title: Predicting ocular residual astigmatism using corneal and refractive parameters: a myopic eye study.
abstract: OBJECTIVE
  To investigate the nature of ocular residual astigmatism (ORA) in myopic patients and to identify indicators to predict a patient's ORA from corneal and ocular refractive data.
  
  
  METHODS
  In total, 356 myopic eyes from 178 patients (M:F = 41:137) were examined using a Scheimpflug keratometer (Pentacam) and a wavefront analyzer (WaveScan). Vertex distance-adjusted total ocular astigmatism and corneal astigmatism [anterior corneal power (ACP) and true net power (TNP)] were used to calculate ORA, respectively. A power vector system (J0 and J45) was adopted for the astigmatism analysis.
  
  
  RESULTS
  The mean age of the study eyes was 27.6 ± 5.0 years, and mean refractive spherical equivalent, sphere and cylinder was -4.94 ± 1.90 diopter, -4.42 ± 1.87 diopter, and -1.05 ± 0.82, respectively. Corneal astigmatism measured by TNP was more representative of total ocular astigmatism than ACP (p < 0.001). Both the J0 and J45 components of ORA showed significant negative correlation with corneal astigmatism measured by ACP and TNP (p < 0.001). ORA (J0 and J45) was negatively correlated with total ocular spherical equivalent and positively correlated with total ocular astigmatism.
  
  
  CONCLUSIONS
  We verified the general compensatory effect of corneal astigmatism by internal optics in myopic patients. TNP was closer to refractive astigmatism than ACP was. Total ocular spherical equivalent and total ocular astigmatism showed significant correlation with ORA. Therefore these can be possible indicators to predict ORA.
authors.affiliation: Department of Ophthalmology, Dongguk University, Ilsan Hospital, Koyang, Kyunggido, South Korea.
authors.forename: Choul Yong
authors.initials: CY
authors.lastname: Park
authors.forename: Jong-Hyun
authors.initials: JH
authors.lastname: Oh
authors.forename: Roy S
authors.initials: RS
authors.lastname: Chuck
mesh_terms: D000328:Adult; D001251:Astigmatism / Q000175:diagnosis* / Q000503:physiopathology; D003315:Cornea / Q000502:physiology; D019781:Corneal Topography / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009216:Myopia / Q000175:diagnosis* / Q000503:physiopathology; D010781:Photography / Q000379:methods; D011237:Predictive Value of Tests; D011680:Pupil / Q000502:physiology; D012029:Refraction, Ocular / Q000502:physiology*; D012189:Retrospective Studies; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult