Small incision lenticule extraction (SMILE) versus laser in-situ keratomileusis (LASIK): study protocol for a randomized, non-inferiority trial (Trials)

Background: Small incision lenticule extraction or SMILE is a novel form of `flapless` corneal refractivesurgery that was adapted from refractive lenticule extraction (ReLEx). SMILE uses only onefemtosecond laser to complete the refractive surgery, potentially reducing surgical time, sideeffects, and cost. If successful, SMILE could potentially replace the current, widely practicedlaser in-situ keratomileusis or LASIK. The aim of this study is to evaluate whether SMILE isnon-inferior to LASIK in terms of refractive outcomes at 3 months post-operatively. Methods: Single tertiary center, parallel group, single-masked, paired-eye design, non-inferiority,randomized controlled trial. Participants who are eligible for LASIK will be enrolled forstudy after informed consent. Each participant will be randomized to receive SMILE andLASIK in each eye. Our primary hypothesis (stated as null) in this non-inferiority trial wouldbe that SMILE differs from LASIK in adults (>21 years old) with myopia (> 3.00 diopter(D)) at a tertiary eye center in terms of refractive predictability at 3 months post-operatively.Our secondary hypothesis (stated as null) in this non-inferiority trial would be that SMILEdiffers from LASIK in adults (>21 years old) with myopia (> 3.00 D) at a tertiary eye centerin terms of other refractive outcomes (efficacy, safety, higher-order aberrations) at 3 monthspost-operatively. Our primary outcome is refractive predictability, which is one of severalstandard refractive outcomes, defined as the proportion of eyes achieving a postoperativespherical equivalent (SE) within +/-0.50 D of the intended target. Randomization will beperformed using random allocation sequence generated by a computer with no blocks orrestrictions, and implemented by concealing the number-coded surgery within sealedenvelopes until just before the procedure. In this single-masked trial, subjects and theircaregivers will be masked to the assigned treatment in each eye.DiscussionThis novel trial will provide information on whether SMILE has comparable, if not superior,refractive outcomes compared to the established LASIK for myopia, thus providing evidencefor translation into clinical practice.Trial registrationClinicaltrials.gov NCT01216475.