title: Repeatability and validity of Zywave aberrometer measurements.
abstract: OBJECTIVE
  To study the repeatability of Zywave aberrometer (Bausch & Lomb) measurements and compare the measurements with those of subjective refraction and noncycloplegic and cycloplegic autorefractions in a clinical setting.
  
  
  METHODS
  Department of Ophthalmology, University Hospital Maastricht, Maastricht, The Netherlands.
  
  
  METHODS
  Subjective manifest refraction, noncycloplegic autorefraction, cycloplegic autorefraction, and Zywave aberrometer measurements were performed in 20 eyes of 20 myopic patients. Three consecutive Zywave measurements were performed with and without dilation of the pupil. The mean difference and 95% limits of agreement among the measurement methods were determined for dilated and 3.5 mm pupils. The repeatability coefficient of the Zywave aberrometer measurements was determined.
  
  
  RESULTS
  The mean differences in spherical equivalent (SE), sphere, and cylinder between subjective refraction and Zywave predicted phoropter refraction (PPR) with a dilated pupil were -1.10 diopters (D) +/- 0.46 (SD) (P <.001), -1.08 +/- 0.44 D (P <.001), and -0.02 +/- 0.37 D (P =.87), respectively (paired Student t test). After the data were converted to a 3.5 mm pupil, the mean differences were -0.55 +/- 0.48 D (P <.001), -0.50 +/- 0.49 D (P <.001), and -0.16 +/- 0.50 D (P =.15), respectively. The mean difference in SE between autorefraction and cycloplegic autorefraction versus subjective refraction was +0.18 +/- 0.71 D (P =.27) and +0.35 +/- 0.62 D (P =.02), respectively. The mean difference in SE between cycloplegic autorefraction and Zywave PPR with a dilated pupil was -1.44 +/- 0.79 D (P <.001). The repeatability coefficient of Zywave PPR was +/-0.25 D for SE, +/-0.29 D for sphere, and +/-0.29 D for cylinder.
  
  
  CONCLUSIONS
  Subjective refraction measurements are slightly more myopic than cycloplegic autorefraction measurements. With a dilated pupil, the Zywave measurements were significantly more myopic than subjective refractions and even more myopic than cycloplegic autorefractions. Zywave measurements and subjective refractions were in better agreement with a 3.5 mm pupil. The repeatability of Zywave aberrometer measurements is adequate for lower-order aberrations.
authors.affiliation: Department of Ophthalmology, Academic Hospital Maastricht, P. Debyelaan 25, 6202 AZ Maastricht, The Netherlands.
authors.forename: Willem J
authors.initials: WJ
authors.lastname: Hament
authors.forename: Vaisjaly A
authors.initials: VA
authors.lastname: Nabar
authors.forename: Rudy M M A
authors.initials: RM
authors.lastname: Nuijts
mesh_terms: D000293:Adolescent; D000328:Adult; D003315:Cornea / Q000503:physiopathology*; D003941:Diagnostic Techniques, Ophthalmological; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology*; D012029:Refraction, Ocular / Q000502:physiology*; D015203:Reproducibility of Results