title: Comparison of accuracy of intraocular lens calculations using automated keratometry, a Placido-based corneal topographer, and a combined Placido-based and dual Scheimpflug corneal topographer.
abstract: OBJECTIVE
  To compare the accuracy of intraocular lens (IOL) power calculations with automated keratometry, a Placido-based corneal topographer, and a combined Placido-based and dual Scheimpflug corneal topographer.
  
  
  METHODS
  Retrospectively, 75 eyes of 62 patients who had phacoemulsification with implantation of the SN60WF IOL were analyzed. Corneal powers were measured using 5 techniques: (1) automated keratometry (AutoK, IOL Master), (2) simulated keratometry from the Placido-based corneal topographer (SimKP, Atlas), (3) simulated keratometry from the combined Placido-based and dual Scheimpflug corneal topographer (SimKP+DS, Galilei), (4) total corneal power of the steep and flat meridians over a central 1.0-4.0 mm zone using ray tracing (TCPMeridian, Galilei), and (5) TCP over the central 4.0-mm zone by ray tracing (TCPCentral, Galilei). For each IOL implanted, prediction errors were determined by comparing the predicted refractions calculated with the Holladay 1 formula to the actual refraction that was obtained 3-4 weeks postoperatively. The surgeon factor was optimized for each method of corneal power measurement. The accuracy of IOL power calculation using these corneal powers was determined by calculating the mean absolute prediction error (MAE) and the percentage of eyes with prediction errors within 0.5, 1.0, and 1.5 diopters (D).
  
  
  RESULTS
  The MAEs were 0.37, 0.39, 0.39, 0.41, and 0.42 D for the AutoK, SimKP, SimKP+DS, TCPMeridian, and TCPCentral methods, respectively. There were no significant differences among groups. Over 93% of eyes had MAEs within 1.0 D for all methods of corneal power measurement.
  
  
  CONCLUSIONS
  The accuracy of IOL power calculation was comparable with AutoK, the Placido-based corneal topographer, and the combined Placido-based and dual Scheimpflug corneal topographer.
authors.affiliation: Department of Ophthalmology, Baylor College of Medicine, Houston, TX 77030, USA.
authors.forename: Mariko
authors.initials: M
authors.lastname: Shirayama
authors.forename: Li
authors.initials: L
authors.lastname: Wang
authors.forename: Douglas D
authors.initials: DD
authors.lastname: Koch
authors.forename: Mitchell P
authors.initials: MP
authors.lastname: Weikert
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D003315:Cornea / Q000502:physiology*; D019781:Corneal Topography / Q000295:instrumentation*; D005260:Female; D006801:Humans; D019654:Lens Implantation, Intraocular; D007910:Lenses, Intraocular; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D018918:Phacoemulsification; D012029:Refraction, Ocular / Q000502:physiology*; D012030:Refractive Errors / Q000175:diagnosis*; D015203:Reproducibility of Results; D012189:Retrospective Studies