Purpose
To describe a new laser-assisted penetrating keratoplasty technique combining a femtosecond anvil-like trephination pattern with the laser welding procedure.
Design
Cohort prospective study with 1 year of follow-up (June 2011 through January 2013).
Methods
This study was performed at Misericordia e Dolce Public Hospital, Prato, Italy. Twenty-four eyes of 22 patients underwent penetrating keratoplasty: 4 had granular dystrophy, 12 had keratoconus in its final stages, 3 had post-herpetic leukoma, and 5 had corneal scars. A femtosecond laser was used to create anvil-profiled cuts in donor and recipient corneas. Diode laser welding was performed, supporting standard suturing. All patients were evaluated for corrected distance visual acuity, pachymetry, manifest astigmatism, and endothelial cell density after 1, 3, 6, and 12 months.
Results
Mean ± standard deviation postoperative corrected visual acuity was 0.48 ± 0.23 logarithm of the minimal angle of resolution (logMAR), 0.30 ± 0.18 logMAR, 0.18 ± 0.13 logMAR, and 0.13 ± 0.16 logMAR at 1, 3, 6, and 12 months, respectively. At the same follow-up times, mean pachymetry was 537 ± 57 μm, 533 ± 74 μm, 528 ± 72 μm, and 529 ± 58 μm, respectively; and mean endothelial cell density was 1945 ± 371 cells/mm 2 , 1881 ± 410 cells/mm 2 , 1781 ± 401 cells/mm 2 , and 1730 ± 376 cells/mm 2 , respectively. Mean manifest and topographic postoperative astigmatism were: 3.6 ± 2.5 diopters (D) and 4.65 ± 2.57 D at 1 month, 2.93 ± 2.34 D and 4.79 ± 2.85 D at 3 months, 2.82 ± 1.75 D and 3.44 ± 2.28 D at 6 months, and 2.08 ± 1.25 D and 2.73 ± 2.01 D at 12 months, respectively. All surgical operations were successful and without intraoperative complications.
Conclusions
The use of the anvil trephination profile was effective for performing laser-assisted penetrating keratoplasty. The large donor–recipient interface enables the laser welding procedure and good preservation of the recipient’s endothelial cell pool.
Application of femtosecond laser technology has brought about great advances in the field of corneal surgery. It can achieve precise tissue resection by means of ultra-short laser pulses in the subpicosecond range of duration. A solid-state femtosecond laser emits light in the near-infrared range, where the corneal tissue has very good transmission. The spot size of commercially available femtosecond lasers is adjustable to a few microns. It thus performs controlled intrastromal photodisruption, which results in minimally invasive laser surgery. The first applications of this technology were limited to the creation of corneal flaps in laser in situ keratomileusis procedures. Further advances in software and hardware technology, however, made it possible to create vertical and lamellar corneal incisions at precise depths, designing a large variety of shapes and angulations and minimal collateral tissue injury.
The first femtosecond laser platform to accomplish full-thickness corneal cuts was the IntraLase (IntraLase Femtosecond Laser; Abbott Medical Optics, Irvine, California, USA), which since 2005 has been equipped with IntraLase-Enabled Keratoplasty software for performing penetrating keratoplasty (PK). Since then, various femtosecond laser platforms have been developed to create stable full-thickness PK wounds.
Various incision patterns for PK have been described in the literature, including top hat, mushroom, Christmas tree, and zigzag types. With regard to mechanical strength, all of these wound configurations create a wider surface area at the interface between the donor and host corneal tissues, thus resulting in enhanced biomechanical stability of the graft, as compared with the traditional joint created in manual PK. The healing process in femtosecond laser-assisted PK is improved because this technique overcomes typical problems of conventional PK in terms of optical distortion and visual outcomes, such as misalignment between the anterior surface of the donor and that of the host, rotational displacement, excess and uneven suture tension, and postoperative slow and uniform wound healing.
The laser-welding procedure was proposed as a substitute for or in addition to standard suturing in corneal surgery. It is based on the photothermal activation of stromal collagen : the near-infrared light emitted by a diode laser is absorbed within the stroma by means of a suitable chromophore (indocyanine green) that has previously been applied to stain the tissue to be welded. The laser energy is absorbed by the stained stroma in depth at the cut site and is converted into a controlled heating effect, thus inducing a reorganization of the collagen between the donor and recipient tissues and the creation of fibril interdigitation on cooling. It has been demonstrated experimentally that the laser welding technique induces a mild temperature effect by heating the tissue at a temperature within the range of 50 to 60°C, that is, less than the threshold of collagen fibril denaturation, but high enough to induce a breakage in interfibrillar bridges (such as proteoglycan chains). During the cooling phase, new bridges are formed among the collagen fibers of the cut edges, and interwoven fibrils are observed at the weld site. This mild photothermal process provides an immediate sealing effect at the wound site, where it prevents postoperative inflammation and improves the healing process.
In this article, we describe the clinical outcome of laser-assisted PK using the combination of the femtosecond laser to trephine the host and donor graft in an anvil-shaped profile and the diode laser to weld the surgical wound. The anvil profile was designed for the purpose of creating a more structurally stable and predictable wound configuration to achieve a faster recovery of vision and higher optical quality when compared with conventional blade trephination and other more common laser-cut patterns. Moreover, this shape provides a wide contact surface between the donor and recipient corneas, allowing for an effective application of the laser-welding procedure.
