VERSATILITY OF FEMTOSECOND LASER

The femtosecond laser is fast becoming the Swiss-army knife of the corneal surgeon, opening up new possibilities in an ever-broadening range of indications, said Sonia H Yoo MD, Bascom Palmer Institute, University of Miami Miller School of Medicine, Miami, Florida. “Femtosecond laser technology is a corneal surgeon’s dream and it is an evolving technology with limitless potential,†Dr Yoo said at the XXIX Congress of the ESCRS.

The femtosecond laser was originally marketed roughly a decade ago as a replacement for the microkeratome in LASIK surgery. Corneal surgeons soon began to investigate the femtosecond laser’s use in other forms of corneal surgery. She noted that, since first acquiring a femtosecond laser in 2004, she and her associates have been exploring its potential in the treatment of special refractive cases.

One example of an additional use for the laser is to facilitate the re-lifting of LASIK flaps in eyes undergoing retreatments several years after the initial procedure, Dr Yoo noted. To that end, she and her associates use a technique that involves the creation of side-cuts within the side-cuts of the original LASIK flaps. The precision of the femtosecond laser enables the surgeon incise the cornea just to the depth of the original cut.

Another application of the femtosecond laser in corneal surgery is the creation of channels for placement of intrastromal ring segment. The femtosecond laser provides a precise control of the depth of channel placement and the size optical zone. That, in turn, permits a more accurate titration of the stromal ring segments’ refractive effect.  

Dr Yoo noted that she has also achieved very good results with the femtosecond laser in the performance of astigmatic keratotomy in the treatment of post-keratoplasty astigmatism. In one such case she was able to reduce cylinder from -11.0 D to 0.5 D.

She and her associates have also been working to further refine the technique by adopting a sub-Bowman’s approach, to reduce under- and over-corrections and reduce epithelial ingrowth and the dry eye that results from cutting across corneal nerves. She described the case of a patient who had 1.75 D of astigmatism after undergoing implantation of a multifocal IOL. Following a sub-Bowman’s arcuate incision with a femtosecond laser, the patient had a manifest cylinder of 0.5 D and an improved uncorrected visual acuity. Moreover, postoperative OCT imaging showed clearly that the incisions were below Bowman’s membrane, she said.

Keratoplasty

The femtosecond laser is also useful in both penetrating and non-penetrating keratoplasty procedures. For example, in penetrating keratoplasty, the femtosecond laser makes it easy to create side-cuts of the button and host cornea that can be optimised for the treatment of anterior cornea, as in the case of corneal scarring, or for the posterior cornea as in the case of endothelial disease. In the former case, a mushroom cut would preserve as much endothelium as possible, and in the latter case a top hat pattern would preserve as much of the anterior corneal surface as possible.

“I hope that in my career I will no longer be suturing penetrating keratoplasty grafts. My hope and my dream is that we will be able to combine this technology that maximises surface area and optimises fit between the donor and the recipient and couple it with bioadhesives so that we can simply glue or adhere this lenticule into place without the need for sutures,†Dr Yoo commented.

She noted that femtosecond laser-assisted anterior lamellar grafts are possible in eyes with corneal scars where the scar is limited to the anterior half of the cornea and there is adequate posterior thickness.

The microkeratome remains the best tool in deep anterior lamellar keratoplasty for the preparation of both the donor tissue and the patient’s cornea. That is because DALK performed with a microkeratome results in a smoother stroma-to stroma interface. However, it may be that future improved versions of the femtosecond laser or some other laser technology may be able to create interlamellar cuts as smooth as or smoother than those of a microkeratome, she noted.

Microkeratomes also produce better results than femtosecond lasers in the preparation of graft tissue for DSAEK procedures. However, the lasers are very useful in the creation of a Descemetorhexis in the recipient’s eye, greatly facilitating the surgery, Dr Yoo said.

“The femtosecond laser has changed how corneal and cataract surgery are performed and will continue to do so in the future.â€