title: Accuracy and precision of EyeSys and Orbscan systems on calibrated spherical test surfaces.
abstract: BACKGROUND
  It is important to know how well the surface topography can be measured with current devices for corneal topographic analysis. There are several applications that need an accurate and precise method to measure corneal shape and variations, such as the effect of contact lens wear and the different refractive surgery techniques.
  
  
  OBJECTIVE
  The aim of this study is to compare the accuracy and reproducibility of the measurement of the central curvature on calibrated steel balls using the EyeSys videokeratoscope and the Orbscan corneal topography system.
  
  
  METHODS
  The videokeratoscope (EyeSys Corneal Analysis System 2000, version 3.1) and the Orbscan corneal topography system (Orbscan II version 3.0) were used by four trained investigators to measure a series of five uniform and calibrated test surfaces with known radius of curvature ranging from 6.13 to 9.00 mm.
  
  
  RESULTS
  No statistically significant difference was found between the videokeratoscope and Orbscan systems in relation to accuracy or precision. The 95% confidence limits showed a close agreement between both instruments. The mean bias was less than +/-0.05 mm for both devices. The precision of the instruments was found to be similar.
  
  
  CONCLUSIONS
  The EyeSys seems to measure more accurately, but the accuracy of the Orbscan was also acceptable, suggesting that both instruments are accurate and precise enough for research and clinical purposes. However, further studies of accuracy and repeatability of topographical measurements on human eyes generated by different topographers are necessary.
authors.affiliation: School of Optometry, University of Santiago de Compostela, Galicia, Spain. fjavierg@usc.es
authors.forename: Javier
authors.initials: J
authors.lastname: González Pérez
authors.forename: A
authors.initials: A
authors.lastname: Cerviño
authors.forename: M J
authors.initials: MJ
authors.lastname: Giraldez
authors.forename: M
authors.initials: M
authors.lastname: Parafita
authors.forename: E
authors.initials: E
authors.lastname: Yebra-Pimentel
mesh_terms: D003315:Cornea / Q000033:anatomy & histology*; D019781:Corneal Topography / Q000295:instrumentation / Q000592:standards*; D006801:Humans; D008953:Models, Anatomic; D015203:Reproducibility of Results