title: [Nomograms for the improvement of refractive outcomes].
abstract: BACKGROUND
  Nomograms are efficient tools to improve the predictability of refractive procedures by using statistical methods to analyze pre- and postoperative refractive data. The purpose of this work was to analyze the clinical relevance and limitations of nomograms in a case series.
  
  
  METHODS
  Computer simulations based on the known unpredictability for refractive outcomes were performed for three different distribution functions of the preoperative refractions. In addition, the clinical applicability was investigated in three different cohorts that underwent laser in situ keratomileusis (LASIK).
  
  
  RESULTS
  The use of individual nomograms significantly improves the predictability of the refractive outcome. However, theoretical investigation demonstrates that a homogeneous data distribution within cohorts is a key factor for predictable nomogram calculations. Outliers within the cohorts are not integrated into the nomogram calculation due to the mathematical model used.
  
  
  CONCLUSIONS
  Nomograms are helpful for improving refractive outcomes. However, they are currently limited to approximately 90% within +/-0.5 D.
authors.affiliation: IROC AG, Institut für Refraktive und Ophthalmo-Chirurgie, Zürich, Schweiz.
authors.forename: M
authors.initials: M
authors.lastname: Mrochen
authors.forename: F
authors.initials: F
authors.lastname: Hafezi
authors.forename: H P
authors.initials: HP
authors.lastname: Iseli
authors.forename: J
authors.initials: J
authors.lastname: Löffler
authors.forename: T
authors.initials: T
authors.lastname: Seiler
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D003198:Computer Simulation; D004867:Equipment Design; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D020731:Keratomileusis, Laser In Situ / Q000592:standards*; D008297:Male; D008432:Mathematical Computing; D008875:Middle Aged; D049451:Nomograms; D017063:Outcome Assessment, Health Care / Q000706:statistics & numerical data; D011183:Postoperative Complications / Q000175:diagnosis*; D012029:Refraction, Ocular; D012030:Refractive Errors / Q000175:diagnosis; D054140:Refractive Surgical Procedures