title: Visual acuity measurements using Fourier series harmonic analysis of videokeratography data in eyes after penetrating keratoplasty.
abstract: OBJECTIVE
  Fourier harmonic analysis can decompose videokeratography data into spherical power, regular astigmatism, and irregular astigmatism (asymmetry and higher-order irregularity). The aim of this study was to evaluate whether determination of cylinder power by Fourier analysis facilitates measurements of visual acuity and refraction in eyes after penetrating keratoplasty.
  
  
  METHODS
  Cross-sectional study.
  
  
  METHODS
  Sixty-six eyes of 56 subjects who had undergone penetrating keratoplasty.
  
  
  METHODS
  Spectacle-corrected visual acuity was measured in 2 ways: by the conventional and the Fourier methods. In the conventional method, the refraction was determined subjectively by reference to the measurement results of the autokeratometer and autorefractometer. In the Fourier method, the magnitude and axis of regular astigmatism were calculated by Fourier analysis of the videokeratography data, and spherical lenses were adjusted until best spectacle-corrected visual acuity was attained.
  
  
  METHODS
  Logarithm of the minimum angle of resolution (logMAR) visual acuity and refraction used for correction.
  
  
  RESULTS
  The spectacle-corrected visual acuity obtained with the Fourier method (logMAR, 0.23+/-0.32; Snellen equivalent, 20/34) was significantly better than that attained with the conventional method (logMAR, 0.31+/-0.29; Snellen equivalent, 20/41; P<0.001, paired t test). The cylinder power used for spectacle-corrected visual acuity measurements was significantly lower with the Fourier method (-2.41+/-1.26 diopters [D]) than with the conventional method (-3.53+/-1.64 D; P<0.001). The spherical equivalent at the final refraction was not different between groups (P = 0.207).
  
  
  CONCLUSIONS
  Fourier analysis of videokeratography data significantly facilitates determination of refraction and measurement of best spectacle-corrected visual acuity in eyes with corneal irregular astigmatism, such as eyes that have undergone penetrating keratoplasty.
authors.affiliation: Meiwakai Medical Foundation, Miyata Eye Hospital, Miyazaki, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Miyai
authors.forename: Kazunori
authors.initials: K
authors.lastname: Miyata
authors.forename: Ryohei
authors.initials: R
authors.lastname: Nejima
authors.forename: Tomokazu
authors.initials: T
authors.lastname: Samejima
authors.forename: Takahiro
authors.initials: T
authors.lastname: Hiraoka
authors.forename: Takahiro
authors.initials: T
authors.lastname: Kiuchi
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Kaji
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Oshika
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001251:Astigmatism / Q000175:diagnosis* / Q000209:etiology; D003315:Cornea / Q000473:pathology*; D019781:Corneal Topography / Q000379:methods*; D003430:Cross-Sectional Studies; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D015948:Keratoplasty, Penetrating; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications; D012029:Refraction, Ocular; D014792:Visual Acuity