SMILE technique becomes a serious contender

The small incision lenticule extraction (SMILE) technique is becoming a serious contender for top corneal refractive surgery procedure as studies confirm both its efficacy and its theoretical advantages over LASIK, said José L Güell MD, Barcelona, Spain.

“What we have observed is that the refractive and visual results of SMILE are similar to the best ones achieved with excimer procedures and that it induces less inflammatory response and dryness. Furthermore, since the majority of biomechanical weakening with LASIK comes from the side-cut, it has obvious conceptual biomechanical advantages,” Dr Güell told the 19th ESCRS Winter Meeting in Istanbul, Turkey.

Over the years many corneal refractive techniques have come and gone despite showing great promise in theory, Dr Guell noted. The abandoned techniques include radial keratotomy, because of refractive instability, intracorneal ring segments and intracorneal lenses for ametropia, because of imprecision, although the latter two techniques have been adopted in more recent years for the treatment of ectasia and presbyopia, respectively.

It wasn’t until the introduction of excisional laser techniques like LASIK and photorefractive keratectomy (PRK) that refractive surgeons were able to provide patients with real precision and stability through corneal procedures. As a stromal treatment LASIK has additional advantages including the low tissue reaction. However it also has its shortcomings, Dr Güell said.

“The excimer laser is a fantastic tool, but has some limitations. We depend on environmental conditions in the operating room, we use gas, we need eye trackers and we have long ablation times, especially for the higher corrections. And of course with LASIK we are using an open flap and therefore have the risk of flap complications,” he added.

MEETING EXPECTATIONS

The SMILE femtosecond laser technique overcomes many of those disadvantages, since it uses a contact interface with good centration and is almost completely intrastromal and therefore does not involve an open flap. Moreover, it leaves the more strongly supportive and more heavily innervated anterior stromal layers almost completely intact, in theory providing better biomechanical stability and inducing less dry eye.

Data gathered over the last couple of years appear to have confirmed the safety and efficacy of the SMILE procedure as well as some of its proposed advantages, Dr Güell noted. The provisional data show that SMILE achieves refractive results equal to the best results achieved in matching eyes with LASIK, with 80 per cent to 90 per cent achieving an uncorrected visual acuity of 20/25 or better.

“We observe the slow but complete visual recovery which takes a few more days than it does with LASIK, possibly related to micro distortions that are produced by dissection of Bowman's membrane, which obviously is reversible after a few days or weeks after surgery,” Dr Güell said.

From an optical point of view, there are now also numerous studies showing that the scatter index after SMILE (OQAS-HD Analyzer data) is likewise close to that achieved in the best LASIK cases.

There is also evidence that the standard SMILE technique induces the same amount of secondary spherical aberration as does optimised LASIK with femtosecond laser-created flaps.

Regarding dry eye, in a study by Dan Reinstein MD, PhD and his associates in London (published in 2012), Cochet-Bonnet aesthesiometry showed considerably greater and longer-lasting reductions in corneal sensitivity after LASIK than after SMILE and this has been supported by other investigators.

In addition, the findings of rabbit eye studies indicate that there are fewer reflective particles and fibronectin and CD11b in the cornea after SMILE than after LASIK, showing that there is a lower inflammatory response after SMILE than there is to LASIK.

The surgical aspect of the SMILE technique consists of four basic steps, an anterior cut, a posterior cut, a small side cut, and extraction of the lenticule with a forceps, for some surgeons, and the cleaning of the interface.

“We still have some challenges such as re-operation, hyperopia correction and wavefront-guided corrections. But I think that the intrastromal laser approach is obviously the best and is a less aggressive approach to attack the cornea,” Dr Güell added.

José L Güell: guell@imo.es