Femto Lasers

Femtosecond lasers are finding a diverse range of uses in keratoplasty procedures, although the expense of the instruments must be weighed against the relatively modest benefits, if any, that they provide in terms of visual outcomes, according to several presenters speaking at Femto 2013, an international meeting on anterior segment surgery. “Femtosecond lasers provide customised corneal patterns, cut very precisely and with a perfect correspondence between the donor and recipient cornea, maximising the surface area of the wound and providing greater wound stability and increased resistance to wound leakage,” said Romina Fasciani MD.

She noted that because of the precision of the femtosecond trephination it could theoretically make the penetrating keratoplasty procedure into a more repeatable technique that could result in faster visual rehabilitation, less postoperative astigmatism and greater wound strength with less risk of wound dehiscence during suture removal. In the Eye Clinic of Catholic University of “Sacro Cuore” in Rome with Prof Emilio Balestrazzi and Dr Luigi Mosca, we have experienced the effectiveness of lamellar and penetrating keratoplasty assisted by femtosecond laser. Research conducted to date indicate that with current technology femtosecond laserassisted penetrating keratoplasty results in better wound adhesion and more rapid improvement in acuity and permits earlier suture removal than is the case with standard penetrating keratoplasty, Dr Fasciani said.

However, the lasers provide little if any advantage over penetrating keratoplasty in terms of postoperative astigmatism in the long term and the rates of endothelial cell loss with the lasers has ranged very widely, from under five per cent to over 30 per cent. Moreover, the newer technology is also more expensive, takes longer, and generally entails the use of general anaesthesia. There are a number of trephination profiles that are possible with the femtosecond laser, such as the mushroom, the top hat, the zigzag and the Christmas tree. There are also several new trephination profiles that are coming into clinical use, including the dovetail, the bolt and decagonal shapes. Future trends to watch out for include the use of anterior segment OCT to precisely guide the trephination, and the use of fibrin glue or laser corneal welding to seal and secure the shaped opposing wound edges, Dr Fasciani added.

Femto DALK

In eyes where the pathology affects only the anterior cornea, deep anterior lamellar keratoplasty (DALK) is a useful option since it spares the recipient’s endothelium and greatly reduces the risk of corneal rejection. The use of femtosecond laser in such cases has the same potential benefits as it does with penetrating keratoplasty, said Elisabetta Bohm MD, Ospedale dell'Angelo, Venice-Mestre, Italy. “Femtosecond DALK provides simplicity and also safety because of the larger scar, which should grant a stronger graft. Its learning curve is also short,” she said. Cases particularly suited to femtosecond laser-assisted DALK include young patients, because the tighter wound apposition they afford would offer better protection against ocular trauma. DALK may be useful in eyes with vascularised corneas, because the perfect smoothness of the laser cut, very seldom followed by any inflammation, may inhibit vascular re-growth.

Cases unsuited to the procedure include those where a suction ring cannot be applied, such as in eyes with conjunctival oedema. Also unsuited are eyes with thin and damaged corneas, as in the case of corneal hydrops, where the pressure exerted by the cone could be harmful. She noted that she and her associates use mainly the mushroom and diamond profiles when performing femtosecond-laserassisted DALK procedure, and each have their advantages. The mushroom profile has the greatest effect on the anterior cornea and requires only a small bubble to cleave the residual stroma from the Descemet’s membrane. The diamond profile makes it easier for the surgeon to perform the final cutting of the stroma from the periphery of the denuded Descemet’s membrane.

Femto DSEK

Endothelial keratoplasty has the opposite advantage from DALK in that it leaves the anterior cornea intact and replaces only the host endothelium with as little of donor stroma attached to it as possible. Preparation of the donor posterior lamellar disc with a femtosecond laser enables the creation of planar grafts with micrometer precision, independent of the limitations of microkeratome mechanics, said Mor M Dickman MD, University Eye clinic Maastricht, the Netherlands, Maastricht. However, the results of the Dutch Lamellar Corneal Transplantation Study (DLCTS), indicate that femtosecond laserassisted Descemet’s-stripping endothelial keratoplasty produces results inferior to those of penetrating keratoplasty in terms of visual acuity and endothelial cell survival, he said.

As part of the prospective randomised multicentre study, Dr Nuijts and his associates compared the results achieved in 36 eyes that underwent a laser assisted procedure with 40 eyes that underwent penetrating keratoplasty. At one year’s follow-up, mean BCVA was 20/70 lines in the femtosecond laser-assisted DSEK group and 20/44 in the penetrating keratoplasty group (P < .001) despite significant improvement in both refractive and topographic astigmatism in the DSEK group. The main factor limiting visual acuity was interface wound healing. In addition, endothelial cell counts fell to around 1,000 cells/mm2 in the DSEK group compared to 2,000 cells/mm2 in the penetrating keratoplasty group. "This finding is likely related to the learning curve of different surgeons, as preliminary in vitro studies have shown that femtosecond laser assisted endothelial graft dissection is not associated with significant endothelial cell loss," Dr Dickman said.