title: Estimating the Preoperative Corneal Power With Scheimpflug Imaging in Eyes That Have Undergone Myopic LASIK.
abstract: OBJECTIVE
  To investigate whether the Estimated Pre-Refractive SimK accurately predicts the preoperative corneal power (K) in eyes with previous myopic femtosecond laser-assisted LASIK (FS-LASIK) and whether a better prediction can be developed.
  
  
  METHODS
  Preoperatively and 3 months after FS-LASIK, patients underwent anterior segment imaging with the Pentacam HR rotating Scheimpflug camera (Oculus Optikgeräte, Wetzlar, Germany). Posterior and anterior corneal curvature and power and asphericity (Q-value at 8 mm) were recorded. Multiple linear regression was used to assess the relationship among variables.
  
  
  RESULTS
  One hundred four eyes of 104 patients were enrolled. The Estimated Pre-Refractive SimK (43.19 ± 1.63 diopters [D]) was lower (P = .0014) than the mean preoperative K (43.44 ± 1.49 D). The difference was within ±0.50 and ±1.00 D in 53.8% and 86.5% of eyes, respectively. Multiple linear regression detected a statistically significant relationship (r(2) = 0.8497, P < .0001) among the investigated parameters: preoperative anterior corneal radius = 1.156 + 1.012 * postoperative posterior corneal radius - 0.3800 * postoperative Q-value. When this equation was used to predict the preoperative K, the difference between the actual preoperative K and the predicted value (43.41 ± 1.38 D) was not statistically significant. The rate of eyes with a difference between the predicted and actual preoperative K within ±0.50 and ±1.00 D increased to 61.5% and 93.3%, respectively.
  
  
  CONCLUSIONS
  The corneal power before FS-LASIK can be accurately predicted from the postoperative corneal measurements of a rotating Scheimpflug camera. The multiple regression formula described may be more accurate than the Estimated Pre-Refractive SimK available on the Pentacam. [J Refract Surg. 2016;32(5):332-336.].
authors.forename: Giacomo
authors.initials: G
authors.lastname: Savini
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Hoffer
authors.forename: Domenico
authors.initials: D
authors.lastname: Schiano-Lomoriello
authors.forename: Pietro
authors.initials: P
authors.lastname: Ducoli
mesh_terms: D000328:Adult; D000368:Aged; D003315:Cornea / Q000503:physiopathology*; D003952:Diagnostic Imaging / Q000379:methods; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D006801:Humans; D020731:Keratomileusis, Laser In Situ / Q000379:methods*; D054018:Lasers, Excimer / Q000627:therapeutic use*; D019654:Lens Implantation, Intraocular; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D055095:Optics and Photonics; D057234:Preoperative Period; D011446:Prospective Studies; D012029:Refraction, Ocular / Q000502:physiology*; D055815:Young Adult