title: Peripheral aberration measurements: elliptical pupil transformation and variations in horizontal coma across the visual field.
abstract: BACKGROUND
  The aim was to determine the critical eccentricity at which two methods of elaborating peripheral wavefront measurements are significantly different and to characterise horizontal coma in healthy young adults.
  
  
  METHODS
  Peripheral aberrations were determined for 20 observers for central and eight peripheral gaze positions up to 20° using an IRX-3 aberrometer. In one subject, additional measurements up to 40° were obtained. Two definitions of stretching coefficients were compared. The raw empirical data were compared with theoretical modelling.
  
  
  RESULTS
  For both 3.5 mm and 6.0 mm pupils, no significant differences were observed between recalculated and non-recalculated elliptical pupils for both methods (p > 0.05) up to 20° eccentricity. For eccentricities greater than 20° and up to 40°, significant differences between circular and elliptical pupils at some eccentricities were apparent, which corresponded to theoretical models. Wide individual variations in horizontal coma across the peripheral field were observed.
  
  
  CONCLUSIONS
  The data suggest that for eyes with average levels of aberrations, the elliptical transformation is of no practical importance for eccentricities up to 20°. In some cases the slope of horizontal coma was reversed compared with previous findings in normal eyes.
authors.affiliation: Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom.
authors.forename: Andreas
authors.initials: A
authors.lastname: Hartwig
authors.forename: Ian J
authors.initials: IJ
authors.lastname: Murray
authors.forename: Hema
authors.initials: H
authors.lastname: Radhakrishnan
mesh_terms: D000328:Adult; D001251:Astigmatism / Q000175:diagnosis / Q000503:physiopathology; D002138:Calibration; D019781:Corneal Topography / Q000379:methods / Q000592:standards*; D057108:Corneal Wavefront Aberration / Q000175:diagnosis* / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009216:Myopia / Q000175:diagnosis / Q000503:physiopathology; D011680:Pupil / Q000502:physiology*; D015203:Reproducibility of Results; D014794:Visual Fields / Q000502:physiology*; D055815:Young Adult