title: Influence of axial length and corneal power on the  astigmatic power of toric intraocular lenses.
abstract: OBJECTIVE
  To assess the influence of the anterior chamber depth (ACD), predicted by corneal power (keratometry [K]), and axial length (AL) on the astigmatic power of toric intraocular lenses (IOLs).
  
  
  METHODS
  Private practice, Bologna, Italy.
  
  
  METHODS
  Noninterventional theoretical study.
  
  
  METHODS
  Meridional analysis (based on the Hoffer Q formula) was applied to an eye model with K ranging from 38.0 to 48.0 diopters and AL ranging from 20 to 30 mm. For each diopter (D) of K and each millimeter of AL, the ratio between the toricity at the IOL plane and the toricity at the corneal plane was computed. Several simulations with the Acrysof toric IOL were performed.
  
  
  RESULTS
  The ratio between toricity at the IOL plane and toricity at the corneal plane depended on the predicted ACD. The highest value (1.86) was found with the steepest K (48.0 D) and longest AL (30.0 mm) and the lowest value (1.29), with the flattest K (38.0 D) and shortest AL (20.0 mm). When applied to the toric IOL, the results suggest that a low ratio (≤1.41) led to overcorrection of astigmatism relative to the value reported by the manufacturer's online calculator. In contrast, a high ratio (>1.60) led to undercorrection of the astigmatism.
  
  
  CONCLUSIONS
  The ACD influenced the ratio between the cylinder power in the IOL plane and the cylinder power in the corneal plane and should be accounted for when selecting a toric IOL in an eye whose K and AL are far from the average values.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Savini
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Hoffer
authors.forename: Michele
authors.initials: M
authors.lastname: Carbonelli
authors.forename: Pietro
authors.initials: P
authors.lastname: Ducoli
authors.forename: Piero
authors.initials: P
authors.lastname: Barboni
mesh_terms: D001251:Astigmatism / Q000503:physiopathology* / Q000601:surgery; D058452:Axial Length, Eye / Q000502:physiology*; D003315:Cornea / Q000502:physiology*; D019781:Corneal Topography; D006801:Humans; D019654:Lens Implantation, Intraocular; D007910:Lenses, Intraocular; D008962:Models, Theoretical; D055095:Optics and Photonics; D018918:Phacoemulsification; D012029:Refraction, Ocular / Q000502:physiology*