title: Comparison of methods to measure corneal power for intraocular lens power calculation using a rotating Scheimpflug camera.
abstract: OBJECTIVE
  To assess the accuracy of corneal power measurements provided by a Scheimpflug camera (Pentacam HR) for intraocular lens (IOL) power calculation in unoperated eyes and compare the results with those of simulated keratometry (SimK) performed with a Placido-disk corneal topographer (Keratron).
  
  
  METHODS
  Private practice.
  
  
  METHODS
  Evaluation of diagnostic test.
  
  
  METHODS
  Eight Scheimpflug camera corneal power measurements were analyzed: (1) average K, (2) true net power calculated using the Gaussian optics formula, (3) total corneal refractive power at 2.0 mm calculated by ray tracing on a ring and (4) as the average of the zone inside the ring, (5) total corneal refractive power at 3.0 mm on a ring and (6) as the average of the zone inside the ring, (7) the equivalent K reading at 3.0 mm and (8) at 4.5 mm. The IOL power was calculated using the Hoffer Q, Holladay 1, and SRK/T formulas.
  
  
  RESULTS
  No statistically significant differences were observed between any corneal power measurements, including simulated K, in 41 consecutive patients. The latter showed slightly lower mean absolute errors with all 3 formulas (range 0.26 to 0.27 diopter [D]). The Scheimpflug camera gave the lowest median absolute errors with all formulas; that is, the 3.0 mm equivalent K reading with the Hoffer Q formula (0.18 D) and Holladay 1 formula (0.17 D) and the 2.0 mm total corneal refractive power ring with the SRK/T formula (0.18 D).
  
  
  CONCLUSIONS
  Corneal power measurements provided by the Scheimpflug camera and Placido disk corneal topographer displayed comparable accuracy in IOL power calculation.
authors: G.B. Bietti Foundation IRCCS, Rome, Italy. giacomo.savini@alice.it
authors: Giacomo
authors: G
authors: Savini
authors: Piero
authors: P
authors: Barboni
authors: Michele
authors: M
authors: Carbonelli
authors: Kenneth J
authors: KJ
authors: Hoffer
mesh_terms: D000368:Aged; D003315:Cornea / Q000502:physiology*; D019781:Corneal Topography; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D006801:Humans; D007910:Lenses, Intraocular; D008297:Male; D055095:Optics and Photonics; D010781:Photography / Q000295:instrumentation*; D011446:Prospective Studies; D012029:Refraction, Ocular / Q000502:physiology*; D015203:Reproducibility of Results