title: Topographic analysis of the centration of the treatment zone after SMILE for myopia and comparison to FS-LASIK: subjective versus objective alignment.
abstract: OBJECTIVE
  To evaluate the centration of the treatment zone after small incision lenticule extraction (SMILE) and compare it to femtosecond laser-assisted LASIK (FS-LASIK).
  
  
  METHODS
  Sixty-nine myopic eyes of 36 patients who underwent SMILE were compared to 69 myopic eyes of 36 patients treated with FS-LASIK. All procedures were performed by a single surgeon using the VisuMax platform (Carl Zeiss Meditec, Jena, Germany). The Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany) was used for preoperative and postoperative topography and pachymetry. The centration of the treatment zone was estimated pachymetrically by the distance of the thickest point on the corneal thickness differential map from the topographical center of the entrance pupil and the coaxial corneal light reflex.
  
  
  RESULTS
  In SMILE cases, the mean decentration of the lenticule from the center of the entrance pupil was 0.326 ± 0.196 mm (range: 0.014 to 1.062 mm), whereas the distribution of the lenticule centers demonstrated a nasalization pattern. In FS-LASIK cases, this value was 0.452 ± 0.224 mm (range: 0.02 to 1.040 mm), whereas the ablation centers were distributed randomly. In relation to the coaxial corneal light reflex, the decentration in SMILE was 0.315 ± 0.211 mm (range: 0.0 to 1.131 mm), whereas FS-LASIK eyes demonstrated a mean decentration of 0.516 ± 0.254 mm (range: 0.103 to 1.265 mm). The decentration from the reference point of its technique (coaxial corneal light reflex in SMILE, the entrance pupil center in FS-LASIK) was significantly more extended in the FS-LASIK group (P < .001).
  
  
  CONCLUSIONS
  The centration of the treatment zone as measured by the Pentacam was better for patient-controlled fixation during SMILE than active eye tracker-assisted FS-LASIK.
authors.forename: Apostolos
authors.initials: A
authors.lastname: Lazaridis
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Droutsas
authors.forename: Walter
authors.initials: W
authors.lastname: Sekundo
mesh_terms: D057128:Aberrometry; D000328:Adult; D000368:Aged; D003319:Corneal Stroma / Q000601:surgery*; D048988:Corneal Surgery, Laser / Q000379:methods*; D019781:Corneal Topography; D057108:Corneal Wavefront Aberration / Q000503:physiopathology; D005260:Female; D006801:Humans; D020731:Keratomileusis, Laser In Situ / Q000379:methods*; D054018:Lasers, Excimer / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D055815:Young Adult