title: Accuracy of a dual Scheimpflug analyzer and a corneal topography system for intraocular lens power calculation in unoperated eyes.
abstract: OBJECTIVE
  To evaluate the accuracy of the corneal power measurements by a dual Scheimpflug analyzer (Galilei) and a corneal topography system (Keratron) for intraocular lens (IOL) power calculation in unoperated eyes.
  
  
  METHODS
  Private practice.
  
  
  METHODS
  Case series.
  
  
  METHODS
  The IOL power was calculated for eyes having phacoemulsification and in-the-bag IOL implantation by entering into the Hoffer Q, Holladay 1, and SRK/T formulas 3 corneal power measurements: (1) simulated keratometry (K) by corneal topography, (2) simulated K derived by anterior corneal curvature only using the dual Scheimpflug analyzer, (3) total corneal power derived by anterior and posterior corneal curvatures through ray tracing using the dual Scheimpflug analyzer. The prediction error was calculated as the difference between the predicted and the measured refraction 1 month postoperatively.
  
  
  RESULTS
  Forty-three consecutive patients were enrolled. The mean arithmetic error was zero for all combinations of measurements due to constant optimization. Using the Hoffer Q formula, the mean absolute prediction errors were 0.23 diopters (D) ± 0.22 (SD) for the corneal topographer simulated K, 0.21 ± 0.18 D for the Scheimpflug simulated K, and 0.27 ±0.20 D for the Scheimpflug total corneal power (P>.05). No statistically significant different results (compared with the Hoffer Q formula) were obtained with the Holladay 1 and SRK/T formulas.
  
  
  CONCLUSIONS
  Both devices provided corneal power measurements that led to accurate IOL power calculation. The total corneal power by the dual Scheimpflug system is the first corneal power measurement shown to lead to accurate IOL power calculation without using the standard keratometric index.
  
  
  BACKGROUND
  Drs. Savini, Barboni, and Carbonelli have no financial or proprietary interest in any material or method mentioned. Additional disclosures are found in the footnotes.
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; D019781:Corneal Topography; D005260:Female; D006801:Humans; D019654:Lens Implantation, Intraocular; D007910:Lenses, Intraocular; D008297:Male; D055095:Optics and Photonics; D018918:Phacoemulsification; D011446:Prospective Studies; D019591:Pseudophakia / Q000503:physiopathology*; D012029:Refraction, Ocular / Q000502:physiology*; D015203:Reproducibility of Results