title: Accuracy of corneal power measurements by a new Scheimpflug camera combined with Placido-disk corneal topography for intraocular lens power calculation in unoperated eyes.
abstract: OBJECTIVE
  To assess the accuracy of the corneal power measurements with a new Scheimpflug camera combined with Placido-disk corneal topography (Sirius) (combined Scheimpflug camera-topographer) for intraocular lens (IOL) power calculation in unoperated eyes and compare the results with those by a validated corneal topographer (Keratron) (validated topographer).
  
  
  METHODS
  Private practice.
  
  
  METHODS
  Case series.
  
  
  METHODS
  Consecutive patients having phacoemulsification and in-the-bag IOL implantation were studied. Intraocular lens power was calculated using the Hoffer Q, Holladay 1, and SRK/T formulas; the axial length, as measured by ultrasound immersion biometry; and 3 corneal power measurements: validated topographer simulated keratometry (K); combined Scheimpflug camera-topographer simulated K (derived from anterior corneal curvature only); combined Scheimpflug camera-topographer mean pupil power (derived from anterior and posterior corneal curvatures through ray tracing). The prediction error was calculated as the difference between the predicted refraction and the refraction measured 1 month postoperatively.
  
  
  RESULTS
  When the corneal power measurements from the combined Scheimpflug camera-topographer were used, the mean absolute error (MAE) ranged between 0.23 diopter (D) ± 0.24 (SD) (simulated K and Hoffer Q formula) and 0.33 ± 0.23 D (mean pupil power and SRK/T formula). There were no statistically significant differences between the MAE generated by the simulated Ks of the 2 devices with any of the 3 formulas.
  
  
  CONCLUSIONS
  Both corneal power measurements (simulated K and mean pupil power) provided by the new combined Scheimpflug camera-topographer were successfully entered into third-generation IOL power calculation formulas in unoperated eyes.
  
  
  BACKGROUND
  Dr. Hoffer is the author of the Hoffer Q formula and owns the EyeLab, which sells Hoffer Programs. No other author has a financial or proprietary interest in any material or method mentioned.
authors.affiliation: G.B. Bietti Eye Foundation-IRCCS, Rome, Italy. giacomo.savini@alice.it
authors.forename: Giacomo
authors.initials: G
authors.lastname: Savini
authors.forename: Piero
authors.initials: P
authors.lastname: Barboni
authors.forename: Michele
authors.initials: M
authors.lastname: Carbonelli
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Hoffer
mesh_terms: D000368:Aged; D058452:Axial Length, Eye; D001699:Biometry / Q000379:methods; D003315:Cornea / Q000502:physiology*; D019781:Corneal Topography / Q000379:methods*; D005260:Female; D006801:Humans; D019654:Lens Implantation, Intraocular; D007910:Lenses, Intraocular; D008297:Male; D055095:Optics and Photonics; D018918:Phacoemulsification; D010781:Photography / Q000379:methods*; D011446:Prospective Studies; D012029:Refraction, Ocular / Q000502:physiology; D015203:Reproducibility of Results