A Review of Corneal Biomechanics after LASIK and SMILE and the Current Methods of Corneal Biomechanical Analysis

Corneal refractive surgeries for the correction of myopia, hyperopia, astigmatism and hyperopia are quick and effective procedures, and have been growing in popularity over the last two decades. However, post-surgery corneal ectasia remains one of the most feared surgical complications. This is where the biomechanical integrity of the cornea begins to fail, with progressive thinning of the stroma, steepening of the cornea, irregular astigmatism, and decreased distance visual acuity. Laser-assisted in-situ keratomileusis (LASIK) is currently the most common refractive surgery procedure. It uses a femtosecond laser or a microkeratome to cut a thin flap on the surface of the cornea. Corneal tissue is then photoablated to correct the refractive error and the flap is then replaced at the end of the procedure. Newer techniques such as small incision lenticule extraction (SMILE) make use of a small incision only, without flap creation, and a lenticule is extracted to correct the refractive error. The avoidance of flap creation should theoretically maintain the integrity of the anterior corneal region and lower the risk of corneal ectasia, but there have been few clinical studies to date that compare the corneal biomechanical outcomes of different procedures. In this review, we highlight the biomechanical differences in outcomes between LASIK and SMILE, as well as explain some of the in vivo and in vitro techniques to investigate corneal biomechanical parameters.