title: Ocular residual astigmatism and topographic disparity vector indexes in normal healthy eyes.
abstract: OBJECTIVE
  To define a range of normality for the vectorial parameters Ocular Residual Astigmatism (ORA) and topography disparity (TD) and to evaluate their relationship with visual, refractive, anterior and posterior corneal curvature, pachymetric and corneal volume data in normal healthy eyes.
  
  
  METHODS
  This study comprised a total of 101 consecutive normal healthy eyes of 101 patients ranging in age from 15 to 64 years old. In all cases, a complete corneal analysis was performed using a Scheimpflug photography-based topography system (Pentacam system Oculus Optikgeräte GmbH). Anterior corneal topographic data were imported from the Pentacam system to the iASSORT software (ASSORT Pty. Ltd.), which allowed the calculation of the ocular residual astigmatism (ORA) and topography disparity (TD). Linear regression analysis was used for obtaining a linear expression relating ORA and posterior corneal astigmatism (PCA).
  
  
  RESULTS
  Mean magnitude of ORA was 0.79 D (SD: 0.43), with a normality range from 0 to 1.63D. 90 eyes (89.1%) showed against-the-rule ORA. A weak although statistically significant correlation was found between the magnitudes of posterior corneal astigmatism and ORA (r=0.34, p<0.01). Regression analysis showed the presence of a linear relationship between these two variables, although with a very limited predictability (R(2): 0.08). Mean magnitude of TD was 0.89D (SD: 0.50), with a normality range from 0 to 1.87D.
  
  
  CONCLUSIONS
  The magnitude of the vector parameters ORA and TD is lower than 1.9D in the healthy human eye.
authors.affiliation: Ocular Surface and Cornea Unit, Department of Ophthalmology, Oftalmar, Hospital Internacional Medimar, Alicante, Spain; Foundation for the Visual Quality (FUNCAVIS, Fundación para la Calidad Visual), Alicante, Spain; Department of Optics, Pharmacology and Anatomy, University of Alicante, Spain. Electronic address: david.pinyero@ua.es.
authors.forename: David P
authors.initials: DP
authors.lastname: Piñero
authors.affiliation: Ocular Surface and Cornea Unit, Department of Ophthalmology, Oftalmar, Hospital Internacional Medimar, Alicante, Spain.
authors.forename: Pedro
authors.initials: P
authors.lastname: Ruiz-Fortes
authors.affiliation: Ocular Surface and Cornea Unit, Department of Ophthalmology, Oftalmar, Hospital Internacional Medimar, Alicante, Spain; Foundation for the Visual Quality (FUNCAVIS, Fundación para la Calidad Visual), Alicante, Spain.
authors.forename: Rafael J
authors.initials: RJ
authors.lastname: Pérez-Cambrodí
authors.affiliation: Department of Optics, Pharmacology and Anatomy, University of Alicante, Spain.
authors.forename: Verónica
authors.initials: V
authors.lastname: Mateo
authors.affiliation: Ocular Surface and Cornea Unit, Department of Ophthalmology, Oftalmar, Hospital Internacional Medimar, Alicante, Spain.
authors.forename: Alberto
authors.initials: A
authors.lastname: Artola
mesh_terms: D000293:Adolescent; D000328:Adult; D001251:Astigmatism / Q000175:diagnosis* / Q000503:physiopathology; D003315:Cornea / Q000033:anatomy & histology; D019781:Corneal Topography; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012029:Refraction, Ocular / Q000502:physiology*; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult
keywords: Corneal astigmatism; Ocular residual astigmatism; Posterior corneal astigmatism; Topography disparity