title: Corneal Power Distribution and Functional Optical Zone Following Small Incision Lenticule Extraction for Myopia.
abstract: OBJECTIVE
  To evaluate corneal power distribution using the ray tracing method (corneal power) in eyes undergoing small incision lenticule extraction (SMILE) surgery and compare the functional optical zone with two lenticular sizes.
  
  
  METHODS
  This retrospective study evaluated 128 patients who underwent SMILE for the correction of myopia and astigmatism with a lenticular diameter of 6.5 mm (the 6.5-mm group) and 6.2 mm (the 6.2-mm group). The data include refraction, correction, and corneal power obtained via a Scheimpflug camera from the pupil center to 8 mm. The surgically induced changes in corneal power (Δcorneal power) were compared to correction and Δrefraction. The functional optical zone was defined as the largest ring diameter when the difference between the ring power and the pupil center power was 1.50 diopters or less. The functional optical zone was compared between two lenticular diameter groups.
  
  
  RESULTS
  Corneal power distribution was measured by the ray tracing method. In the 6.5-mm group (n=100), Δcorneal power at 5 mm showed the smallest difference from Δrefraction and Δcorneal power at 0 mm exhibited the smallest difference from correction. In the 6.2-mm group (n=28), Δcorneal power at 2 mm displayed the lowest dissimilarity from Δrefraction and Δcorneal power at 4 mm demonstrated the lowest dissimilarity from correction. There was no significant difference between the mean postoperative functional optical zones in either group when their spherical equivalents were matched.
  
  
  CONCLUSIONS
  Total corneal refactive power can be used in the evaluation of surgically induced changes following SMILE. A lenticular diameter of 6.2 mm should be recommended for patients with high myopia because there is no functional difference in the optical zone.
authors.forename: Yishan
authors.initials: Y
authors.lastname: Qian
authors.forename: Jia
authors.initials: J
authors.lastname: Huang
authors.forename: Xingtao
authors.initials: X
authors.lastname: Zhou
authors.forename: Rewais Benjamin
authors.initials: RB
authors.lastname: Hanna
mesh_terms: D000293:Adolescent; D000328:Adult; D001251:Astigmatism / Q000503:physiopathology / Q000601:surgery; D003315:Cornea / Q000502:physiology*; D003319:Corneal Stroma / Q000601:surgery; D005260:Female; D006801:Humans; D053685:Laser Therapy / Q000379:methods*; D008297:Male; D008866:Microsurgery / Q000379:methods; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D012029:Refraction, Ocular / Q000502:physiology; D012189:Retrospective Studies; D014792:Visual Acuity / Q000502:physiology*; D055815:Young Adult