title: A ray tracing approach to calculate toric intraocular lenses.
abstract: OBJECTIVE
  To quantify the precision of astigmatic correction in routine cataract surgery with toric intraocular lenses (IOLs) and to evaluate the predictability of keratometric and anterior/posterior topographic measurement for the improvement of the overall accuracy.
  
  
  METHODS
  Seventy-eight eyes of 56 patients were implanted with toric IOLs. Data acquired by the Lenstar optical biometer (Haag-Streit, Bern, Switzerland) and TMS5 topography (Tomey, Nagoya, Japan) were processed with the ray tracing software Okulix (Tedics, Dortmund, Germany) to predict the residual refraction. Four different inputs were examined: keratometry only, anterior topography, anterior and posterior topography/ tomography, and combination of keratometry only and anterior and posterior topography/tomography. Four weeks postoperatively, the spherical prediction error and the cylindrical prediction error (difference vector between predicted and achieved cylindrical refraction) were determined.
  
  
  RESULTS
  Mean absolute error of spherical prediction error was 0.27 diopter (D). Cylindrical prediction errors were 0.57 D (keratometry only), 0.56 D (anterior topography), 0.56 D (anterior and posterior topography/ tomography), and 0.50 D (combination of keratometry only and anterior and posterior topography/tomography). Differences between intraocular lens groups were statistically significant (Friedman test, P < .05).
  
  
  CONCLUSIONS
  The combination of keratometry and anterior and posterior topography/tomography of anterior and posterior surface yielded the best results for toric IOL power calculations.
authors.affiliation: Augen-und-Laserklinik, Castrop-Rauxel, Germany. ph@augenklinik-castrop-rauxel.de
authors.forename: Peter C
authors.initials: PC
authors.lastname: Hoffmann
authors.forename: Jochen
authors.initials: J
authors.lastname: Wahl
authors.forename: Werner W
authors.initials: WW
authors.lastname: Hütz
authors.forename: Paul-Rolf
authors.initials: PR
authors.lastname: Preußner
mesh_terms: D001699:Biometry / Q000379:methods*; D006801:Humans; D007910:Lenses, Intraocular / Q000592:standards*; D055620:Optical Phenomena; D011474:Prosthesis Design; D012984:Software