A useful tool

The femtosecond laser can be a useful tool in several types of keratoplasty procedures, including penetrating and endothelial keratoplasty and keratoprosthesis surgery, said Luca Menabuoni MD, Nuovo Ospedale S Stefano, Prato, Italy, at Femto 2013 an international meeting on anterior segment surgery.

Dr Menabuoni noted that in eyes undergoing penetrating keratoplasty, the femtosecond laser enables the creation of closely matched interlocking trephination profiles in the donor and host corneas.

“The gold standard in penetrating keratoplasty is perfect flap adhesion, internal and external mechanical load resistance and the lowest endothelial cells pool to reduce the chance of rejection. The femtosecond laser can create trephination profiles with complex shapes and a large interface between the host and graft stroma,” Dr Menabuoni said.

Two commonly used profiles are the top-hat and mushroom profiles, he noted. However, because they have a weak load resistance, he has designed a new profile that he calls the anvil profile. Using an iFs 150 femtosecond laser (AMO) he creates matching profiles on the host and donor corneas the diameter of which is 7.5mm at the top, increasing to 8.5mm around the middle, below which is a trunk that is 6.5mm in diameter. This particular shape also preserves the patient’s endothelial cells pool.

When implanting the corneal button, he performs a procedure called corneal welding which is designed to enhance the adhesion of the graft to the host tissue. This technique is the result of a research collaboration with Drs Roberto Pini and Francesca Rossi from the Institute of Applied Physics (CNR) of Florence, Italy. It involves staining the trephined edges of both the host cornea and the donor button with a water solution of indocyanine green and then, after placing the graft in the eye, irradiating the graft-host junction with a near infrared (810 nm) diode laser operating at low power (12W/cm2).

Dr Menabuoni said that in 120 eyes in which he carried out penetrating keratoplasty with the anvil profile and corneal welding all surgeries were successful and without any intraoperative complications. “Short-term visual and refractive results with this technique have compared favourably with those achieved with conventional penetrating keratoplasty, although longer-term follow-up and comparative studies will be necessary to determine precisely the advantages of this technique,” he said.

OCT-guided endothelial keratoplasty

Dr Menabuoni noted that he has also developed an endothelial keratoplasty technique in which he uses the femtosecond laser combined with OCT to make grafts that are less than 90 microns in thickness.

When performing the technique he uses OCT to determine the thickness of the donor cornea. He then uses the femtosecond to trephine the cornea down to predetermined depth and then progressively reduces the thickness to 70 microns and then stains the edges of graft on the stromal side with indocyanine green for corneal welding.

He then performs manual stripping of the recipient eye and, using an EndoGlide™ (Angiotech), he draws the graft into position, injects an air bubble in the eye and closes the incisions used for the procedure with standard suturing. He concludes the procedure by welding the graft to the host cornea with a diode laser.

Dr Menabuoni said that, in the eyes he has performed the procedure, the one-year follow-up results have shown that the thin flap it enables the surgeon to create can provide a good recovery of visual functional and a modest endothelial cells loss. “The use of the intraoperative OCT, femtosecond laser for trephination and diode laser for suturing provides an improvement in endothelial keratoplasty and a rapid and better visual recovery once the graft is in place,” he added.

Dr Menabuoni has also developed a technique where he uses the femtosecond laser to prepare the carrier corneal button for the Boston type 1 keratoprosthesis (KPro). He noted that the technique provides better centration of the prosthesis on the visual axis and improves the regularity of the graft/host junction.

When preparing the donor cornea he uses just one applanation to perform the two concentric trephinations with a 150 kHz Intralase™ FS laser. He then makes the first 8.5mm diameter outer trephination followed by a concentric 3.0mm diameter inner trephination.

“The femtosecond laser-assisted double trephination results in a donor cornea correctly prepared, and in an inner side precisely matched with the prosthesis. At the end of the surgery the KPro is correctly centred, and the optimised match of carrier and donor cornea reduces the risk of endophthalmitis and melting due to the migration of coliquative germs and enzymes,” Dr Menabuoni said.

He added that the Boston K-pro has become widely accepted as the treatment of choice for patients with a history of repeated graft failure, Stevens-Johnson syndrome, ocular burns and other conditions likely to have a poor prognosis with penetrating keratoplasty.

“The femtosecond laser enables a new, safer and easier procedure to centre the KPro in the donor cornea,” he concluded.

Luca Menabuoni: luca.menabuoni@tin.it