Randomized, Non-inferiority Trial Comparing SMILE and LASIK

Surgical correction for refractive errors may be performed by a number of procedures. Laser correction involves procedures such as EpiLASIK, LASIK or conductive keratoplasty, while lens based corrections involve the use of phakic intra-ocular lenses. Despite the emergence of other procedures, due to its fast visual rehabilitation and painless postoperative course, LASIK is still the procedure of choice for both patients and refractive surgeons.

LASIK consists of two steps: the first step involves the formation of a corneal flap and the second one is when the excimer ablation is performed in the corneal stromal bed. Femtosecond lasers (FL) have been widely used in LASIK surgery to fashion the corneal flap. The laser will cut a lamellar followed by a vertical corneal incision. We are able to produce a vertical cut since the Femtosecond laser can deliver laser pulses of 1 micron diameter at a preselected depth in the cornea, which then expands to 2 to 3 microns with the formation of a cavitation bubble. These pulses create micro-photodisruption of the corneal tissue by the formation of an expanding bubble of carbon dioxide and water, which in turn cleaves the tissue and creates a plane of separation. The flap is then removed to expose the stroma and the refractive treatment is done by the excimer laser over the denuded stroma. The advantages of femtosecond laser over microkeratome LASIK flaps have been reduced postoperative dry eye symptoms, less chance of dislocation from trauma and reduced incidence of button holes or free caps.

Even though femto-LASIK has demonstrated good efficacy, it can still be asssociated with side effects found in standard LASIK e.g. glare, haloes, dry eye and still requires the use of two laser machines, one for the flap the other for the excimer ablation. This increases the length of time of the overall procedure and the costs.

Recently, a new "one laser" refractive surgery has been proposed: Femtosecond Lenticule Ex-traction (FLEx). It consists of performing the entire refractive procedure without an excimer laser. The Femtosecond laser creates four stromal incisions to create a corneal lenticule and a corneal flap. The size and shape of the lenticule is calculated based on the patient refractive error. The lenticule is separated from the flap above and the rest of the cornea below using a small spatula. Following this, the lenticule is grasped with a forceps and extracted from the eye. Finally, the flap is repositioned and the interface washed. At this time the refractive error is already corrected without the use of a second laser.

The advantages of FLEx treatment are shortened length of the refractive procedure, reduced patient inconvenience from moving from one laser to another, reduced risk of intraoperative infections and more accurate ablation since the patient need to fixate only once.

Currently there are no publications comparing FLEx to LASIK, hence this study will be unique in the fact that the paired eye approach will act as an internal patient control to assess the objective and subjective outcomes in patients following both these procedures.

The study will be a prospective randomized trial of patients comparing SMILE (a variation of FLEx) with LASIK to treat their myopic refractive error. One eye will be randomized for SMILE and other eye for LASIK. Each procedure will be performed sequentially. Randomization will be performed by a random number generator, and assignment concealed in envelopes.