Corneal biomechanical stability is better, less affected by flapless refractive procedure
The study included 60 eyes of 30 patients divided into two groups. The same femtosecond laser (VisuMax 500, Carl Zeiss Meditec) was used to create the LASIK flaps and the lenticule for the SMILE procedure, and the LASIK ablations were performed using a single excimer laser platform (WaveLight Allegretto, Alcon, Fort Worth, Texas, USA).
All LASIK flaps and SMILE caps had an attempted thickness of 90 μm. Corneal biomechanics were assessed using the Ocular Response Analyzer (ORA, Reichert, Munich, Germany) to measure corneal hysteresis (CH) and corneal resistance factor (CRF) at three months preoperatively and three months postoperatively.
Mean percent change in CH was –6.7% in the SMILE group and –17.4% in the femto-LASIK group. Mean percent change in CRF was –9.7% for the SMILE group and –22% for the femto-LASIK group. The reduction in CH did not correlate with the amount or percentage of corneal tissue removed nor with the optical zone or patient age.
"SMILE is a one-step, non-ablative corneal refractive procedure in which a lenticule of tissue is cut by the femtosecond laser and removed through a small incision," explained Dr Abdalla, cornea and refractive surgery senior fellow, Cornea Centre, Alexandria, Egypt. "This technique avoids recognized flap complications, including postoperative discomfort and dry eye, and as a flapless procedure, we consider SMILE the laser vision correction procedure of choice for patients involved in contact sports.
"In addition, based on our study, SMILE appears to offer better biomechanical stability than the flap-based procedure," continued Dr Abdalla. "However, further studies are warranted to confirm our findings, including in a larger patient population and ideally using better methods to evaluate corneal biomechanics."