title: Comparison of laser ray-tracing and skiascopic ocular wavefront-sensing devices.
abstract: OBJECTIVE
  To compare two wavefront-sensing devices based on different principles.
  
  
  METHODS
  Thirty-eight healthy eyes of 19 patients were measured five times in the reproducibility study. Twenty eyes of 10 patients were measured in the comparison study. The Tracey Visual Function Analyzer (VFA), based on the ray-tracing principle and the Nidek optical pathway difference (OPD)-Scan, based on the dynamic skiascopy principle were compared. Standard deviation (SD) of root mean square (RMS) errors was compared to verify the reproducibility. We evaluated RMS errors, Zernike terms and conventional refractive indexes (Sph, Cyl, Ax, and spherical equivalent).
  
  
  RESULTS
  In RMS errors reading, both devices showed similar ratios of SD to the mean measurement value (VFA: 57.5+/-11.7%, OPD-Scan: 53.9+/-10.9%). Comparison on the same eye showed that almost all terms were significantly greater using the VFA than using the OPD-Scan. However, certain high spatial frequency aberrations (tetrafoil, pentafoil, and hexafoil) were consistently measured near zero with the OPD-Scan.
  
  
  CONCLUSIONS
  Both devices showed similar level of reproducibility; however, there was considerable difference in the wavefront reading between machines when measuring the same eye. Differences in the number of sample points, centration, and measurement algorithms between the two instruments may explain our results.
authors.affiliation: Department of Ophthalmology, University of California San Diego, Shiley Eye Center, La Jolla, CA 92093-0946, USA. dbartsch@ucsd.edu
authors.forename: D-U G
authors.initials: DU
authors.lastname: Bartsch
authors.forename: K
authors.initials: K
authors.lastname: Bessho
authors.forename: L
authors.initials: L
authors.lastname: Gomez
authors.forename: W R
authors.initials: WR
authors.lastname: Freeman
mesh_terms: D000328:Adult; D000465:Algorithms; D019781:Corneal Topography; D004867:Equipment Design; D005260:Female; D006801:Humans; D007834:Lasers; D008297:Male; D012029:Refraction, Ocular / Q000502:physiology; D012030:Refractive Errors / Q000175:diagnosis* / Q000503:physiopathology; D015203:Reproducibility of Results; D042261:Retinoscopes; D042262:Retinoscopy / Q000379:methods*; D016896:Treatment Outcome