Methods
Patient Selection
The study and data accumulation were in conformity with all state laws and the study adhered to the tenets of the Declaration of Helsinki. The study was conducted with the prospective approval of the Ethics Committee of the “Misericordia e Dolce” public hospital (study location, Italy; study identifier in the clinical trials database, MIL-PO-001). All patients were fully informed regarding the procedures and signed informed consent statements. This prospective study examined 24 eyes of 22 consecutive patients who were candidates for full-thickness keratoplasty. The ages of the involved patients ranged from 16 to 75 years (average age, 42.9 ± 19.7 years) and the male-to-female ratio was 3:1. All surgical operations and follow-up observations were performed at the “Misericordia e Dolce” public hospital in Prato, Italy. Among the 24 eyes that underwent PK, 4 had granular dystrophy (16.7%), 12 had keratoconus in its final stages (50%), 3 had post-herpetic leukoma (12.5%), and 5 corneal scar (20.8%). Preoperative examination showed 1 case of glaucoma, 1 case of slight amblyopia, and 1 case of cataract, all included in the study group. All procedures were performed by the same surgeon (L.M.), and all patients underwent general anesthesia.
Femtosecond Laser Trephination Procedure
The corneoscleral rim of the donor graft was secured to the artificial anterior chamber (Coronet, Network Medical Products Ltd.; Coronet House, Ripon, North Yorkshire, UK), and the intracameral pressure was maintained by the use of a syringe connected to the artificial chamber through the 3-way connector and was filled with Carry-C solution (Alchimia, Ponte San Nicolò, Padua, Italy). The pressure was tested manually by the surgeon, being crucial to guarantee a correct implementation of the femtosecond laser cut. Finally, the center of the cornea was marked with a felt-tip pen. After applanation of the donor cornea, graft trephination was performed using a 150-kHz femtosecond laser (iFS150, Intralase FS Laser; Abbott Medical Optics, Santa Ana, California, USA). A particular trephination profile, called the anvil, was drawn on both the donor and the recipient eyes, as shown in Figure 1 . 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 degrees at a diameter of 7.7 mm, whereas 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 lifted gently 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.
Laser Welding Procedure
After 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 (Pulsion Medical System AG, Munich, Germany) was prepared and applied to the walls of the surgical wound at the donor–recipient interface (see Figure 2 ).
A mild photothermal effect was induced by means of a near infrared diode laser (Mod. WELD 800; El.En., Calenzano, Florence, Italy) that emitted at 810 nm. The laser light was delivered through a 300-μm core diameter optical fiber that was mounted on a handpiece and used as if a pencil by the surgeon under a surgical microscope (see Figure 2 ). In a slow, continuous, and 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 ( Supplemental Video , available at AJO.com ). The power radiation emitted was a 60-mW continuous wave, which resulted in an 8-W/cm 2 power density on the tissue surface. The laser welding treatment time was set at 130s.
Postoperative Treatment and Examinations
At the end of the surgical procedure, a contact lens was placed on the cornea and removed after 1 week. After surgery, the patients were treated with tobramycin 0.3% and dexamethasone 0.1% ophthalmic suspension 4 times daily for 1 month, an application that then was tapered off slowly. They were also treated with an isotonic ophthalmic solution consisting of hyaluronic acid, sodium salt, and amino acids 4 to 6 times daily for approximately 6 months, a treatment that was then decreased. Patients were examined before surgery and then at 1 day, 7 days, 1 month, 3 months, 6 months, and 12 months after surgery. The following analyses were carried out by the same 2 examiners (A.C. and A.M.) each time: best spectacle-corrected distance visual acuity (CDVA), slit-lamp biomicroscopy, and dilated fundus examination. At all follow-up examinations, CDVA was recorded in both Snellen notation and in the logarithm of the minimal angle of resolution (logMAR) format as described by Holladay. For documentation of the visual acuity of patients who could not read all the letters on a single line correctly, the conversion was made by interpolating among the values of the logMAR acuity, using the fraction of the number of letters correctly read on a visual acuity line. Objective astigmatism and specular corneal topography (reported in diopters) were evaluated by using a topographer pachymeter (Sirius; CSO S.r.l, Scandicci, Florence, Italy). Endothelial cell density and central corneal pachymetry were measured with noncontact specular microscopy (Specular Microscope; New Tech s.p.a., Milano, Italy). All patients underwent anterior segment optical coherence tomography to evaluate wound alignment and suture configurations (Visante OCT; Carl Zeiss Meditec, Inc, Dublin, California, USA).
Results
No adverse events or complications occurred in any of the 24 PK cases during the laser-assisted surgery. The femtosecond laser was located in the operating room close to the microscope, where a trundle operating bed made all the procedures possible without moving the patient. In all cases, satisfactory intraoperative wound apposition was observed under the operating microscope, which facilitated the surgeon in placing the cardinal sutures. Minimal tension in the sutures was needed to secure the donor graft, thus reducing distortion on the part of the suture itself. Under the operating microscope, the morphologic features of the anvil profile appeared to be regular and consistent with the intended shape. The overall surgical procedure lasted an average of 45 minutes, including the preparation of the donor graft. As for the acuity evaluation, CDVA was observed to increase progressively at each follow-up examination and reached 0.13 ± 0.16 logMAR at 12 months after surgery ( Figure 3 ). Significant differences between preoperative and postoperative CDVA were observed at all times using the Student t test for paired sample to compare averages: P ≤ .05 was considered significant ( t = 5.49, t = 8.54, t = 9.80, and t = 10.96, respectively, at 1, 3, 6, and 12 months). When the 3 cases of preoperative retinal impairment, cataract, and slight amblyopia were excluded from the analysis, postoperative CDVA was found to be 0.47 ± 0.24 logMAR, 0.27 ± 0.17 logMAR, 0.16 ± 0.12 logMAR, and 0.09 ± 0.12 logMAR, respectively, at 1, 3, 6, and 12 months.
