title: An analysis of the factors influencing the residual refractive astigmatism after cataract surgery with toric intraocular lenses.
abstract: OBJECTIVE
  To investigate the influence of posterior corneal astigmatism, surgically-induced corneal astigmatism (SICA), intraocular lens (IOL) orientation, and effective lens position on the refractive outcome of toric IOLs.
  
  
  METHODS
  Five models were prospectively investigated. Keratometric astigmatism and an intended SICA of 0.2 diopters (D) were entered into model 1. Total corneal astigmatism, measured by a rotating Scheimpflug camera, was used instead of keratometric astigmatism in model 2. The mean postoperative SICA, the actual postoperative IOL orientation, and the influence of the effective lens position were added, respectively, into models 3, 4, and 5. Astigmatic data were vectorially described by meridional and torsional powers. A set of equations was developed to describe the error in refractive astigmatism (ERA) as the difference between the postoperative refractive astigmatism and the target refractive astigmatism.
  
  
  RESULTS
  We enrolled 40 consecutive eyes. In model 1, ERA calculations revealed significant cylinder overcorrection in with-the-rule (WTR) eyes (meridional power = -0.59 ± 0.34 D, P < 0.0001) and undercorrection in against-the-rule (ATR) eyes (0.32 ± 0.42 D, P = 0.01). When total corneal astigmatism was used instead of keratometric astigmatism (model 2), the ERA meridional power decreased in WTR (-0.13 ± 0.42 D) and ATR (0.07 ± 0.59 D) eyes, both values being not statistically significant. Models 3 to 5 did not lead to significant improvement.
  
  
  CONCLUSIONS
  Posterior corneal astigmatism exerts the highest influence on the ERA after toric IOL implantation. Basing calculations on total corneal astigmatism rather than keratometric astigmatism improves the prediction of the residual refractive astigmatism.
authors.affiliation: Fondazione GB Bietti IRCCS, Rome, Italy.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Savini
authors.affiliation: Regions Hospital Randers, Randers, Denmark.
authors.forename: Kristian
authors.initials: K
authors.lastname: Næser
mesh_terms: D000368:Aged; D001251:Astigmatism / Q000503:physiopathology* / Q000601:surgery; D003315:Cornea / Q000473:pathology / Q000601:surgery*; D019781:Corneal Topography; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007910:Lenses, Intraocular; D008297:Male; D018918:Phacoemulsification / Q000009:adverse effects*; D011379:Prognosis; D011446:Prospective Studies; D011474:Prosthesis Design; D012029:Refraction, Ocular / Q000502:physiology*; D014792:Visual Acuity
keywords: astigmatism; mathematics; polar values; toric IOL