title: Stability of corneal topography and wavefront aberrations in young Singaporeans.
abstract: BACKGROUND
  The aim was to investigate the differences between and variations across time in corneal topography and ocular wavefront aberrations in young Singaporean myopes and emmetropes.
  
  
  METHODS
  We used a videokeratoscope and wavefront sensor to measure the ocular surface topography and wavefront aberrations of the total-eye optics in the morning, midday and late afternoon on two separate days. Topographic data were used to derive the corneal surface wavefront aberrations. Both the corneal and total wavefronts were analysed up to the fourth radial order of the Zernike polynomial expansion and were centred on the entrance pupil (5.0 mm). The participants included 12 young progressing myopes, 13 young stable myopes and 15 young age-matched emmetropes.
  
  
  RESULTS
  For all subjects considered together, there were significant changes in some of the aberrations across the day, such as spherical aberration ( Z(4 0)) and vertical coma ( Z (3 - 1)) (repeated measures analysis of variance, p < 0.05). The magnitude of positive spherical aberration ( Z(4 0)) was significantly lower in the progressing myopic group than in the stable myopic (p = 0.04) and emmetropic (p = 0.02) groups. There were also significant interactions between refractive group and time of day for with and against-the-rule astigmatism ( Z(2 2)). Significantly lower fourth-order root mean square of ocular wavefront aberrations were found in the progressing myopic group compared with the stable myopes and emmetropes (p < 0.01).
  
  
  CONCLUSIONS
  These differences and variations in the corneal and total aberrations may have significance for our understanding of refractive error development and for clinical applications requiring accurate wavefront measurements.
authors.affiliation: Optometry Centre, School of Chemical and Life Sciences, Singapore Polytechnic, Singapore. zhumingxia@sp.edu.sg
authors.forename: Mingxia
authors.initials: M
authors.lastname: Zhu
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Collins
authors.forename: Anna C H
authors.initials: AC
authors.lastname: Yeo
mesh_terms: D000293:Adolescent; D001251:Astigmatism / Q000175:diagnosis* / Q000503:physiopathology; D019781:Corneal Topography / Q000379:methods*; D057108:Corneal Wavefront Aberration / Q000175:diagnosis* / Q000503:physiopathology; D018450:Disease Progression; D058453:Emmetropia; D005260:Female; D006801:Humans; D008029:Lighting; D008297:Male; D009216:Myopia / Q000175:diagnosis* / Q000503:physiopathology; D012030:Refractive Errors / Q000175:diagnosis* / Q000503:physiopathology; D012846:Singapore; D013997:Time Factors; D055815:Young Adult
keywords: cornea; ocular surface topography; ocular wavefront aberrations; spherical aberration