title: Influence factors of estimation errors for total corneal astigmatism using keratometric astigmatism in patients before cataract surgery.
abstract: OBJECTIVE
  To evaluate the influence factors of the estimation errors for total corneal astigmatism using keratometric astigmatism in patients preparing for cataract surgery.
  
  
  METHODS
  EYE and ENT Hospital of Fudan University, Shanghai, China.
  
  
  METHODS
  Prospective observational study.
  
  
  METHODS
  Eyes of patients preparing for cataract surgery were measured with Pentacam Scheimpflug imaging device. Keratometric astigmatism was obtained using the anterior corneal surface measurement and the keratometric index (1.3375) while neglecting the posterior corneal surface measurement. The Scheimpflug-measured total corneal astigmatism was derived by vector analysis of the astigmatism on both corneal surfaces.
  
  
  RESULTS
  The study comprised 374 eyes of 374 patients 45 to 84 years old. The mean absolute error in magnitude and mean absolute error in angle comparing keratometric astigmatism with Scheimpflug-derived astigmatism was 0.18 ± 0.14 diopter (D) and 7.7 ± 11.0 degrees, respectively. The mean magnitude of the error vector was 0.24 ± 0.14 D. The error in magnitude was significantly larger in eyes with against-the-rule anterior astigmatism, while error in angle was larger in eyes with with-the-rule and oblique anterior astigmatism. Multiple regressions showed that 4 predictors (difference in anterior-posterior astigmatism axis, magnitude of posterior astigmatism, magnitude of keratometric astigmatism, and axial length [AL]) were significantly associated with the absolute error in magnitude. Predictors including the difference in the anterior-posterior astigmatism axis, magnitude of posterior astigmatism, magnitude of keratometric astigmatism, and age were significantly associated with the absolute error in angle and magnitude of the error vector.
  
  
  CONCLUSIONS
  Neglecting posterior corneal astigmatism yielded significant estimation errors in total corneal astigmatism in patients preparing for cataract surgery. Estimation errors were significantly influenced by the difference in the anterior -posterior astigmatism axis, magnitude of posterior astigmatism, keratometric astigmatism, AL, and age.
  
  
  BACKGROUND
  None of the authors has any conflicts of interest to disclose.
authors.affiliation: From the Department of Ophthalmology (Zheng, Lu), EYE and ENT Hospital of Fudan University, Shanghai, China; Southern California Environmental Health Sciences Center (Chen), Department of Preventive Medicine, University of Southern California, Los Angeles, California, USA.
authors.forename: Tianyu
authors.initials: T
authors.lastname: Zheng
authors.affiliation: From the Department of Ophthalmology (Zheng, Lu), EYE and ENT Hospital of Fudan University, Shanghai, China; Southern California Environmental Health Sciences Center (Chen), Department of Preventive Medicine, University of Southern California, Los Angeles, California, USA.
authors.forename: Zhanghua
authors.initials: Z
authors.lastname: Chen
authors.affiliation: From the Department of Ophthalmology (Zheng, Lu), EYE and ENT Hospital of Fudan University, Shanghai, China; Southern California Environmental Health Sciences Center (Chen), Department of Preventive Medicine, University of Southern California, Los Angeles, California, USA. Electronic address: luyi0705@126.com.
authors.forename: Yi
authors.initials: Y
authors.lastname: Lu
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology; D001251:Astigmatism / Q000175:diagnosis*; D058452:Axial Length, Eye / Q000473:pathology; D001699:Biometry / Q000295:instrumentation*; D002387:Cataract Extraction; D003315:Cornea / Q000473:pathology*; D003951:Diagnostic Errors; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012307:Risk Factors