title: Spherocylindrical refractive errors and visual acuity.
abstract: BACKGROUND
  Understanding the relation between refractive error and visual acuity is complicated if astigmatic blur is present. No models are in widespread use that allow the combination of spherical and astigmatic errors for the purpose of predicting visual performance.
  
  
  METHODS
  Models for combining spherical and astigmatic errors are discussed, and predictions of these models using data from the literature are presented.
  
  
  RESULTS
  Three models for combining astigmatic with spherical errors are shown to predict visual acuity performance in uncorrected myopic refractive errors. A dioptric vector addition model is shown to have advantages over other candidate models.
  
  
  CONCLUSIONS
  It is possible to combine spherocylindrical refractive errors into a single value when the objective is to correlate these values with visual acuity performance.
authors.affiliation: Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: T W
authors.initials: TW
authors.lastname: Raasch
mesh_terms: D005139:Eyeglasses; D006801:Humans; D008433:Mathematics; D008954:Models, Biological; D055095:Optics and Photonics; D012030:Refractive Errors / Q000503:physiopathology*; D014792:Visual Acuity / Q000502:physiology*