In 2003, Busin performed a modified PK with a lamellar configuration of the surgical wound using an artificial anterior chamber that allowed complete suture removal by 3 months postoperatively, promising a larger posterior diameter and reduced postoperative astigmatism. 1
The most recent progression in PK has come with the utilization of femtosecond (FS) laser technology. Femtosecond laser–assisted keratoplasty (FLAK) techniques allow for advanced wound designs; donor and host corneas can be cut in customized sizes and shapes to achieve a better graft–host fit. 2, 3 FLAK cut patterns have been shown to create watertight wound closure, allowing for more stable wound healing. Moreover, FLAK may allow for earlier suture removal and faster visual rehabilitation.
10.1.1 Femtosecond Laser–Assisted Penetrating Keratoplasty
The FS laser has been used successfully in variety of corneal procedures, including laser in situ keratomileusis, the creation of channels for intracorneal rings, and the preparation of donor and host tissue in anterior lamellar keratoplasty. Although this technology is currently most associated with lamellar corneal transplantation (Descemet’s stripping endothelial keratoplasty, deep anterior lamellar keratoplasty), the FS laser also has been shown to have many advantages for full-thickness transplantations as well.
Although FS PK can be used for the same indications as manual PK, it has its strengths and weaknesses.
Indications for FLAK
Corneal edema: Chronic or associated with scarring.
Deep stromal scars: Infectious, traumatic, or related to corneal hydrops.
Active infectious keratitis recalcitrant to medical therapy.
Immunologic keratitis, including prior transplant rejection or failure.
Severe corneal ectasia or perforations smaller than 3 mm. 6
General Advantages of FLAK
The shape of the corneal graft and the diameter of the posterior surface of the donor can be adjusted according to the type of disease or opacity to maximize the area of contact between donor button and recipient.
Cuts are at a precise depth, which is consistent, programmable, and reproducible with limited damage to surrounding tissues.
Less induced astigmatism.
Reduced the incidence of folds in the Descemet membrane.
Improved maintenance of endothelial cell counts.
Enhanced and expedite symmetric wound healing.
Earlier suture removal.
Radial alignment marks, called “orientation teeth and notches,” help facilitate the positioning of the donor button and the placement of the cardinal sutures.
The internal tamponade of the peripheral lamellar wound construction makes the surgical wound watertight.
Improves short- and long-term post-PK visual recovery with early suture removal.
Induces less trauma to donor tissue
Therefore, FS laser PKP combines the excellent visual outcomes of PK with the wound-healing advantage of lamellar keratoplasty.
General Disadvantages (or Contraindications) of FLAK
FLAK cannot be performed in eyes with conditions preventing proper laser docking, such as the following:
Severe ocular surface irregularity.
Elevated glaucoma filtering bleb or glaucoma shunt implant.
Small orbits or extremely narrow palpebral fissures.
Corneal perforations larger than 3 mm, which can result in extrusion of intraocular contents and expulsive hemorrhage (controversial) due to the intraocular pressure (IOP) rise produced by docking the suction ring.
FLAK is relatively contraindicated in the following:
Eyes with prior PK or globe trauma because of the risk of corneal/globe rupture.
Severe peripheral corneal neovascularization due to risk of graft rejection or failure.
Additional time requirements and logistical problems.
10.1.2 Femtosecond Laser Platforms
IntraLase (Abbott Medical Optics, Santa Ana, California, United States).
WaveLight (Alcon Laboratories Inc., Ft Worth, Texas, United States).
VisuMax (Carl Zeiss Meditec, Jena, Germany).
Technolas/Femtec (20/10 Perfect Vision, Heidelberg, Germany).
Femto LDV (Ziemer Ophthalmic Systems AG, Port, Switzerland).
10.1.3 Preoperative Examinations
Complete ophthalmic examination including potential visual acuity.
Complete systemic workup including serology and renal and liver function to reduce the risk of graft rejection.
Measure central and peripheral corneal thickness with an anterior segment optical coherence tomography (AS-OCT) to determine the FS laser cut settings (▶ Fig. 10.1).
Use the topography for the diagnosis of underlying pathology.
Fig. 10.1 Anterior segment optical coherence tomography; femtosecond laser cut settings.
10.1.4 Surgical Procedure
Donor Cornea Preparation and Trephination
The corneoscleral rim is mounted on an artificial anterior chamber in order to stabilize the tissue.
A pachymeter is used to measure the corneal thickness of the donor graft, which is needed to set the posterior depth cut on the laser settings.
A caliper is used to obtain the white-to-white measurement and to determine the diameter of the cornea that will be cut by the laser.
A marking pen is used to mark the center of the cornea for the perfect centration of the laser treatment zone (▶ Fig. 10.2).
Trephination can be performed using one of the various cutting profiles with one of the FS laser platforms (▶ Fig. 10.3).
Then the corneal button can be lifted easily with a Sinskey hook or other blunt or semisharp instrument (▶ Fig. 10.4).
The donor cornea is placed on the host cornea and is secured in place with sutures (▶ Fig. 10.5).
Fig. 10.3 Donor cut by femtosecond laser.
Fig. 10.4 Corneal button lifting with a Sinskey hook.
Fig. 10.5 Donor cornea suturing.
Recipient Cornea Preparation and Trephination
Topical anesthesia is administered.
The same instruments (a pachymeter, a caliper, and a marking pen) are used as for donor trephination; these are crucial to determine the FS laser settings that will perform recipient cuts.
A corneal suction ring can be placed over the globe and sclera and is centered on the limbus to achieve fixation of the eye.
The laser cone is lowered or the bed is raised depending on the laser being used while carefully observing for image centration during the docking (▶ Fig. 10.6).
The treatment zone on the screen can be adjusted to center it properly.
Recipient cornea cuts can be performed with one of various profiles according to the settings used for donor trephination (▶ Fig. 10.7).
The tissues can be easily separated with a Sinskey hook or other blunt or semisharp instrument once the patient transfers to the operating room.
Fig. 10.6 Image centration during the docking.